Merge remote branch 'rails/master' into identity_map

Conflicts:
	activerecord/lib/active_record/associations/association_proxy.rb
	activerecord/lib/active_record/autosave_association.rb
	activerecord/lib/active_record/base.rb
	activerecord/lib/active_record/persistence.rb

51 files changed, 1213 insertions, 1067 deletions

diff --git a/activerecord/lib/active_record/association_preload.rb b/activerecord/lib/active_record/association_preload.rb
index 54a964f53b..373532704f 100644
--- a/activerecord/lib/active_record/association_preload.rb
+++ b/activerecord/lib/active_record/association_preload.rb
@@ -253,6 +253,7 @@ module ActiveRecord
               through_record_id = through_record[reflection.through_reflection_primary_key].to_s
               add_preloaded_records_to_collection(id_to_record_map[through_record_id], reflection.name, through_record.send(source))
             end
+            records.each { |record| record.send(reflection.name).target.uniq! } if options[:uniq]
           end
 
         else
@@ -393,9 +394,9 @@ module ActiveRecord
       # Some databases impose a limit on the number of ids in a list (in Oracle its 1000)
       # Make several smaller queries if necessary or make one query if the adapter supports it
       def associated_records(ids)
-        max_ids_in_a_list = connection.ids_in_list_limit || ids.size
+        in_clause_length = connection.in_clause_length || ids.size
         records = []
-        ids.each_slice(max_ids_in_a_list) do |some_ids|
+        ids.each_slice(in_clause_length) do |some_ids|
           records += yield(some_ids)
         end
         records
diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index fd9f000147..371dad9104 100644
--- a/activerecord/lib/active_record/associations.rb
+++ b/activerecord/lib/active_record/associations.rb
@@ -4,6 +4,8 @@ require 'active_support/core_ext/module/delegation'
 require 'active_support/core_ext/object/blank'
 require 'active_support/core_ext/string/conversions'
 require 'active_support/core_ext/module/remove_method'
+require 'active_support/core_ext/class/attribute'
+require 'active_record/associations/class_methods/join_dependency'
 
 module ActiveRecord
   class InverseOfAssociationNotFoundError < ActiveRecordError #:nodoc:
@@ -1227,12 +1229,14 @@ module ActiveRecord
 
         if reflection.options[:polymorphic]
           association_accessor_methods(reflection, BelongsToPolymorphicAssociation)
+          association_foreign_type_setter_method(reflection)
         else
           association_accessor_methods(reflection, BelongsToAssociation)
           association_constructor_method(:build,  reflection, BelongsToAssociation)
           association_constructor_method(:create, reflection, BelongsToAssociation)
         end
 
+        association_foreign_key_setter_method(reflection)
         add_counter_cache_callbacks(reflection)          if options[:counter_cache]
         add_touch_callbacks(reflection, options[:touch]) if options[:touch]
 
@@ -1559,6 +1563,45 @@ module ActiveRecord
           end
         end
 
+        def association_foreign_key_setter_method(reflection)
+          setters = reflect_on_all_associations(:belongs_to).map do |belongs_to_reflection|
+            if belongs_to_reflection.primary_key_name == reflection.primary_key_name
+              "association_instance_set(:#{belongs_to_reflection.name}, nil);"
+            end
+          end.compact.join
+
+          if method_defined?(:"#{reflection.primary_key_name}=")
+            undef_method :"#{reflection.primary_key_name}="
+          end
+
+          class_eval <<-FILE, __FILE__, __LINE__ + 1
+            def #{reflection.primary_key_name}=(new_id)
+              write_attribute :#{reflection.primary_key_name}, new_id
+              if #{reflection.primary_key_name}_changed?
+                #{ setters }
+              end
+            end
+          FILE
+        end
+
+        def association_foreign_type_setter_method(reflection)
+          setters = reflect_on_all_associations(:belongs_to).map do |belongs_to_reflection|
+            if belongs_to_reflection.options[:foreign_type] == reflection.options[:foreign_type]
+              "association_instance_set(:#{belongs_to_reflection.name}, nil);"
+            end
+          end.compact.join
+
+          field = reflection.options[:foreign_type]
+          class_eval <<-FILE, __FILE__, __LINE__ + 1
+            def #{field}=(new_id)
+              write_attribute :#{field}, new_id
+              if #{field}_changed?
+                #{ setters }
+              end
+            end
+          FILE
+        end
+
         def add_counter_cache_callbacks(reflection)
           cache_column = reflection.counter_cache_column
 
@@ -1816,12 +1859,12 @@ module ActiveRecord
           callbacks.each do |callback_name|
             full_callback_name = "#{callback_name}_for_#{association_name}"
             defined_callbacks = options[callback_name.to_sym]
-            if options.has_key?(callback_name.to_sym)
-              class_inheritable_reader full_callback_name.to_sym
-              write_inheritable_attribute(full_callback_name.to_sym, [defined_callbacks].flatten)
-            else
-              write_inheritable_attribute(full_callback_name.to_sym, [])
-            end
+
+            full_callback_value = options.has_key?(callback_name.to_sym) ? [defined_callbacks].flatten : []
+
+            # TODO : why do i need method_defined? I think its because of the inheritance chain
+            class_attribute full_callback_name.to_sym unless method_defined?(full_callback_name)
+            self.send("#{full_callback_name}=", full_callback_value)
           end
         end
 
@@ -1837,580 +1880,6 @@ module ActiveRecord
             Array.wrap(extensions)
           end
         end
-
-        class JoinDependency # :nodoc:
-          attr_reader :join_parts, :reflections, :table_aliases
-
-          def initialize(base, associations, joins)
-            @join_parts            = [JoinBase.new(base, joins)]
-            @associations          = {}
-            @reflections           = []
-            @table_aliases         = Hash.new(0)
-            @table_aliases[base.table_name] = 1
-            build(associations)
-          end
-
-          def graft(*associations)
-            associations.each do |association|
-              join_associations.detect {|a| association == a} ||
-              build(association.reflection.name, association.find_parent_in(self) || join_base, association.join_type)
-            end
-            self
-          end
-
-          def join_associations
-            join_parts.last(join_parts.length - 1)
-          end
-
-          def join_base
-            join_parts.first
-          end
-
-          def count_aliases_from_table_joins(name)
-            # quoted_name should be downcased as some database adapters (Oracle) return quoted name in uppercase
-            quoted_name = join_base.active_record.connection.quote_table_name(name.downcase).downcase
-            join_sql = join_base.table_joins.to_s.downcase
-            join_sql.blank? ? 0 :
-              # Table names
-              join_sql.scan(/join(?:\s+\w+)?\s+#{quoted_name}\son/).size +
-              # Table aliases
-              join_sql.scan(/join(?:\s+\w+)?\s+\S+\s+#{quoted_name}\son/).size
-          end
-
-          def instantiate(rows)
-            primary_key = join_base.aliased_primary_key
-            parents = {}
-
-            records = rows.map { |model|
-              primary_id = model[primary_key]
-              parent = parents[primary_id] ||= join_base.instantiate(model)
-              construct(parent, @associations, join_associations.dup, model)
-              parent
-            }.uniq
-
-            remove_duplicate_results!(join_base.active_record, records, @associations)
-            records
-          end
-
-          def remove_duplicate_results!(base, records, associations)
-            case associations
-              when Symbol, String
-                reflection = base.reflections[associations]
-                remove_uniq_by_reflection(reflection, records)
-              when Array
-                associations.each do |association|
-                  remove_duplicate_results!(base, records, association)
-                end
-              when Hash
-                associations.keys.each do |name|
-                  reflection = base.reflections[name]
-                  remove_uniq_by_reflection(reflection, records)
-
-                  parent_records = []
-                  records.each do |record|
-                    if descendant = record.send(reflection.name)
-                      if reflection.collection?
-                        parent_records.concat descendant.target.uniq
-                      else
-                        parent_records << descendant
-                      end
-                    end
-                  end
-
-                  remove_duplicate_results!(reflection.klass, parent_records, associations[name]) unless parent_records.empty?
-                end
-            end
-          end
-
-          protected
-
-            def cache_joined_association(association)
-              associations = []
-              parent = association.parent
-              while parent != join_base
-                associations.unshift(parent.reflection.name)
-                parent = parent.parent
-              end
-              ref = @associations
-              associations.each do |key|
-                ref = ref[key]
-              end
-              ref[association.reflection.name] ||= {}
-            end
-
-            def build(associations, parent = nil, join_type = Arel::InnerJoin)
-              parent ||= join_parts.last
-              case associations
-                when Symbol, String
-                  reflection = parent.reflections[associations.to_s.intern] or
-                  raise ConfigurationError, "Association named '#{ associations }' was not found; perhaps you misspelled it?"
-                  unless join_association = find_join_association(reflection, parent)
-                    @reflections << reflection
-                    join_association = build_join_association(reflection, parent)
-                    join_association.join_type = join_type
-                    @join_parts << join_association
-                    cache_joined_association(join_association)
-                  end
-                  join_association
-                when Array
-                  associations.each do |association|
-                    build(association, parent, join_type)
-                  end
-                when Hash
-                  associations.keys.sort{|a,b|a.to_s<=>b.to_s}.each do |name|
-                    join_association = build(name, parent, join_type)
-                    build(associations[name], join_association, join_type)
-                  end
-                else
-                  raise ConfigurationError, associations.inspect
-              end
-            end
-
-            def find_join_association(name_or_reflection, parent)
-              if String === name_or_reflection
-                name_or_reflection = name_or_reflection.to_sym
-              end
-
-              join_associations.detect { |j|
-                j.reflection == name_or_reflection && j.parent == parent
-              }
-            end
-
-            def remove_uniq_by_reflection(reflection, records)
-              if reflection && reflection.collection?
-                records.each { |record| record.send(reflection.name).target.uniq! }
-              end
-            end
-
-            def build_join_association(reflection, parent)
-              JoinAssociation.new(reflection, self, parent)
-            end
-
-            def construct(parent, associations, join_parts, row)
-              case associations
-              when Symbol, String
-                name = associations.to_s
-
-                join_part = join_parts.detect { |j|
-                  j.reflection.name.to_s == name &&
-                  j.parent_table_name    == parent.class.table_name }
-
-                raise(ConfigurationError, "No such association") unless join_part
-
-                join_parts.delete(join_part)
-                construct_association(parent, join_part, row)
-              when Array
-                associations.each do |association|
-                  construct(parent, association, join_parts, row)
-                end
-              when Hash
-                associations.sort_by { |k,_| k.to_s }.each do |name, assoc|
-                  association = construct(parent, name, join_parts, row)
-                  construct(association, assoc, join_parts, row) if association
-                end
-              else
-                raise ConfigurationError, associations.inspect
-              end
-            end
-
-            def construct_association(record, join_part, row)
-              return if record.id.to_s != join_part.parent.record_id(row).to_s
-
-              macro = join_part.reflection.macro
-              if macro == :has_one
-                return if record.instance_variable_defined?("@#{join_part.reflection.name}")
-                association = join_part.instantiate(row) unless row[join_part.aliased_primary_key].nil?
-                set_target_and_inverse(join_part, association, record)
-              else
-                return if row[join_part.aliased_primary_key].nil?
-                association = join_part.instantiate(row)
-                case macro
-                when :has_many, :has_and_belongs_to_many
-                  collection = record.send(join_part.reflection.name)
-                  collection.loaded
-                  collection.target.push(association)
-                  collection.__send__(:set_inverse_instance, association, record)
-                when :belongs_to
-                  set_target_and_inverse(join_part, association, record)
-                else
-                  raise ConfigurationError, "unknown macro: #{join_part.reflection.macro}"
-                end
-              end
-              association
-            end
-
-            def set_target_and_inverse(join_part, association, record)
-              association_proxy = record.send("set_#{join_part.reflection.name}_target", association)
-              association_proxy.__send__(:set_inverse_instance, association, record)
-            end
-
-          # A JoinPart represents a part of a JoinDependency. It is an abstract class, inherited
-          # by JoinBase and JoinAssociation. A JoinBase represents the Active Record which
-          # everything else is being joined onto. A JoinAssociation represents an association which
-          # is joining to the base. A JoinAssociation may result in more than one actual join
-          # operations (for example a has_and_belongs_to_many JoinAssociation would result in
-          # two; one for the join table and one for the target table).
-          class JoinPart # :nodoc:
-            # The Active Record class which this join part is associated 'about'; for a JoinBase
-            # this is the actual base model, for a JoinAssociation this is the target model of the
-            # association.
-            attr_reader :active_record
-
-            delegate :table_name, :column_names, :primary_key, :reflections, :sanitize_sql, :arel_engine, :to => :active_record
-
-            def initialize(active_record)
-              @active_record = active_record
-              @cached_record = {}
-            end
-
-            def ==(other)
-              raise NotImplementedError
-            end
-
-            # An Arel::Table for the active_record
-            def table
-              raise NotImplementedError
-            end
-
-            # The prefix to be used when aliasing columns in the active_record's table
-            def aliased_prefix
-              raise NotImplementedError
-            end
-
-            # The alias for the active_record's table
-            def aliased_table_name
-              raise NotImplementedError
-            end
-
-            # The alias for the primary key of the active_record's table
-            def aliased_primary_key
-              "#{aliased_prefix}_r0"
-            end
-
-            # An array of [column_name, alias] pairs for the table
-            def column_names_with_alias
-              unless defined?(@column_names_with_alias)
-                @column_names_with_alias = []
-
-                ([primary_key] + (column_names - [primary_key])).each_with_index do |column_name, i|
-                  @column_names_with_alias << [column_name, "#{aliased_prefix}_r#{i}"]
-                end
-              end
-
-              @column_names_with_alias
-            end
-
-            def extract_record(row)
-              Hash[column_names_with_alias.map{|cn, an| [cn, row[an]]}]
-            end
-
-            def record_id(row)
-              row[aliased_primary_key]
-            end
-
-            def instantiate(row)
-              @cached_record[record_id(row)] ||= active_record.send(:instantiate, extract_record(row))
-            end
-          end
-
-          class JoinBase < JoinPart # :nodoc:
-            # Extra joins provided when the JoinDependency was created
-            attr_reader :table_joins
-
-            def initialize(active_record, joins = nil)
-              super(active_record)
-              @table_joins = joins
-            end
-
-            def ==(other)
-              other.class == self.class &&
-              other.active_record == active_record
-            end
-
-            def aliased_prefix
-              "t0"
-            end
-
-            def table
-              Arel::Table.new(table_name, :engine => arel_engine, :columns => active_record.columns)
-            end
-
-            def aliased_table_name
-              active_record.table_name
-            end
-          end
-
-          class JoinAssociation < JoinPart # :nodoc:
-            # The reflection of the association represented
-            attr_reader :reflection
-
-            # The JoinDependency object which this JoinAssociation exists within. This is mainly
-            # relevant for generating aliases which do not conflict with other joins which are
-            # part of the query.
-            attr_reader :join_dependency
-
-            # A JoinBase instance representing the active record we are joining onto.
-            # (So in Author.has_many :posts, the Author would be that base record.)
-            attr_reader :parent
-
-            # What type of join will be generated, either Arel::InnerJoin (default) or Arel::OuterJoin
-            attr_accessor :join_type
-
-            # These implement abstract methods from the superclass
-            attr_reader :aliased_prefix, :aliased_table_name
-
-            delegate :options, :through_reflection, :source_reflection, :to => :reflection
-            delegate :table, :table_name, :to => :parent, :prefix => true
-
-            def initialize(reflection, join_dependency, parent = nil)
-              reflection.check_validity!
-
-              if reflection.options[:polymorphic]
-                raise EagerLoadPolymorphicError.new(reflection)
-              end
-
-              super(reflection.klass)
-
-              @reflection      = reflection
-              @join_dependency = join_dependency
-              @parent          = parent
-              @join_type       = Arel::InnerJoin
-
-              # This must be done eagerly upon initialisation because the alias which is produced
-              # depends on the state of the join dependency, but we want it to work the same way
-              # every time.
-              allocate_aliases
-            end
-
-            def ==(other)
-              other.class == self.class &&
-              other.reflection == reflection &&
-              other.parent == parent
-            end
-
-            def find_parent_in(other_join_dependency)
-              other_join_dependency.join_parts.detect do |join_part|
-                self.parent == join_part
-              end
-            end
-
-            def join_to(relation)
-              send("join_#{reflection.macro}_to", relation)
-            end
-
-            def join_relation(joining_relation)
-              self.join_type = Arel::OuterJoin
-              joining_relation.joins(self)
-            end
-
-            def table
-              @table ||= Arel::Table.new(
-                table_name, :as => aliased_table_name,
-                :engine => arel_engine, :columns => active_record.columns
-              )
-            end
-
-            # More semantic name given we are talking about associations
-            alias_method :target_table, :table
-
-            protected
-
-              def aliased_table_name_for(name, suffix = nil)
-                if @join_dependency.table_aliases[name].zero?
-                  @join_dependency.table_aliases[name] = @join_dependency.count_aliases_from_table_joins(name)
-                end
-
-                if !@join_dependency.table_aliases[name].zero? # We need an alias
-                  name = active_record.connection.table_alias_for "#{pluralize(reflection.name)}_#{parent_table_name}#{suffix}"
-                  @join_dependency.table_aliases[name] += 1
-                  if @join_dependency.table_aliases[name] == 1 # First time we've seen this name
-                    # Also need to count the aliases from the table_aliases to avoid incorrect count
-                    @join_dependency.table_aliases[name] += @join_dependency.count_aliases_from_table_joins(name)
-                  end
-                  table_index = @join_dependency.table_aliases[name]
-                  name = name[0..active_record.connection.table_alias_length-3] + "_#{table_index}" if table_index > 1
-                else
-                  @join_dependency.table_aliases[name] += 1
-                end
-
-                name
-              end
-
-              def pluralize(table_name)
-                ActiveRecord::Base.pluralize_table_names ? table_name.to_s.pluralize : table_name
-              end
-
-              def interpolate_sql(sql)
-                instance_eval("%@#{sql.gsub('@', '\@')}@", __FILE__, __LINE__)
-              end
-
-            private
-
-            def allocate_aliases
-              @aliased_prefix     = "t#{ join_dependency.join_parts.size }"
-              @aliased_table_name = aliased_table_name_for(table_name)
-
-              if reflection.macro == :has_and_belongs_to_many
-                @aliased_join_table_name = aliased_table_name_for(reflection.options[:join_table], "_join")
-              elsif [:has_many, :has_one].include?(reflection.macro) && reflection.options[:through]
-                @aliased_join_table_name = aliased_table_name_for(reflection.through_reflection.klass.table_name, "_join")
-              end
-            end
-
-            def process_conditions(conditions, table_name)
-              Arel.sql(interpolate_sql(sanitize_sql(conditions, table_name)))
-            end
-
-            def join_target_table(relation, *conditions)
-              relation = relation.join(target_table, join_type)
-
-              # If the target table is an STI model then we must be sure to only include records of
-              # its type and its sub-types.
-              unless active_record.descends_from_active_record?
-                sti_column = target_table[active_record.inheritance_column]
-
-                sti_condition = sti_column.eq(active_record.sti_name)
-                active_record.descendants.each do |subclass|
-                  sti_condition = sti_condition.or(sti_column.eq(subclass.sti_name))
-                end
-
-                conditions << sti_condition
-              end
-
-              # If the reflection has conditions, add them
-              if options[:conditions]
-                conditions << process_conditions(options[:conditions], aliased_table_name)
-              end
-
-              relation = relation.on(*conditions)
-            end
-
-            def join_has_and_belongs_to_many_to(relation)
-              join_table = Arel::Table.new(
-                options[:join_table], :engine => arel_engine,
-                :as => @aliased_join_table_name
-              )
-
-              fk       = options[:foreign_key]             || reflection.active_record.to_s.foreign_key
-              klass_fk = options[:association_foreign_key] || reflection.klass.to_s.foreign_key
-
-              relation = relation.join(join_table, join_type)
-              relation = relation.on(
-                join_table[fk].
-                  eq(parent_table[reflection.active_record.primary_key])
-              )
-
-              join_target_table(
-                relation,
-                target_table[reflection.klass.primary_key].
-                  eq(join_table[klass_fk])
-              )
-            end
-
-            def join_has_many_to(relation)
-              if reflection.options[:through]
-                join_has_many_through_to(relation)
-              elsif reflection.options[:as]
-                join_has_many_polymorphic_to(relation)
-              else
-                foreign_key = options[:foreign_key] || reflection.active_record.name.foreign_key
-                primary_key = options[:primary_key] || parent.primary_key
-
-                join_target_table(
-                  relation,
-                  target_table[foreign_key].
-                    eq(parent_table[primary_key])
-                )
-              end
-            end
-            alias :join_has_one_to :join_has_many_to
-
-            def join_has_many_through_to(relation)
-              join_table = Arel::Table.new(
-                through_reflection.klass.table_name, :engine => arel_engine,
-                :as => @aliased_join_table_name
-              )
-
-              jt_conditions = []
-              jt_foreign_key = first_key = second_key = nil
-
-              if through_reflection.options[:as] # has_many :through against a polymorphic join
-                as_key         = through_reflection.options[:as].to_s
-                jt_foreign_key = as_key + '_id'
-
-                jt_conditions <<
-                  join_table[as_key + '_type'].
-                    eq(parent.active_record.base_class.name)
-              else
-                jt_foreign_key = through_reflection.primary_key_name
-              end
-
-              case source_reflection.macro
-              when :has_many
-                second_key = options[:foreign_key] || primary_key
-
-                if source_reflection.options[:as]
-                  first_key = "#{source_reflection.options[:as]}_id"
-                else
-                  first_key = through_reflection.klass.base_class.to_s.foreign_key
-                end
-
-                unless through_reflection.klass.descends_from_active_record?
-                  jt_conditions <<
-                    join_table[through_reflection.active_record.inheritance_column].
-                      eq(through_reflection.klass.sti_name)
-                end
-              when :belongs_to
-                first_key = primary_key
-
-                if reflection.options[:source_type]
-                  second_key = source_reflection.association_foreign_key
-
-                  jt_conditions <<
-                    join_table[reflection.source_reflection.options[:foreign_type]].
-                      eq(reflection.options[:source_type])
-                else
-                  second_key = source_reflection.primary_key_name
-                end
-              end
-
-              jt_conditions <<
-                parent_table[parent.primary_key].
-                  eq(join_table[jt_foreign_key])
-
-              if through_reflection.options[:conditions]
-                jt_conditions << process_conditions(through_reflection.options[:conditions], aliased_table_name)
-              end
-
-              relation = relation.join(join_table, join_type).on(*jt_conditions)
-
-              join_target_table(
-                relation,
-                target_table[first_key].eq(join_table[second_key])
-              )
-            end
-
-            def join_has_many_polymorphic_to(relation)
-              join_target_table(
-                relation,
-                target_table["#{reflection.options[:as]}_id"].
-                  eq(parent_table[parent.primary_key]),
-                target_table["#{reflection.options[:as]}_type"].
-                  eq(parent.active_record.base_class.name)
-              )
-            end
-
-            def join_belongs_to_to(relation)
-              foreign_key = options[:foreign_key] || reflection.primary_key_name
-              primary_key = options[:primary_key] || reflection.klass.primary_key
-
-              join_target_table(
-                relation,
-                target_table[primary_key].eq(parent_table[foreign_key])
-              )
-            end
-          end
-        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/associations/association_collection.rb b/activerecord/lib/active_record/associations/association_collection.rb
index 6090376bb8..11a7a725e5 100644
--- a/activerecord/lib/active_record/associations/association_collection.rb
+++ b/activerecord/lib/active_record/associations/association_collection.rb
@@ -102,7 +102,7 @@ module ActiveRecord
 
       def reset
         reset_target!
-        reset_named_scopes_cache!
+        reset_scopes_cache!
         @loaded = false
       end
 
@@ -121,13 +121,13 @@ module ActiveRecord
       # Since << flattens its argument list and inserts each record, +push+ and +concat+ behave identically.
       def <<(*records)
         result = true
-        load_target unless @owner.persisted?
+        load_target if @owner.new_record?
 
         transaction do
           flatten_deeper(records).each do |record|
             raise_on_type_mismatch(record)
             add_record_to_target_with_callbacks(record) do |r|
-              result &&= insert_record(record) if @owner.persisted?
+              result &&= insert_record(record) unless @owner.new_record?
             end
           end
         end
@@ -160,7 +160,7 @@ module ActiveRecord
         load_target
         delete(@target)
         reset_target!
-        reset_named_scopes_cache!
+        reset_scopes_cache!
       end
 
       # Calculate sum using SQL, not Enumerable
@@ -235,12 +235,12 @@ module ActiveRecord
 
       # Removes all records from this association.  Returns +self+ so method calls may be chained.
       def clear
-        return self if length.zero? # forces load_target if it hasn't happened already
-
-        if @reflection.options[:dependent] && @reflection.options[:dependent] == :destroy
-          destroy_all
-        else
-          delete_all
+        unless length.zero? # forces load_target if it hasn't happened already
+          if @reflection.options[:dependent] == :destroy
+            destroy_all
+          else
+            delete_all
+          end
         end
 
         self
@@ -253,7 +253,7 @@ module ActiveRecord
         load_target
         destroy(@target).tap do
           reset_target!
-          reset_named_scopes_cache!
+          reset_scopes_cache!
         end
       end
 
@@ -286,12 +286,12 @@ module ActiveRecord
       # This method is abstract in the sense that it relies on
       # +count_records+, which is a method descendants have to provide.
       def size
-        if !@owner.persisted? || (loaded? && !@reflection.options[:uniq])
+        if @owner.new_record? || (loaded? && !@reflection.options[:uniq])
           @target.size
         elsif !loaded? && @reflection.options[:group]
           load_target.size
         elsif !loaded? && !@reflection.options[:uniq] && @target.is_a?(Array)
-          unsaved_records = @target.reject { |r| r.persisted? }
+          unsaved_records = @target.select { |r| r.new_record? }
           unsaved_records.size + count_records
         else
           count_records
@@ -355,10 +355,9 @@ module ActiveRecord
 
       def include?(record)
         return false unless record.is_a?(@reflection.klass)
-        return include_in_memory?(record) unless record.persisted?
+        return include_in_memory?(record) if record.new_record?
         load_target if @reflection.options[:finder_sql] && !loaded?
-        return @target.include?(record) if loaded?
-        exists?(record)
+        loaded? ? @target.include?(record) : exists?(record)
       end
 
       def proxy_respond_to?(method, include_private = false)
@@ -370,7 +369,7 @@ module ActiveRecord
         end
 
         def load_target
-          if @owner.persisted? || foreign_key_present
+          if !@owner.new_record? || foreign_key_present
             begin
               unless loaded?
                 if @target.is_a?(Array) && @target.any?
@@ -410,9 +409,9 @@ module ActiveRecord
           if @target.respond_to?(method) || (!@reflection.klass.respond_to?(method) && Class.respond_to?(method))
             super
           elsif @reflection.klass.scopes[method]
-            @_named_scopes_cache ||= {}
-            @_named_scopes_cache[method] ||= {}
-            @_named_scopes_cache[method][args] ||= with_scope(@scope) { @reflection.klass.send(method, *args) }
+            @_scopes_cache ||= {}
+            @_scopes_cache[method] ||= {}
+            @_scopes_cache[method][args] ||= with_scope(@scope) { @reflection.klass.send(method, *args) }
           else
             with_scope(@scope) do
               if block_given?
@@ -443,8 +442,8 @@ module ActiveRecord
           @target = Array.new
         end
 
-        def reset_named_scopes_cache!
-          @_named_scopes_cache = {}
+        def reset_scopes_cache!
+          @_scopes_cache = {}
         end
 
         def find_target
@@ -479,7 +478,7 @@ module ActiveRecord
       private
         def create_record(attrs)
           attrs.update(@reflection.options[:conditions]) if @reflection.options[:conditions].is_a?(Hash)
-          ensure_owner_is_not_new
+          ensure_owner_is_persisted!
 
           scoped_where = scoped.where_values_hash
           create_scope = scoped_where ? @scope[:create].merge(scoped_where) : @scope[:create]
@@ -509,7 +508,7 @@ module ActiveRecord
 
           transaction do
             records.each { |record| callback(:before_remove, record) }
-            old_records = records.select { |r| r.persisted? }
+            old_records = records.reject { |r| r.new_record? }
             yield(records, old_records)
             records.each { |record| callback(:after_remove, record) }
           end
@@ -530,18 +529,18 @@ module ActiveRecord
 
         def callbacks_for(callback_name)
           full_callback_name = "#{callback_name}_for_#{@reflection.name}"
-          @owner.class.read_inheritable_attribute(full_callback_name.to_sym) || []
+          @owner.class.send(full_callback_name.to_sym) || []
         end
 
-        def ensure_owner_is_not_new
+        def ensure_owner_is_persisted!
           unless @owner.persisted?
             raise ActiveRecord::RecordNotSaved, "You cannot call create unless the parent is saved"
           end
         end
 
         def fetch_first_or_last_using_find?(args)
-          (args.first.kind_of?(Hash) && !args.first.empty?) || !(loaded? || !@owner.persisted? || @reflection.options[:finder_sql] ||
-                                         !@target.all? { |record| record.persisted? } || args.first.kind_of?(Integer))
+          (args.first.kind_of?(Hash) && !args.first.empty?) || !(loaded? || @owner.new_record? || @reflection.options[:finder_sql] ||
+            @target.any? { |record| record.new_record? } || args.first.kind_of?(Integer))
         end
 
         def include_in_memory?(record)
diff --git a/activerecord/lib/active_record/associations/association_proxy.rb b/activerecord/lib/active_record/associations/association_proxy.rb
index 9a9ffe9d62..53ec5a0da6 100644
--- a/activerecord/lib/active_record/associations/association_proxy.rb
+++ b/activerecord/lib/active_record/associations/association_proxy.rb
@@ -253,7 +253,7 @@ module ActiveRecord
         def load_target
           return nil unless defined?(@loaded)
 
-          if !loaded? and (@owner.persisted? || foreign_key_present)
+          if !loaded? && (!@owner.new_record? || foreign_key_present)
             if IdentityMap.enabled? && association_class
               @target = IdentityMap.get(association_class, @owner[@reflection.association_foreign_key])
             end
diff --git a/activerecord/lib/active_record/associations/belongs_to_association.rb b/activerecord/lib/active_record/associations/belongs_to_association.rb
index b624951cd9..b438620c8f 100644
--- a/activerecord/lib/active_record/associations/belongs_to_association.rb
+++ b/activerecord/lib/active_record/associations/belongs_to_association.rb
@@ -61,7 +61,7 @@ module ActiveRecord
           set_inverse_instance(the_target, @owner)
           the_target
         end
-        
+
         def construct_find_scope
           { :conditions => conditions }
         end
diff --git a/activerecord/lib/active_record/associations/class_methods/join_dependency.rb b/activerecord/lib/active_record/associations/class_methods/join_dependency.rb
new file mode 100644
index 0000000000..a74d0a4ca8
--- /dev/null
+++ b/activerecord/lib/active_record/associations/class_methods/join_dependency.rb
@@ -0,0 +1,232 @@
+require 'active_record/associations/class_methods/join_dependency/join_part'
+require 'active_record/associations/class_methods/join_dependency/join_base'
+require 'active_record/associations/class_methods/join_dependency/join_association'
+
+module ActiveRecord
+  module Associations
+    module ClassMethods
+      class JoinDependency # :nodoc:
+        attr_reader :join_parts, :reflections, :table_aliases, :active_record
+
+        def initialize(base, associations, joins)
+          @active_record         = base
+          @table_joins           = joins
+          @join_parts            = [JoinBase.new(base)]
+          @associations          = {}
+          @reflections           = []
+          @table_aliases         = Hash.new do |h,name|
+            h[name] = count_aliases_from_table_joins(name.downcase)
+          end
+          @table_aliases[base.table_name] = 1
+          build(associations)
+        end
+
+        def graft(*associations)
+          associations.each do |association|
+            join_associations.detect {|a| association == a} ||
+              build(association.reflection.name, association.find_parent_in(self) || join_base, association.join_type)
+          end
+          self
+        end
+
+        def join_associations
+          join_parts.last(join_parts.length - 1)
+        end
+
+        def join_base
+          join_parts.first
+        end
+
+        def columns
+          join_parts.collect { |join_part|
+            table = join_part.aliased_table
+            join_part.column_names_with_alias.collect{ |column_name, aliased_name|
+              table[column_name].as Arel.sql(aliased_name)
+            }
+          }.flatten
+        end
+
+        def count_aliases_from_table_joins(name)
+          return 0 if Arel::Table === @table_joins
+
+          # quoted_name should be downcased as some database adapters (Oracle) return quoted name in uppercase
+          quoted_name = active_record.connection.quote_table_name(name).downcase
+
+          @table_joins.map { |join|
+            # Table names + table aliases
+            join.left.downcase.scan(
+              /join(?:\s+\w+)?\s+(\S+\s+)?#{quoted_name}\son/
+            ).size
+          }.sum
+        end
+
+        def instantiate(rows)
+          primary_key = join_base.aliased_primary_key
+          parents = {}
+
+          records = rows.map { |model|
+            primary_id = model[primary_key]
+            parent = parents[primary_id] ||= join_base.instantiate(model)
+            construct(parent, @associations, join_associations, model)
+            parent
+          }.uniq
+
+          remove_duplicate_results!(active_record, records, @associations)
+          records
+        end
+
+        def remove_duplicate_results!(base, records, associations)
+          case associations
+          when Symbol, String
+            reflection = base.reflections[associations]
+            remove_uniq_by_reflection(reflection, records)
+          when Array
+            associations.each do |association|
+              remove_duplicate_results!(base, records, association)
+            end
+          when Hash
+            associations.keys.each do |name|
+              reflection = base.reflections[name]
+              remove_uniq_by_reflection(reflection, records)
+
+              parent_records = []
+              records.each do |record|
+                if descendant = record.send(reflection.name)
+                  if reflection.collection?
+                    parent_records.concat descendant.target.uniq
+                  else
+                    parent_records << descendant
+                  end
+                end
+              end
+
+              remove_duplicate_results!(reflection.klass, parent_records, associations[name]) unless parent_records.empty?
+            end
+          end
+        end
+
+        protected
+
+        def cache_joined_association(association)
+          associations = []
+          parent = association.parent
+          while parent != join_base
+            associations.unshift(parent.reflection.name)
+            parent = parent.parent
+          end
+          ref = @associations
+          associations.each do |key|
+            ref = ref[key]
+          end
+          ref[association.reflection.name] ||= {}
+        end
+
+        def build(associations, parent = nil, join_type = Arel::InnerJoin)
+          parent ||= join_parts.last
+          case associations
+          when Symbol, String
+            reflection = parent.reflections[associations.to_s.intern] or
+            raise ConfigurationError, "Association named '#{ associations }' was not found; perhaps you misspelled it?"
+            unless join_association = find_join_association(reflection, parent)
+              @reflections << reflection
+              join_association = build_join_association(reflection, parent)
+              join_association.join_type = join_type
+              @join_parts << join_association
+              cache_joined_association(join_association)
+            end
+            join_association
+          when Array
+            associations.each do |association|
+              build(association, parent, join_type)
+            end
+          when Hash
+            associations.keys.sort_by { |a| a.to_s }.each do |name|
+              join_association = build(name, parent, join_type)
+              build(associations[name], join_association, join_type)
+            end
+          else
+            raise ConfigurationError, associations.inspect
+          end
+        end
+
+        def find_join_association(name_or_reflection, parent)
+          if String === name_or_reflection
+            name_or_reflection = name_or_reflection.to_sym
+          end
+
+          join_associations.detect { |j|
+            j.reflection == name_or_reflection && j.parent == parent
+          }
+        end
+
+        def remove_uniq_by_reflection(reflection, records)
+          if reflection && reflection.collection?
+            records.each { |record| record.send(reflection.name).target.uniq! }
+          end
+        end
+
+        def build_join_association(reflection, parent)
+          JoinAssociation.new(reflection, self, parent)
+        end
+
+        def construct(parent, associations, join_parts, row)
+          case associations
+          when Symbol, String
+            name = associations.to_s
+
+            join_part = join_parts.detect { |j|
+              j.reflection.name.to_s == name &&
+                j.parent_table_name    == parent.class.table_name }
+
+              raise(ConfigurationError, "No such association") unless join_part
+
+              join_parts.delete(join_part)
+              construct_association(parent, join_part, row)
+          when Array
+            associations.each do |association|
+              construct(parent, association, join_parts, row)
+            end
+          when Hash
+            associations.sort_by { |k,_| k.to_s }.each do |name, assoc|
+              association = construct(parent, name, join_parts, row)
+              construct(association, assoc, join_parts, row) if association
+            end
+          else
+            raise ConfigurationError, associations.inspect
+          end
+        end
+
+        def construct_association(record, join_part, row)
+          return if record.id.to_s != join_part.parent.record_id(row).to_s
+
+          macro = join_part.reflection.macro
+          if macro == :has_one
+            return if record.instance_variable_defined?("@#{join_part.reflection.name}")
+            association = join_part.instantiate(row) unless row[join_part.aliased_primary_key].nil?
+            set_target_and_inverse(join_part, association, record)
+          else
+            return if row[join_part.aliased_primary_key].nil?
+            association = join_part.instantiate(row)
+            case macro
+            when :has_many, :has_and_belongs_to_many
+              collection = record.send(join_part.reflection.name)
+              collection.loaded
+              collection.target.push(association)
+              collection.__send__(:set_inverse_instance, association, record)
+            when :belongs_to
+              set_target_and_inverse(join_part, association, record)
+            else
+              raise ConfigurationError, "unknown macro: #{join_part.reflection.macro}"
+            end
+          end
+          association
+        end
+
+        def set_target_and_inverse(join_part, association, record)
+          association_proxy = record.send("set_#{join_part.reflection.name}_target", association)
+          association_proxy.__send__(:set_inverse_instance, association, record)
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/associations/class_methods/join_dependency/join_association.rb b/activerecord/lib/active_record/associations/class_methods/join_dependency/join_association.rb
new file mode 100644
index 0000000000..694778008b
--- /dev/null
+++ b/activerecord/lib/active_record/associations/class_methods/join_dependency/join_association.rb
@@ -0,0 +1,274 @@
+module ActiveRecord
+  module Associations
+    module ClassMethods
+      class JoinDependency # :nodoc:
+        class JoinAssociation < JoinPart # :nodoc:
+          # The reflection of the association represented
+          attr_reader :reflection
+
+          # The JoinDependency object which this JoinAssociation exists within. This is mainly
+          # relevant for generating aliases which do not conflict with other joins which are
+          # part of the query.
+          attr_reader :join_dependency
+
+          # A JoinBase instance representing the active record we are joining onto.
+          # (So in Author.has_many :posts, the Author would be that base record.)
+          attr_reader :parent
+
+          # What type of join will be generated, either Arel::InnerJoin (default) or Arel::OuterJoin
+          attr_accessor :join_type
+
+          # These implement abstract methods from the superclass
+          attr_reader :aliased_prefix, :aliased_table_name
+
+          delegate :options, :through_reflection, :source_reflection, :to => :reflection
+          delegate :table, :table_name, :to => :parent, :prefix => :parent
+
+          def initialize(reflection, join_dependency, parent = nil)
+            reflection.check_validity!
+
+            if reflection.options[:polymorphic]
+              raise EagerLoadPolymorphicError.new(reflection)
+            end
+
+            super(reflection.klass)
+
+            @reflection      = reflection
+            @join_dependency = join_dependency
+            @parent          = parent
+            @join_type       = Arel::InnerJoin
+            @aliased_prefix  = "t#{ join_dependency.join_parts.size }"
+
+            # This must be done eagerly upon initialisation because the alias which is produced
+            # depends on the state of the join dependency, but we want it to work the same way
+            # every time.
+            allocate_aliases
+            @table = Arel::Table.new(
+              table_name, :as => aliased_table_name, :engine => arel_engine
+            )
+          end
+
+          def ==(other)
+            other.class == self.class &&
+              other.reflection == reflection &&
+              other.parent == parent
+          end
+
+          def find_parent_in(other_join_dependency)
+            other_join_dependency.join_parts.detect do |join_part|
+              parent == join_part
+            end
+          end
+
+          def join_to(relation)
+            send("join_#{reflection.macro}_to", relation)
+          end
+
+          def join_relation(joining_relation)
+            self.join_type = Arel::OuterJoin
+            joining_relation.joins(self)
+          end
+
+          attr_reader :table
+          # More semantic name given we are talking about associations
+          alias_method :target_table, :table
+
+          protected
+
+          def aliased_table_name_for(name, suffix = nil)
+            aliases = @join_dependency.table_aliases
+
+            if aliases[name] != 0 # We need an alias
+              connection = active_record.connection
+
+              name = connection.table_alias_for "#{pluralize(reflection.name)}_#{parent_table_name}#{suffix}"
+              table_index = aliases[name] + 1
+              name = name[0, connection.table_alias_length-3] + "_#{table_index}" if table_index > 1
+            end
+
+            aliases[name] += 1
+
+            name
+          end
+
+          def pluralize(table_name)
+            ActiveRecord::Base.pluralize_table_names ? table_name.to_s.pluralize : table_name
+          end
+
+          private
+
+          def allocate_aliases
+            @aliased_table_name = aliased_table_name_for(table_name)
+
+            if reflection.macro == :has_and_belongs_to_many
+              @aliased_join_table_name = aliased_table_name_for(reflection.options[:join_table], "_join")
+            elsif [:has_many, :has_one].include?(reflection.macro) && reflection.options[:through]
+              @aliased_join_table_name = aliased_table_name_for(reflection.through_reflection.klass.table_name, "_join")
+            end
+          end
+
+          def process_conditions(conditions, table_name)
+            Arel.sql(sanitize_sql(conditions, table_name))
+          end
+
+          def sanitize_sql(condition, table_name)
+            active_record.send(:sanitize_sql, condition, table_name)
+          end
+
+          def join_target_table(relation, condition)
+            conditions = [condition]
+
+            # If the target table is an STI model then we must be sure to only include records of
+            # its type and its sub-types.
+            unless active_record.descends_from_active_record?
+              sti_column    = target_table[active_record.inheritance_column]
+              subclasses    = active_record.descendants
+              sti_condition = sti_column.eq(active_record.sti_name)
+
+              conditions << subclasses.inject(sti_condition) { |attr,subclass|
+                attr.or(sti_column.eq(subclass.sti_name))
+              }
+            end
+
+            # If the reflection has conditions, add them
+            if options[:conditions]
+              conditions << process_conditions(options[:conditions], aliased_table_name)
+            end
+
+            ands = relation.create_and(conditions)
+
+            join = relation.create_join(
+              target_table,
+              relation.create_on(ands),
+              join_type)
+
+            relation.from join
+          end
+
+          def join_has_and_belongs_to_many_to(relation)
+            join_table = Arel::Table.new(
+              options[:join_table]
+            ).alias(@aliased_join_table_name)
+
+            fk       = options[:foreign_key]             || reflection.active_record.to_s.foreign_key
+            klass_fk = options[:association_foreign_key] || reflection.klass.to_s.foreign_key
+
+            relation = relation.join(join_table, join_type)
+            relation = relation.on(
+              join_table[fk].
+              eq(parent_table[reflection.active_record.primary_key])
+            )
+
+            join_target_table(
+              relation,
+              target_table[reflection.klass.primary_key].
+              eq(join_table[klass_fk])
+            )
+          end
+
+          def join_has_many_to(relation)
+            if reflection.options[:through]
+              join_has_many_through_to(relation)
+            elsif reflection.options[:as]
+              join_has_many_polymorphic_to(relation)
+            else
+              foreign_key = options[:foreign_key] || reflection.active_record.name.foreign_key
+              primary_key = options[:primary_key] || parent.primary_key
+
+              join_target_table(
+                relation,
+                target_table[foreign_key].
+                eq(parent_table[primary_key])
+              )
+            end
+          end
+          alias :join_has_one_to :join_has_many_to
+
+          def join_has_many_through_to(relation)
+            join_table = Arel::Table.new(
+              through_reflection.klass.table_name
+            ).alias @aliased_join_table_name
+
+            jt_conditions = []
+            jt_foreign_key = first_key = second_key = nil
+
+            if through_reflection.options[:as] # has_many :through against a polymorphic join
+              as_key         = through_reflection.options[:as].to_s
+              jt_foreign_key = as_key + '_id'
+
+              jt_conditions <<
+              join_table[as_key + '_type'].
+                eq(parent.active_record.base_class.name)
+            else
+              jt_foreign_key = through_reflection.primary_key_name
+            end
+
+            case source_reflection.macro
+            when :has_many
+              second_key = options[:foreign_key] || primary_key
+
+              if source_reflection.options[:as]
+                first_key = "#{source_reflection.options[:as]}_id"
+              else
+                first_key = through_reflection.klass.base_class.to_s.foreign_key
+              end
+
+              unless through_reflection.klass.descends_from_active_record?
+                jt_conditions <<
+                join_table[through_reflection.active_record.inheritance_column].
+                  eq(through_reflection.klass.sti_name)
+              end
+            when :belongs_to
+              first_key = primary_key
+
+              if reflection.options[:source_type]
+                second_key = source_reflection.association_foreign_key
+
+                jt_conditions <<
+                join_table[reflection.source_reflection.options[:foreign_type]].
+                  eq(reflection.options[:source_type])
+              else
+                second_key = source_reflection.primary_key_name
+              end
+            end
+
+            jt_conditions <<
+            parent_table[parent.primary_key].
+              eq(join_table[jt_foreign_key])
+
+            if through_reflection.options[:conditions]
+              jt_conditions << process_conditions(through_reflection.options[:conditions], aliased_table_name)
+            end
+
+            relation = relation.join(join_table, join_type).on(*jt_conditions)
+
+            join_target_table(
+              relation,
+              target_table[first_key].eq(join_table[second_key])
+            )
+          end
+
+          def join_has_many_polymorphic_to(relation)
+            join_target_table(
+              relation,
+              target_table["#{reflection.options[:as]}_id"].
+              eq(parent_table[parent.primary_key]).and(
+              target_table["#{reflection.options[:as]}_type"].
+              eq(parent.active_record.base_class.name))
+            )
+          end
+
+          def join_belongs_to_to(relation)
+            foreign_key = options[:foreign_key] || reflection.primary_key_name
+            primary_key = options[:primary_key] || reflection.klass.primary_key
+
+            join_target_table(
+              relation,
+              target_table[primary_key].eq(parent_table[foreign_key])
+            )
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/associations/class_methods/join_dependency/join_base.rb b/activerecord/lib/active_record/associations/class_methods/join_dependency/join_base.rb
new file mode 100644
index 0000000000..67567f06df
--- /dev/null
+++ b/activerecord/lib/active_record/associations/class_methods/join_dependency/join_base.rb
@@ -0,0 +1,26 @@
+module ActiveRecord
+  module Associations
+    module ClassMethods
+      class JoinDependency # :nodoc:
+        class JoinBase < JoinPart # :nodoc:
+          def ==(other)
+            other.class == self.class &&
+              other.active_record == active_record
+          end
+
+          def aliased_prefix
+            "t0"
+          end
+
+          def table
+            Arel::Table.new(table_name, arel_engine)
+          end
+
+          def aliased_table_name
+            active_record.table_name
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/associations/class_methods/join_dependency/join_part.rb b/activerecord/lib/active_record/associations/class_methods/join_dependency/join_part.rb
new file mode 100644
index 0000000000..cd16ae5a8b
--- /dev/null
+++ b/activerecord/lib/active_record/associations/class_methods/join_dependency/join_part.rb
@@ -0,0 +1,80 @@
+module ActiveRecord
+  module Associations
+    module ClassMethods
+      class JoinDependency # :nodoc:
+        # A JoinPart represents a part of a JoinDependency. It is an abstract class, inherited
+        # by JoinBase and JoinAssociation. A JoinBase represents the Active Record which
+        # everything else is being joined onto. A JoinAssociation represents an association which
+        # is joining to the base. A JoinAssociation may result in more than one actual join
+        # operations (for example a has_and_belongs_to_many JoinAssociation would result in
+        # two; one for the join table and one for the target table).
+        class JoinPart # :nodoc:
+          # The Active Record class which this join part is associated 'about'; for a JoinBase
+          # this is the actual base model, for a JoinAssociation this is the target model of the
+          # association.
+          attr_reader :active_record
+
+          delegate :table_name, :column_names, :primary_key, :reflections, :arel_engine, :to => :active_record
+
+          def initialize(active_record)
+            @active_record = active_record
+            @cached_record = {}
+            @column_names_with_alias = nil
+          end
+
+          def aliased_table
+            Arel::Nodes::TableAlias.new aliased_table_name, table
+          end
+
+          def ==(other)
+            raise NotImplementedError
+          end
+
+          # An Arel::Table for the active_record
+          def table
+            raise NotImplementedError
+          end
+
+          # The prefix to be used when aliasing columns in the active_record's table
+          def aliased_prefix
+            raise NotImplementedError
+          end
+
+          # The alias for the active_record's table
+          def aliased_table_name
+            raise NotImplementedError
+          end
+
+          # The alias for the primary key of the active_record's table
+          def aliased_primary_key
+            "#{aliased_prefix}_r0"
+          end
+
+          # An array of [column_name, alias] pairs for the table
+          def column_names_with_alias
+            unless @column_names_with_alias
+              @column_names_with_alias = []
+
+              ([primary_key] + (column_names - [primary_key])).each_with_index do |column_name, i|
+                @column_names_with_alias << [column_name, "#{aliased_prefix}_r#{i}"]
+              end
+            end
+            @column_names_with_alias
+          end
+
+          def extract_record(row)
+            Hash[column_names_with_alias.map{|cn, an| [cn, row[an]]}]
+          end
+
+          def record_id(row)
+            row[aliased_primary_key]
+          end
+
+          def instantiate(row)
+            @cached_record[record_id(row)] ||= active_record.send(:instantiate, extract_record(row))
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/associations/has_and_belongs_to_many_association.rb b/activerecord/lib/active_record/associations/has_and_belongs_to_many_association.rb
index da742fa668..e2ce9aefcf 100644
--- a/activerecord/lib/active_record/associations/has_and_belongs_to_many_association.rb
+++ b/activerecord/lib/active_record/associations/has_and_belongs_to_many_association.rb
@@ -34,7 +34,7 @@ module ActiveRecord
         end
 
         def insert_record(record, force = true, validate = true)
-          unless record.persisted?
+          if record.new_record?
             if force
               record.save!
             else
@@ -49,7 +49,7 @@ module ActiveRecord
             timestamps = record_timestamp_columns(record)
             timezone   = record.send(:current_time_from_proper_timezone) if timestamps.any?
 
-            attributes = Hash[columns.map do |column|
+            attributes = columns.map do |column|
               name = column.name
               value = case name.to_s
                 when @reflection.primary_key_name.to_s
@@ -62,12 +62,13 @@ module ActiveRecord
                   @owner.send(:quote_value, record[name], column) if record.has_attribute?(name)
               end
               [relation[name], value] unless value.nil?
-            end]
+            end
 
-            relation.insert(attributes)
+            stmt = relation.compile_insert Hash[attributes]
+            @owner.connection.insert stmt.to_sql
           end
 
-          return true
+          true
         end
 
         def delete_records(records)
@@ -75,12 +76,13 @@ module ActiveRecord
             records.each { |record| @owner.connection.delete(interpolate_sql(sql, record)) }
           else
             relation = Arel::Table.new(@reflection.options[:join_table])
-            relation.where(relation[@reflection.primary_key_name].eq(@owner.id).
+            stmt = relation.where(relation[@reflection.primary_key_name].eq(@owner.id).
               and(relation[@reflection.association_foreign_key].in(records.map { |x| x.id }.compact))
-            ).delete
+            ).compile_delete
+            @owner.connection.delete stmt.to_sql
           end
         end
-        
+
         def construct_joins
           "INNER JOIN #{@owner.connection.quote_table_name @reflection.options[:join_table]} ON #{@reflection.quoted_table_name}.#{@reflection.klass.primary_key} = #{@owner.connection.quote_table_name @reflection.options[:join_table]}.#{@reflection.association_foreign_key}"
         end
@@ -113,7 +115,7 @@ module ActiveRecord
       private
         def create_record(attributes, &block)
           # Can't use Base.create because the foreign key may be a protected attribute.
-          ensure_owner_is_not_new
+          ensure_owner_is_persisted!
           if attributes.is_a?(Array)
             attributes.collect { |attr| create(attr) }
           else
diff --git a/activerecord/lib/active_record/associations/has_many_association.rb b/activerecord/lib/active_record/associations/has_many_association.rb
index 830a82980d..4ff61fff45 100644
--- a/activerecord/lib/active_record/associations/has_many_association.rb
+++ b/activerecord/lib/active_record/associations/has_many_association.rb
@@ -42,11 +42,7 @@ module ActiveRecord
           # documented side-effect of the method that may avoid an extra SELECT.
           @target ||= [] and loaded if count == 0
 
-          if @reflection.options[:limit]
-            count = [ @reflection.options[:limit], count ].min
-          end
-
-          return count
+          [@reflection.options[:limit], count].compact.min
         end
 
         def has_cached_counter?
@@ -71,9 +67,10 @@ module ActiveRecord
               @reflection.klass.delete(records.map { |record| record.id })
             else
               relation = Arel::Table.new(@reflection.table_name)
-              relation.where(relation[@reflection.primary_key_name].eq(@owner.id).
+              stmt = relation.where(relation[@reflection.primary_key_name].eq(@owner.id).
                   and(relation[@reflection.klass.primary_key].in(records.map { |r| r.id }))
-              ).update(relation[@reflection.primary_key_name] => nil)
+              ).compile_update(relation[@reflection.primary_key_name] => nil)
+              @owner.connection.update stmt.to_sql
 
               @owner.class.update_counters(@owner.id, cached_counter_attribute_name => -records.size) if has_cached_counter?
           end
@@ -112,8 +109,7 @@ module ActiveRecord
         end
 
         def we_can_set_the_inverse_on_this?(record)
-          inverse = @reflection.inverse_of
-          return !inverse.nil?
+          @reflection.inverse_of
         end
     end
   end
diff --git a/activerecord/lib/active_record/associations/has_many_through_association.rb b/activerecord/lib/active_record/associations/has_many_through_association.rb
index 79c229d9c4..781aa7ef62 100644
--- a/activerecord/lib/active_record/associations/has_many_through_association.rb
+++ b/activerecord/lib/active_record/associations/has_many_through_association.rb
@@ -36,7 +36,7 @@ module ActiveRecord
 
       protected
         def create_record(attrs, force = true)
-          ensure_owner_is_not_new
+          ensure_owner_is_persisted!
 
           transaction do
             object = @reflection.klass.new(attrs)
@@ -54,12 +54,12 @@ module ActiveRecord
         end
 
         def construct_find_options!(options)
-          options[:joins]   = construct_joins(options[:joins])
+          options[:joins]   = [construct_joins] + Array.wrap(options[:joins])
           options[:include] = @reflection.source_reflection.options[:include] if options[:include].nil? && @reflection.source_reflection.options[:include]
         end
 
         def insert_record(record, force = true, validate = true)
-          unless record.persisted?
+          if record.new_record?
             if force
               record.save!
             else
@@ -81,7 +81,7 @@ module ActiveRecord
 
         def find_target
           return [] unless target_reflection_has_associated_record?
-          with_scope(@scope) { @reflection.klass.find(:all) }
+          scoped.all
         end
 
         def has_cached_counter?
diff --git a/activerecord/lib/active_record/associations/has_one_association.rb b/activerecord/lib/active_record/associations/has_one_association.rb
index e6e037441f..c49fd6e66a 100644
--- a/activerecord/lib/active_record/associations/has_one_association.rb
+++ b/activerecord/lib/active_record/associations/has_one_association.rb
@@ -56,7 +56,7 @@ module ActiveRecord
         set_inverse_instance(obj, @owner)
         @loaded = true
 
-        unless !@owner.persisted? or obj.nil? or dont_save
+        unless !@owner.persisted? || obj.nil? || dont_save
           return (obj.save ? self : false)
         else
           return (obj.nil? ? nil : self)
diff --git a/activerecord/lib/active_record/associations/has_one_through_association.rb b/activerecord/lib/active_record/associations/has_one_through_association.rb
index 6e98f7dffb..e8cf73976b 100644
--- a/activerecord/lib/active_record/associations/has_one_through_association.rb
+++ b/activerecord/lib/active_record/associations/has_one_through_association.rb
@@ -21,7 +21,7 @@ module ActiveRecord
         if current_object
            new_value ? current_object.update_attributes(construct_join_attributes(new_value)) : current_object.destroy
         elsif new_value
-          unless @owner.persisted?
+          if @owner.new_record?
             self.target = new_value
             through_association = @owner.send(:association_instance_get, @reflection.through_reflection.name)
             through_association.build(construct_join_attributes(new_value))
@@ -33,7 +33,7 @@ module ActiveRecord
 
     private
       def find_target
-        with_scope(@scope) { @reflection.klass.find(:first) }
+        scoped.first
       end
     end
   end
diff --git a/activerecord/lib/active_record/associations/through_association_scope.rb b/activerecord/lib/active_record/associations/through_association_scope.rb
index bd8e304e99..5dc5b0c048 100644
--- a/activerecord/lib/active_record/associations/through_association_scope.rb
+++ b/activerecord/lib/active_record/associations/through_association_scope.rb
@@ -3,6 +3,13 @@ module ActiveRecord
   module Associations
     module ThroughAssociationScope
 
+      def scoped
+        with_scope(@scope) do
+          @reflection.klass.scoped &
+          @reflection.through_reflection.klass.scoped
+        end
+      end
+
       protected
 
       def construct_find_scope
@@ -16,32 +23,38 @@ module ActiveRecord
           :readonly   => @reflection.options[:readonly]
         }
       end
-      
+
       def construct_create_scope
         construct_owner_attributes(@reflection)
       end
 
+      def aliased_through_table
+        name = @reflection.through_reflection.table_name
+
+        @reflection.table_name == name ?
+          @reflection.through_reflection.klass.arel_table.alias(name + "_join") :
+          @reflection.through_reflection.klass.arel_table
+      end
+
       # Build SQL conditions from attributes, qualified by table name.
       def construct_conditions
-        table_name = @reflection.through_reflection.quoted_table_name
-        conditions = construct_quoted_owner_attributes(@reflection.through_reflection).map do |attr, value|
-          "#{table_name}.#{attr} = #{value}"
+        table = aliased_through_table
+        conditions = construct_owner_attributes(@reflection.through_reflection).map do |attr, value|
+          table[attr].eq(value)
         end
-        conditions << sql_conditions if sql_conditions
-        "(" + conditions.join(') AND (') + ")"
+        conditions << Arel.sql(sql_conditions) if sql_conditions
+        table.create_and(conditions)
       end
 
-      # Associate attributes pointing to owner, quoted.
-      def construct_quoted_owner_attributes(reflection)
+      # Associate attributes pointing to owner
+      def construct_owner_attributes(reflection)
         if as = reflection.options[:as]
-          { "#{as}_id" => owner_quoted_id,
-            "#{as}_type" => reflection.klass.quote_value(
-              @owner.class.base_class.name.to_s,
-              reflection.klass.columns_hash["#{as}_type"]) }
+          { "#{as}_id"   => @owner[reflection.active_record_primary_key],
+            "#{as}_type" => @owner.class.base_class.name }
         elsif reflection.macro == :belongs_to
-          { reflection.klass.primary_key => @owner.class.quote_value(@owner[reflection.primary_key_name]) }
+          { reflection.klass.primary_key => @owner[reflection.primary_key_name] }
         else
-          { reflection.primary_key_name => owner_quoted_id }
+          { reflection.primary_key_name => @owner[reflection.active_record_primary_key] }
         end
       end
 
@@ -51,47 +64,41 @@ module ActiveRecord
 
       def construct_select(custom_select = nil)
         distinct = "DISTINCT " if @reflection.options[:uniq]
-        selected = custom_select || @reflection.options[:select] || "#{distinct}#{@reflection.quoted_table_name}.*"
+        custom_select || @reflection.options[:select] || "#{distinct}#{@reflection.quoted_table_name}.*"
       end
 
-      def construct_joins(custom_joins = nil)
-        polymorphic_join = nil
+      def construct_joins
+        right = aliased_through_table
+        left  = @reflection.klass.arel_table
+
+        conditions = []
+
         if @reflection.source_reflection.macro == :belongs_to
-          reflection_primary_key = @reflection.klass.primary_key
+          reflection_primary_key = @reflection.source_reflection.options[:primary_key] ||
+                                   @reflection.klass.primary_key
           source_primary_key     = @reflection.source_reflection.primary_key_name
           if @reflection.options[:source_type]
-            polymorphic_join = "AND %s.%s = %s" % [
-              @reflection.through_reflection.quoted_table_name, "#{@reflection.source_reflection.options[:foreign_type]}",
-              @owner.class.quote_value(@reflection.options[:source_type])
-            ]
+            column = @reflection.source_reflection.options[:foreign_type]
+            conditions <<
+              right[column].eq(@reflection.options[:source_type])
           end
         else
           reflection_primary_key = @reflection.source_reflection.primary_key_name
-          source_primary_key     = @reflection.through_reflection.klass.primary_key
+          source_primary_key     = @reflection.source_reflection.options[:primary_key] ||
+                                   @reflection.through_reflection.klass.primary_key
           if @reflection.source_reflection.options[:as]
-            polymorphic_join = "AND %s.%s = %s" % [
-              @reflection.quoted_table_name, "#{@reflection.source_reflection.options[:as]}_type",
-              @owner.class.quote_value(@reflection.through_reflection.klass.name)
-            ]
+            column = "#{@reflection.source_reflection.options[:as]}_type"
+            conditions <<
+              left[column].eq(@reflection.through_reflection.klass.name)
           end
         end
 
-        "INNER JOIN %s ON %s.%s = %s.%s %s #{@reflection.options[:joins]} #{custom_joins}" % [
-          @reflection.through_reflection.quoted_table_name,
-          @reflection.quoted_table_name, reflection_primary_key,
-          @reflection.through_reflection.quoted_table_name, source_primary_key,
-          polymorphic_join
-        ]
-      end
+        conditions <<
+          left[reflection_primary_key].eq(right[source_primary_key])
 
-      # Construct attributes for associate pointing to owner.
-      def construct_owner_attributes(reflection)
-        if as = reflection.options[:as]
-          { "#{as}_id" => @owner.id,
-            "#{as}_type" => @owner.class.base_class.name.to_s }
-        else
-          { reflection.primary_key_name => @owner.id }
-        end
+        right.create_join(
+          right,
+          right.create_on(right.create_and(conditions)))
       end
 
       # Construct attributes for :through pointing to owner and associate.
@@ -102,7 +109,7 @@ module ActiveRecord
         join_attributes = construct_owner_attributes(@reflection.through_reflection).merge(@reflection.source_reflection.primary_key_name => associate.id)
 
         if @reflection.options[:source_type]
-          join_attributes.merge!(@reflection.source_reflection.options[:foreign_type] => associate.class.base_class.name.to_s)
+          join_attributes.merge!(@reflection.source_reflection.options[:foreign_type] => associate.class.base_class.name)
         end
 
         if @reflection.through_reflection.options[:conditions].is_a?(Hash)
diff --git a/activerecord/lib/active_record/attribute_methods.rb b/activerecord/lib/active_record/attribute_methods.rb
index 67f70c434e..4f4a0a5fee 100644
--- a/activerecord/lib/active_record/attribute_methods.rb
+++ b/activerecord/lib/active_record/attribute_methods.rb
@@ -54,7 +54,7 @@ module ActiveRecord
 
     protected
       def attribute_method?(attr_name)
-        attr_name == 'id' || @attributes.include?(attr_name)
+        attr_name == 'id' || (defined?(@attributes) && @attributes.include?(attr_name))
       end
   end
 end
diff --git a/activerecord/lib/active_record/attribute_methods/before_type_cast.rb b/activerecord/lib/active_record/attribute_methods/before_type_cast.rb
index 23195b02f7..bde11d0494 100644
--- a/activerecord/lib/active_record/attribute_methods/before_type_cast.rb
+++ b/activerecord/lib/active_record/attribute_methods/before_type_cast.rb
@@ -13,18 +13,19 @@ module ActiveRecord
 
       # Returns a hash of attributes before typecasting and deserialization.
       def attributes_before_type_cast
-        Hash[attribute_names.map { |name| [name, read_attribute_before_type_cast(name)] }]
+        @attributes
       end
 
       private
-        # Handle *_before_type_cast for method_missing.
-        def attribute_before_type_cast(attribute_name)
-          if attribute_name == 'id'
-            read_attribute_before_type_cast(self.class.primary_key)
-          else
-            read_attribute_before_type_cast(attribute_name)
-          end
+
+      # Handle *_before_type_cast for method_missing.
+      def attribute_before_type_cast(attribute_name)
+        if attribute_name == 'id'
+          read_attribute_before_type_cast(self.class.primary_key)
+        else
+          read_attribute_before_type_cast(attribute_name)
         end
+      end
     end
   end
 end
diff --git a/activerecord/lib/active_record/attribute_methods/dirty.rb b/activerecord/lib/active_record/attribute_methods/dirty.rb
index 40ab37b5d2..3eff3d54e3 100644
--- a/activerecord/lib/active_record/attribute_methods/dirty.rb
+++ b/activerecord/lib/active_record/attribute_methods/dirty.rb
@@ -1,3 +1,4 @@
+require 'active_support/core_ext/class/attribute'
 require 'active_support/core_ext/object/blank'
 
 module ActiveRecord
@@ -93,7 +94,7 @@ module ActiveRecord
       end
 
       def clone_with_time_zone_conversion_attribute?(attr, old)
-        old.class.name == "Time" && time_zone_aware_attributes && !skip_time_zone_conversion_for_attributes.include?(attr.to_sym)
+        old.class.name == "Time" && time_zone_aware_attributes && !self.skip_time_zone_conversion_for_attributes.include?(attr.to_sym)
       end
     end
   end
diff --git a/activerecord/lib/active_record/attribute_methods/read.rb b/activerecord/lib/active_record/attribute_methods/read.rb
index ad5a3e7562..506f6e878f 100644
--- a/activerecord/lib/active_record/attribute_methods/read.rb
+++ b/activerecord/lib/active_record/attribute_methods/read.rb
@@ -85,7 +85,8 @@ module ActiveRecord
       def _read_attribute(attr_name)
         attr_name = attr_name.to_s
         attr_name = self.class.primary_key if attr_name == 'id'
-        if value = @attributes[attr_name]
+        value = @attributes[attr_name]
+        unless value.nil?
           if column = column_for_attribute(attr_name)
             if unserializable_attribute?(attr_name, column)
               unserialize_attribute(attr_name)
diff --git a/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb b/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb
index d640b26b74..dc2785b6bf 100644
--- a/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb
+++ b/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb
@@ -1,3 +1,5 @@
+require 'active_support/core_ext/class/attribute'
+
 module ActiveRecord
   module AttributeMethods
     module TimeZoneConversion
@@ -7,7 +9,7 @@ module ActiveRecord
         cattr_accessor :time_zone_aware_attributes, :instance_writer => false
         self.time_zone_aware_attributes = false
 
-        class_inheritable_accessor :skip_time_zone_conversion_for_attributes, :instance_writer => false
+        class_attribute :skip_time_zone_conversion_for_attributes, :instance_writer => false
         self.skip_time_zone_conversion_for_attributes = []
       end
 
@@ -54,7 +56,7 @@ module ActiveRecord
 
         private
           def create_time_zone_conversion_attribute?(name, column)
-            time_zone_aware_attributes && !skip_time_zone_conversion_for_attributes.include?(name.to_sym) && [:datetime, :timestamp].include?(column.type)
+            time_zone_aware_attributes && !self.skip_time_zone_conversion_for_attributes.include?(name.to_sym) && [:datetime, :timestamp].include?(column.type)
           end
       end
     end
diff --git a/activerecord/lib/active_record/autosave_association.rb b/activerecord/lib/active_record/autosave_association.rb
index f417587399..863f64eb3a 100644
--- a/activerecord/lib/active_record/autosave_association.rb
+++ b/activerecord/lib/active_record/autosave_association.rb
@@ -89,7 +89,7 @@ module ActiveRecord
   #   post = Post.create(:title => 'ruby rocks')
   #   post.comments.create(:body => 'hello world')
   #   post.comments[0].body = 'hi everyone'
-  #   post.save # => saves both post and comment, with 'hi everyone' as title
+  #   post.save # => saves both post and comment, with 'hi everyone' as body
   #
   # Destroying one of the associated models as part of the parent's save action
   # is as simple as marking it for destruction:
@@ -234,7 +234,7 @@ module ActiveRecord
     # Returns whether or not this record has been changed in any way (including whether
     # any of its nested autosave associations are likewise changed)
     def changed_for_autosave?
-      !persisted? || changed? || marked_for_destruction? || nested_records_changed_for_autosave?
+      new_record? || changed? || marked_for_destruction? || nested_records_changed_for_autosave?
     end
 
     private
@@ -248,7 +248,7 @@ module ActiveRecord
       elsif autosave
         association.target.find_all { |record| record.changed_for_autosave? }
       else
-        association.target.find_all { |record| !record.persisted? }
+        association.target.find_all { |record| record.new_record? }
       end
     end
 
@@ -274,7 +274,7 @@ module ActiveRecord
     # +reflection+.
     def validate_collection_association(reflection)
       if association = association_instance_get(reflection.name)
-        if records = associated_records_to_validate_or_save(association, !persisted?, reflection.options[:autosave])
+        if records = associated_records_to_validate_or_save(association, new_record?, reflection.options[:autosave])
           records.each { |record| association_valid?(reflection, record) }
         end
       end
@@ -303,7 +303,7 @@ module ActiveRecord
     # Is used as a before_save callback to check while saving a collection
     # association whether or not the parent was a new record before saving.
     def before_save_collection_association
-      @new_record_before_save = !persisted?
+      @new_record_before_save = new_record?
       true
     end
 
@@ -326,17 +326,15 @@ module ActiveRecord
 
               if autosave && record.marked_for_destruction?
                 association.destroy(record)
-              elsif autosave != false && (@new_record_before_save || !record.persisted?)
+              elsif autosave != false && (@new_record_before_save || record.new_record?)
                 if autosave
                   saved = association.send(:insert_record, record, false, false)
                 else
                   association.send(:insert_record, record)
                 end
-              elsif autosave
-                saved = record.save(:validate => false)
-              end
 
-              raise ActiveRecord::Rollback if saved == false
+                raise ActiveRecord::Rollback if saved == false
+              end
             end
           rescue
             records.each {|x| IdentityMap.remove(x) } if IdentityMap.enabled?
@@ -365,7 +363,7 @@ module ActiveRecord
           association.destroy
         else
           key = reflection.options[:primary_key] ? send(reflection.options[:primary_key]) : id
-          if autosave != false && (!persisted? || !association.persisted? || association[reflection.primary_key_name] != key || autosave)
+          if autosave != false && (new_record? || association.new_record? || association[reflection.primary_key_name] != key || autosave)
             association[reflection.primary_key_name] = key
             saved = association.save(:validate => !autosave)
             raise ActiveRecord::Rollback if !saved && autosave
@@ -385,7 +383,7 @@ module ActiveRecord
         if autosave && association.marked_for_destruction?
           association.destroy
         elsif autosave != false
-          saved = association.save(:validate => !autosave) if !association.persisted? || autosave
+          saved = association.save(:validate => !autosave) if association.new_record? || (autosave && association.changed_for_autosave?)
 
           if association.updated?
             association_id = association.send(reflection.options[:primary_key] || :id)
diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index 2b8474b6bf..24c87662b8 100644
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -7,7 +7,7 @@ require 'active_support/time'
 require 'active_support/core_ext/class/attribute'
 require 'active_support/core_ext/class/attribute_accessors'
 require 'active_support/core_ext/class/delegating_attributes'
-require 'active_support/core_ext/class/inheritable_attributes'
+require 'active_support/core_ext/class/attribute'
 require 'active_support/core_ext/array/extract_options'
 require 'active_support/core_ext/hash/deep_merge'
 require 'active_support/core_ext/hash/indifferent_access'
@@ -412,7 +412,7 @@ module ActiveRecord #:nodoc:
     self.store_full_sti_class = true
 
     # Stores the default scope for the class
-    class_inheritable_accessor :default_scoping, :instance_writer => false
+    class_attribute :default_scoping, :instance_writer => false
     self.default_scoping = []
 
     # Returns a hash of all the attributes that have been specified for serialization as
@@ -420,6 +420,9 @@ module ActiveRecord #:nodoc:
     class_attribute :serialized_attributes
     self.serialized_attributes = {}
 
+    class_attribute :_attr_readonly, :instance_writer => false
+    self._attr_readonly = []
+
     class << self # Class methods
       delegate :find, :first, :last, :all, :destroy, :destroy_all, :exists?, :delete, :delete_all, :update, :update_all, :to => :scoped
       delegate :find_each, :find_in_batches, :to => :scoped
@@ -504,12 +507,12 @@ module ActiveRecord #:nodoc:
       # Attributes listed as readonly will be used to create a new record but update operations will
       # ignore these fields.
       def attr_readonly(*attributes)
-        write_inheritable_attribute(:attr_readonly, Set.new(attributes.map { |a| a.to_s }) + (readonly_attributes || []))
+        self._attr_readonly = Set.new(attributes.map { |a| a.to_s }) + (self._attr_readonly || [])
       end
 
       # Returns an array of all the attributes that have been specified as readonly.
       def readonly_attributes
-        read_inheritable_attribute(:attr_readonly) || []
+        self._attr_readonly
       end
 
       # If you have an attribute that needs to be saved to the database as an object, and retrieved as the same object,
@@ -724,10 +727,6 @@ module ActiveRecord #:nodoc:
         @arel_engine = @relation = @arel_table = nil
       end
 
-      def reset_column_information_and_inheritable_attributes_for_all_subclasses#:nodoc:
-        descendants.each { |klass| klass.reset_inheritable_attributes; klass.reset_column_information }
-      end
-
       def attribute_method?(attribute)
         super || (table_exists? && column_names.include?(attribute.to_s.sub(/=$/, '')))
       end
@@ -857,8 +856,8 @@ module ActiveRecord #:nodoc:
       #     limit(10) # Fires "SELECT * FROM posts LIMIT 10"
       #   }
       #
-      # It is recommended to use block form of unscoped because chaining unscoped with <tt>named_scope</tt>
-      # does not work. Assuming that <tt>published</tt> is a <tt>named_scope</tt> following two statements are same.
+      # It is recommended to use block form of unscoped because chaining unscoped with <tt>scope</tt>
+      # does not work. Assuming that <tt>published</tt> is a <tt>scope</tt> following two statements are same.
       #
       # Post.unscoped.published
       # Post.published
@@ -1145,7 +1144,8 @@ MSG
         #   Article.create.published # => true
         def default_scope(options = {})
           reset_scoped_methods
-          self.default_scoping << construct_finder_arel(options, default_scoping.pop)
+          default_scoping = self.default_scoping.dup
+          self.default_scoping = default_scoping << construct_finder_arel(options, default_scoping.pop)
         end
 
         def current_scoped_methods #:nodoc:
@@ -1384,7 +1384,7 @@ MSG
       def initialize(attributes = nil)
         @attributes = attributes_from_column_definition
         @attributes_cache = {}
-        @persisted = false
+        @new_record = true
         @readonly = false
         @destroyed = false
         @marked_for_destruction = false
@@ -1401,30 +1401,6 @@ MSG
         result
       end
 
-      # Cloned objects have no id assigned and are treated as new records. Note that this is a "shallow" clone
-      # as it copies the object's attributes only, not its associations. The extent of a "deep" clone is
-      # application specific and is therefore left to the application to implement according to its need.
-      def initialize_copy(other)
-        _run_after_initialize_callbacks if respond_to?(:_run_after_initialize_callbacks)
-        cloned_attributes = other.clone_attributes(:read_attribute_before_type_cast)
-        cloned_attributes.delete(self.class.primary_key)
-
-        @attributes = cloned_attributes
-
-        @changed_attributes = {}
-        attributes_from_column_definition.each do |attr, orig_value|
-          @changed_attributes[attr] = orig_value if field_changed?(attr, orig_value, @attributes[attr])
-        end
-
-        clear_aggregation_cache
-        clear_association_cache
-        @attributes_cache = {}
-        @persisted = false
-        ensure_proper_type
-
-        populate_with_current_scope_attributes
-      end
-
       # Initialize an empty model object from +coder+.  +coder+ must contain
       # the attributes necessary for initializing an empty model object.  For
       # example:
@@ -1439,7 +1415,7 @@ MSG
         @attributes = coder['attributes']
         @attributes_cache, @previously_changed, @changed_attributes = {}, {}, {}
         @readonly = @destroyed = @marked_for_destruction = false
-        @persisted = true
+        @new_record = false
         _run_find_callbacks
         _run_initialize_callbacks
 
@@ -1482,7 +1458,7 @@ MSG
       #   Person.find(5).cache_key  # => "people/5-20071224150000" (updated_at available)
       def cache_key
         case
-        when !persisted?
+        when new_record?
           "#{self.class.model_name.cache_key}/new"
         when timestamp = self[:updated_at]
           "#{self.class.model_name.cache_key}/#{id}-#{timestamp.to_s(:number)}"
@@ -1500,22 +1476,9 @@ MSG
         @attributes.has_key?(attr_name.to_s)
       end
 
-      # Returns an array of names for the attributes available on this object sorted alphabetically.
+      # Returns an array of names for the attributes available on this object.
       def attribute_names
-        @attributes.keys.sort
-      end
-
-      # Returns the value of the attribute identified by <tt>attr_name</tt> after it has been typecast (for example,
-      # "2004-12-12" in a data column is cast to a date object, like Date.new(2004, 12, 12)).
-      # (Alias for the protected read_attribute method).
-      def [](attr_name)
-        read_attribute(attr_name)
-      end
-
-      # Updates the attribute identified by <tt>attr_name</tt> with the specified +value+.
-      # (Alias for the protected write_attribute method).
-      def []=(attr_name, value)
-        write_attribute(attr_name, value)
+        @attributes.keys
       end
 
       # Allows you to set all the attributes at once by passing in a hash with keys
@@ -1558,9 +1521,7 @@ MSG
 
       # Returns a hash of all the attributes with their names as keys and the values of the attributes as values.
       def attributes
-        attrs = {}
-        attribute_names.each { |name| attrs[name] = read_attribute(name) }
-        attrs
+        Hash[@attributes.map { |name, _| [name, read_attribute(name)] }]
       end
 
       # Returns an <tt>#inspect</tt>-like string for the value of the
@@ -1591,8 +1552,7 @@ MSG
       # Returns true if the specified +attribute+ has been set by the user or by a database load and is neither
       # nil nor empty? (the latter only applies to objects that respond to empty?, most notably Strings).
       def attribute_present?(attribute)
-        value = read_attribute(attribute)
-        !value.blank?
+        !read_attribute(attribute).blank?
       end
 
       # Returns the column object for the named attribute.
@@ -1600,7 +1560,7 @@ MSG
         self.class.columns_hash[name.to_s]
       end
 
-      # Returns true if +comparison_object+ is the same exact object, or +comparison_object+ 
+      # Returns true if +comparison_object+ is the same exact object, or +comparison_object+
       # is of the same type and +self+ has an ID and it is equal to +comparison_object.id+.
       #
       # Note that new records are different from any other record by definition, unless the
@@ -1618,7 +1578,7 @@ MSG
 
       # Delegates to ==
       def eql?(comparison_object)
-        self == (comparison_object)
+        self == comparison_object
       end
 
       # Delegates to id in order to allow two records of the same type and id to work with something like:
@@ -1637,11 +1597,42 @@ MSG
         @attributes.frozen?
       end
 
-      # Returns duplicated record with unfreezed attributes.
-      def dup
-        obj = super
-        obj.instance_variable_set('@attributes', @attributes.dup)
-        obj
+      # Backport dup from 1.9 so that initialize_dup() gets called
+      unless Object.respond_to?(:initialize_dup)
+        def dup # :nodoc:
+          copy = super
+          copy.initialize_dup(self)
+          copy
+        end
+      end
+
+      # Duped objects have no id assigned and are treated as new records. Note
+      # that this is a "shallow" copy as it copies the object's attributes
+      # only, not its associations. The extent of a "deep" copy is application
+      # specific and is therefore left to the application to implement according
+      # to its need.
+      # The dup method does not preserve the timestamps (created|updated)_(at|on).
+      def initialize_dup(other)
+        cloned_attributes = other.clone_attributes(:read_attribute_before_type_cast)
+        cloned_attributes.delete(self.class.primary_key)
+
+        @attributes = cloned_attributes
+
+        _run_after_initialize_callbacks if respond_to?(:_run_after_initialize_callbacks)
+
+        @changed_attributes = {}
+        attributes_from_column_definition.each do |attr, orig_value|
+          @changed_attributes[attr] = orig_value if field_changed?(attr, orig_value, @attributes[attr])
+        end
+
+        clear_aggregation_cache
+        clear_association_cache
+        @attributes_cache   = {}
+        @new_record  = true
+
+        ensure_proper_type
+        populate_with_current_scope_attributes
+        clear_timestamp_attributes
       end
 
       # Returns +true+ if the record is read only. Records loaded through joins with piggy-back
@@ -1658,7 +1649,7 @@ MSG
       # Returns the contents of the record as a nicely formatted string.
       def inspect
         attributes_as_nice_string = self.class.column_names.collect { |name|
-          if has_attribute?(name) || !persisted?
+          if has_attribute?(name) || new_record?
             "#{name}: #{attribute_for_inspect(name)}"
           end
         }.compact.join(", ")
@@ -1710,7 +1701,7 @@ MSG
             if include_readonly_attributes || (!include_readonly_attributes && !self.class.readonly_attributes.include?(name))
               value = read_attribute(name)
 
-              if value && self.class.serialized_attributes.key?(name)
+              if !value.nil? && self.class.serialized_attributes.key?(name)
                 value = YAML.dump value
               end
               attrs[self.class.arel_table[name]] = value
@@ -1845,7 +1836,19 @@ MSG
       def populate_with_current_scope_attributes
         if scope = self.class.send(:current_scoped_methods)
           create_with = scope.scope_for_create
-          create_with.each { |att,value| self.respond_to?(:"#{att}=") && self.send("#{att}=", value) } if create_with
+          create_with.each { |att,value|
+            respond_to?(:"#{att}=") && send("#{att}=", value)
+          }
+        end
+      end
+
+      # Clear attributes and changed_attributes
+      def clear_timestamp_attributes
+        %w(created_at created_on updated_at updated_on).each do |attribute_name|
+          if has_attribute?(attribute_name)
+            self[attribute_name] = nil
+            changed_attributes.delete(attribute_name)
+          end
         end
       end
   end
@@ -1870,6 +1873,7 @@ MSG
     include Callbacks, ActiveModel::Observing, Timestamp
     include Associations, AssociationPreload, NamedScope
     include IdentityMap
+    include ActiveModel::SecurePassword
 
     # AutosaveAssociation needs to be included before Transactions, because we want
     # #save_with_autosave_associations to be wrapped inside a transaction.
@@ -1877,6 +1881,17 @@ MSG
     include Aggregations, Transactions, Reflection, Serialization
 
     NilClass.add_whiner(self) if NilClass.respond_to?(:add_whiner)
+
+    # Returns the value of the attribute identified by <tt>attr_name</tt> after it has been typecast (for example,
+    # "2004-12-12" in a data column is cast to a date object, like Date.new(2004, 12, 12)).
+    # (Alias for the protected read_attribute method).
+    alias [] read_attribute
+
+    # Updates the attribute identified by <tt>attr_name</tt> with the specified +value+.
+    # (Alias for the protected write_attribute method).
+    alias []= write_attribute
+
+    public :[], :[]=
   end
 end
 
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb b/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
index ca9314ec99..cffa2387de 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
@@ -1,3 +1,4 @@
+require 'thread'
 require 'monitor'
 require 'set'
 require 'active_support/core_ext/module/synchronization'
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/database_limits.rb b/activerecord/lib/active_record/connection_adapters/abstract/database_limits.rb
index a130c330dd..29ac9341ec 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/database_limits.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/database_limits.rb
@@ -37,9 +37,9 @@ module ActiveRecord
         16
       end
 
-      # the maximum number of elements in an IN (x,y,z) clause
+      # the maximum number of elements in an IN (x,y,z) clause. nil means no limit
       def in_clause_length
-        65535
+        nil
       end
 
       # the maximum length of an SQL query
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
index 4e770c37da..5b9c48bafa 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
@@ -12,7 +12,7 @@ module ActiveRecord
 
       # Truncates a table alias according to the limits of the current adapter.
       def table_alias_for(table_name)
-        table_name[0..table_alias_length-1].gsub(/\./, '_')
+        table_name[0...table_alias_length].gsub(/\./, '_')
       end
 
       # def tables(name = nil) end
@@ -442,12 +442,14 @@ module ActiveRecord
         end
       end
 
-      def assume_migrated_upto_version(version, migrations_path = ActiveRecord::Migrator.migrations_path)
+      def assume_migrated_upto_version(version, migrations_paths = ActiveRecord::Migrator.migrations_paths)
+        migrations_paths = Array.wrap(migrations_paths)
         version = version.to_i
         sm_table = quote_table_name(ActiveRecord::Migrator.schema_migrations_table_name)
 
         migrated = select_values("SELECT version FROM #{sm_table}").map { |v| v.to_i }
-        versions = Dir["#{migrations_path}/[0-9]*_*.rb"].map do |filename|
+        paths = migrations_paths.map {|p| "#{p}/[0-9]*_*.rb" }
+        versions = Dir[*paths].map do |filename|
           filename.split('/').last.split('_').first.to_i
         end
 
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
index ada1560ce2..0282493219 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
@@ -91,11 +91,6 @@ module ActiveRecord
         false
       end
 
-      # Does this adapter restrict the number of ids you can use in a list. Oracle has a limit of 1000.
-      def ids_in_list_limit
-        nil
-      end
-
       # QUOTING ==================================================
 
       # Override to return the quoted table name. Defaults to column quoting.
@@ -209,8 +204,7 @@ module ActiveRecord
 
       protected
 
-        def log(sql, name)
-          name ||= "SQL"
+        def log(sql, name = "SQL")
           @instrumenter.instrument("sql.active_record",
             :sql => sql, :name => name, :connection_id => object_id) do
             yield
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index ccc5085b84..a4b1aa7154 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -404,10 +404,7 @@ module ActiveRecord
       # REFERENTIAL INTEGRITY ====================================
 
       def supports_disable_referential_integrity?() #:nodoc:
-        version = query("SHOW server_version")[0][0].split('.')
-        version[0].to_i >= 8 && version[1].to_i >= 1
-      rescue
-        return false
+        postgresql_version >= 80100
       end
 
       def disable_referential_integrity #:nodoc:
@@ -956,8 +953,12 @@ module ActiveRecord
             else
               # Mimic PGconn.server_version behavior
               begin
-                query('SELECT version()')[0][0] =~ /PostgreSQL (\d+)\.(\d+)\.(\d+)/
-                ($1.to_i * 10000) + ($2.to_i * 100) + $3.to_i
+                if query('SELECT version()')[0][0] =~ /PostgreSQL ([0-9.]+)/
+                  major, minor, tiny = $1.split(".")
+                  (major.to_i * 10000) + (minor.to_i * 100) + tiny.to_i
+                else
+                  0
+                end
               rescue
                 0
               end
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
index 5ca1923d89..c2cd9e8d5e 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
@@ -40,8 +40,7 @@ module ActiveRecord
         if @connection.respond_to?(:encoding)
           @connection.encoding.to_s
         else
-          encoding = @connection.execute('PRAGMA encoding')
-          encoding[0]['encoding']
+          @connection.execute('PRAGMA encoding')[0]['encoding']
         end
       end
 
diff --git a/activerecord/lib/active_record/counter_cache.rb b/activerecord/lib/active_record/counter_cache.rb
index d48ff92b6c..7839f03848 100644
--- a/activerecord/lib/active_record/counter_cache.rb
+++ b/activerecord/lib/active_record/counter_cache.rb
@@ -30,9 +30,10 @@ module ActiveRecord
         reflection   = belongs_to.find { |e| e.class_name == expected_name }
         counter_name = reflection.counter_cache_column
 
-        self.unscoped.where(arel_table[self.primary_key].eq(object.id)).arel.update({
+        stmt = unscoped.where(arel_table[primary_key].eq(object.id)).arel.compile_update({
           arel_table[counter_name] => object.send(association).count
         })
+        connection.update stmt.to_sql
       end
       return true
     end
diff --git a/activerecord/lib/active_record/locking/optimistic.rb b/activerecord/lib/active_record/locking/optimistic.rb
index bf626301f1..e5065de7fb 100644
--- a/activerecord/lib/active_record/locking/optimistic.rb
+++ b/activerecord/lib/active_record/locking/optimistic.rb
@@ -70,7 +70,7 @@ module ActiveRecord
             result[self.class.locking_column] ||= 0
           end
 
-          return result
+          result
         end
 
         def update(attribute_names = @attributes.keys) #:nodoc:
@@ -87,11 +87,13 @@ module ActiveRecord
           begin
             relation = self.class.unscoped
 
-            affected_rows = relation.where(
+            stmt = relation.where(
               relation.table[self.class.primary_key].eq(quoted_id).and(
-                relation.table[self.class.locking_column].eq(quote_value(previous_value))
+                relation.table[lock_col].eq(quote_value(previous_value))
               )
-            ).arel.update(arel_attributes_values(false, false, attribute_names))
+            ).arel.compile_update(arel_attributes_values(false, false, attribute_names))
+
+            affected_rows = connection.update stmt.to_sql
 
             unless affected_rows == 1
               raise ActiveRecord::StaleObjectError, "Attempted to update a stale object: #{self.class.name}"
@@ -110,12 +112,10 @@ module ActiveRecord
           return super unless locking_enabled?
 
           if persisted?
-            lock_col = self.class.locking_column
-            previous_value = send(lock_col).to_i
-
             table = self.class.arel_table
-            predicate = table[self.class.primary_key].eq(id)
-            predicate = predicate.and(table[self.class.locking_column].eq(previous_value))
+            lock_col = self.class.locking_column
+            predicate = table[self.class.primary_key].eq(id).
+              and(table[lock_col].eq(send(lock_col).to_i))
 
             affected_rows = self.class.unscoped.where(predicate).delete_all
 
diff --git a/activerecord/lib/active_record/migration.rb b/activerecord/lib/active_record/migration.rb
index f6321f1499..640111096d 100644
--- a/activerecord/lib/active_record/migration.rb
+++ b/activerecord/lib/active_record/migration.rb
@@ -1,3 +1,5 @@
+require "active_support/core_ext/array/wrap"
+
 module ActiveRecord
   # Exception that can be raised to stop migrations from going backwards.
   class IrreversibleMigration < ActiveRecordError
@@ -511,38 +513,40 @@ module ActiveRecord
 
   class Migrator#:nodoc:
     class << self
-      attr_writer :migrations_path
+      attr_writer :migrations_paths
+      alias :migrations_path= :migrations_paths=
 
-      def migrate(migrations_path, target_version = nil)
+      def migrate(migrations_paths, target_version = nil)
         case
           when target_version.nil?
-            up(migrations_path, target_version)
+            up(migrations_paths, target_version)
           when current_version == 0 && target_version == 0
+            []
           when current_version > target_version
-            down(migrations_path, target_version)
+            down(migrations_paths, target_version)
           else
-            up(migrations_path, target_version)
+            up(migrations_paths, target_version)
         end
       end
 
-      def rollback(migrations_path, steps=1)
-        move(:down, migrations_path, steps)
+      def rollback(migrations_paths, steps=1)
+        move(:down, migrations_paths, steps)
       end
 
-      def forward(migrations_path, steps=1)
-        move(:up, migrations_path, steps)
+      def forward(migrations_paths, steps=1)
+        move(:up, migrations_paths, steps)
       end
 
-      def up(migrations_path, target_version = nil)
-        self.new(:up, migrations_path, target_version).migrate
+      def up(migrations_paths, target_version = nil)
+        self.new(:up, migrations_paths, target_version).migrate
       end
 
-      def down(migrations_path, target_version = nil)
-        self.new(:down, migrations_path, target_version).migrate
+      def down(migrations_paths, target_version = nil)
+        self.new(:down, migrations_paths, target_version).migrate
       end
 
-      def run(direction, migrations_path, target_version)
-        self.new(direction, migrations_path, target_version).run
+      def run(direction, migrations_paths, target_version)
+        self.new(direction, migrations_paths, target_version).run
       end
 
       def schema_migrations_table_name
@@ -568,12 +572,20 @@ module ActiveRecord
         name.table_name rescue "#{ActiveRecord::Base.table_name_prefix}#{name}#{ActiveRecord::Base.table_name_suffix}"
       end
 
+      def migrations_paths
+        @migrations_paths ||= ['db/migrate']
+        # just to not break things if someone uses: migration_path = some_string
+        Array.wrap(@migrations_paths)
+      end
+
       def migrations_path
-        @migrations_path ||= 'db/migrate'
+        migrations_paths.first
       end
 
-      def migrations(path)
-        files = Dir["#{path}/[0-9]*_*.rb"]
+      def migrations(paths)
+        paths = Array.wrap(paths)
+
+        files = Dir[*paths.map { |p| "#{p}/[0-9]*_*.rb" }]
 
         seen = Hash.new false
 
@@ -597,22 +609,22 @@ module ActiveRecord
 
       private
 
-      def move(direction, migrations_path, steps)
-        migrator = self.new(direction, migrations_path)
+      def move(direction, migrations_paths, steps)
+        migrator = self.new(direction, migrations_paths)
         start_index = migrator.migrations.index(migrator.current_migration)
 
         if start_index
           finish = migrator.migrations[start_index + steps]
           version = finish ? finish.version : 0
-          send(direction, migrations_path, version)
+          send(direction, migrations_paths, version)
         end
       end
     end
 
-    def initialize(direction, migrations_path, target_version = nil)
+    def initialize(direction, migrations_paths, target_version = nil)
       raise StandardError.new("This database does not yet support migrations") unless Base.connection.supports_migrations?
       Base.connection.initialize_schema_migrations_table
-      @direction, @migrations_path, @target_version = direction, migrations_path, target_version
+      @direction, @migrations_paths, @target_version = direction, migrations_paths, target_version
     end
 
     def current_version
@@ -647,6 +659,7 @@ module ActiveRecord
       # skip the last migration if we're headed down, but not ALL the way down
       runnable.pop if down? && target
 
+      ran = []
       runnable.each do |migration|
         Base.logger.info "Migrating to #{migration.name} (#{migration.version})" if Base.logger
 
@@ -666,16 +679,18 @@ module ActiveRecord
             migration.migrate(@direction)
             record_version_state_after_migrating(migration.version)
           end
+          ran << migration
         rescue => e
           canceled_msg = Base.connection.supports_ddl_transactions? ? "this and " : ""
           raise StandardError, "An error has occurred, #{canceled_msg}all later migrations canceled:\n\n#{e}", e.backtrace
         end
       end
+      ran
     end
 
     def migrations
       @migrations ||= begin
-        migrations = self.class.migrations(@migrations_path)
+        migrations = self.class.migrations(@migrations_paths)
         down? ? migrations.reverse : migrations
       end
     end
@@ -696,10 +711,12 @@ module ActiveRecord
         @migrated_versions ||= []
         if down?
           @migrated_versions.delete(version)
-          table.where(table["version"].eq(version.to_s)).delete
+          stmt = table.where(table["version"].eq(version.to_s)).compile_delete
+          Base.connection.delete stmt.to_sql
         else
           @migrated_versions.push(version).sort!
-          table.insert table["version"] => version.to_s
+          stmt = table.compile_insert table["version"] => version.to_s
+          Base.connection.insert stmt.to_sql
         end
       end
 
diff --git a/activerecord/lib/active_record/named_scope.rb b/activerecord/lib/active_record/named_scope.rb
index 0b92ba5caa..0f421560f0 100644
--- a/activerecord/lib/active_record/named_scope.rb
+++ b/activerecord/lib/active_record/named_scope.rb
@@ -2,12 +2,18 @@ require 'active_support/core_ext/array'
 require 'active_support/core_ext/hash/except'
 require 'active_support/core_ext/kernel/singleton_class'
 require 'active_support/core_ext/object/blank'
+require 'active_support/core_ext/class/attribute'
 
 module ActiveRecord
   # = Active Record Named \Scopes
   module NamedScope
     extend ActiveSupport::Concern
 
+    included do
+      class_attribute :scopes
+      self.scopes = {}
+    end
+
     module ClassMethods
       # Returns an anonymous \scope.
       #
@@ -33,10 +39,6 @@ module ActiveRecord
         end
       end
 
-      def scopes
-        read_inheritable_attribute(:scopes) || write_inheritable_attribute(:scopes, {})
-      end
-
       # Adds a class method for retrieving and querying objects. A \scope represents a narrowing of a database query,
       # such as <tt>where(:color => :red).select('shirts.*').includes(:washing_instructions)</tt>.
       #
diff --git a/activerecord/lib/active_record/nested_attributes.rb b/activerecord/lib/active_record/nested_attributes.rb
index 9d7c162798..0a073ad6c8 100644
--- a/activerecord/lib/active_record/nested_attributes.rb
+++ b/activerecord/lib/active_record/nested_attributes.rb
@@ -2,6 +2,7 @@ require 'active_support/core_ext/hash/except'
 require 'active_support/core_ext/object/try'
 require 'active_support/core_ext/object/blank'
 require 'active_support/core_ext/hash/indifferent_access'
+require 'active_support/core_ext/class/attribute'
 
 module ActiveRecord
   module NestedAttributes #:nodoc:
@@ -11,7 +12,7 @@ module ActiveRecord
     extend ActiveSupport::Concern
 
     included do
-      class_inheritable_accessor :nested_attributes_options, :instance_writer => false
+      class_attribute :nested_attributes_options, :instance_writer => false
       self.nested_attributes_options = {}
     end
 
@@ -268,7 +269,11 @@ module ActiveRecord
           if reflection = reflect_on_association(association_name)
             reflection.options[:autosave] = true
             add_autosave_association_callbacks(reflection)
+
+            nested_attributes_options = self.nested_attributes_options.dup
             nested_attributes_options[association_name.to_sym] = options
+            self.nested_attributes_options = nested_attributes_options
+
             type = (reflection.collection? ? :collection : :one_to_one)
 
             # def pirate_attributes=(attributes)
@@ -315,11 +320,10 @@ module ActiveRecord
     # update_only is true, and a <tt>:_destroy</tt> key set to a truthy value,
     # then the existing record will be marked for destruction.
     def assign_nested_attributes_for_one_to_one_association(association_name, attributes)
-      options = nested_attributes_options[association_name]
+      options = self.nested_attributes_options[association_name]
       attributes = attributes.with_indifferent_access
-      check_existing_record = (options[:update_only] || !attributes['id'].blank?)
 
-      if check_existing_record && (record = send(association_name)) &&
+      if (options[:update_only] || !attributes['id'].blank?) && (record = send(association_name)) &&
           (options[:update_only] || record.id.to_s == attributes['id'].to_s)
         assign_to_or_mark_for_destruction(record, attributes, options[:allow_destroy]) unless call_reject_if(association_name, attributes)
 
@@ -364,7 +368,7 @@ module ActiveRecord
     #     { :id => '2', :_destroy => true }
     #   ])
     def assign_nested_attributes_for_collection_association(association_name, attributes_collection)
-      options = nested_attributes_options[association_name]
+      options = self.nested_attributes_options[association_name]
 
       unless attributes_collection.is_a?(Hash) || attributes_collection.is_a?(Array)
         raise ArgumentError, "Hash or Array expected, got #{attributes_collection.class.name} (#{attributes_collection.inspect})"
@@ -419,11 +423,8 @@ module ActiveRecord
     # Updates a record with the +attributes+ or marks it for destruction if
     # +allow_destroy+ is +true+ and has_destroy_flag? returns +true+.
     def assign_to_or_mark_for_destruction(record, attributes, allow_destroy)
-      if has_destroy_flag?(attributes) && allow_destroy
-        record.mark_for_destruction
-      else
-        record.attributes = attributes.except(*UNASSIGNABLE_KEYS)
-      end
+      record.attributes = attributes.except(*UNASSIGNABLE_KEYS)
+      record.mark_for_destruction if has_destroy_flag?(attributes) && allow_destroy
     end
 
     # Determines if a hash contains a truthy _destroy key.
@@ -439,7 +440,7 @@ module ActiveRecord
     end
 
     def call_reject_if(association_name, attributes)
-      case callback = nested_attributes_options[association_name][:reject_if]
+      case callback = self.nested_attributes_options[association_name][:reject_if]
       when Symbol
         method(callback).arity == 0 ? send(callback) : send(callback, attributes)
       when Proc
@@ -448,8 +449,7 @@ module ActiveRecord
     end
 
     def raise_nested_attributes_record_not_found(association_name, record_id)
-      reflection = self.class.reflect_on_association(association_name)
-      raise RecordNotFound, "Couldn't find #{reflection.klass.name} with ID=#{record_id} for #{self.class.name} with ID=#{id}"
+      raise RecordNotFound, "Couldn't find #{self.class.reflect_on_association(association_name).klass.name} with ID=#{record_id} for #{self.class.name} with ID=#{id}"
     end
   end
 end
diff --git a/activerecord/lib/active_record/observer.rb b/activerecord/lib/active_record/observer.rb
index 022cf109af..8b011ad9af 100644
--- a/activerecord/lib/active_record/observer.rb
+++ b/activerecord/lib/active_record/observer.rb
@@ -89,51 +89,25 @@ module ActiveRecord
   # singletons and that call instantiates and registers them.
   #
   class Observer < ActiveModel::Observer
-    class_attribute :observed_methods
-    self.observed_methods = [].freeze
-
-    def initialize
-      super
-      observed_descendants.each { |klass| add_observer!(klass) }
-    end
-
-    def self.method_added(method)
-      method = method.to_sym
-
-      if ActiveRecord::Callbacks::CALLBACKS.include?(method)
-        self.observed_methods += [method]
-        self.observed_methods.freeze
-      end
-    end
 
     protected
 
-      def observed_descendants
-        observed_classes.sum([]) { |klass| klass.descendants }
-      end
-
-      def observe_callbacks?
-        self.class.observed_methods.any?
+      def observed_classes
+        klasses = super
+        klasses + klasses.map { |klass| klass.descendants }.flatten
       end
 
       def add_observer!(klass)
         super
-        define_callbacks klass if observe_callbacks?
+        define_callbacks klass
       end
 
       def define_callbacks(klass)
-        existing_methods = klass.instance_methods.map { |m| m.to_sym }
         observer = self
-        observer_name = observer.class.name.underscore.gsub('/', '__')
 
-        self.class.observed_methods.each do |method|
-          callback = :"_notify_#{observer_name}_for_#{method}"
-          unless existing_methods.include? callback
-            klass.send(:define_method, callback) do  # def _notify_user_observer_for_before_save
-              observer.update(method, self)          #   observer.update(:before_save, self)
-            end                                      # end
-            klass.send(method, callback)             # before_save :_notify_user_observer_for_before_save
-          end
+        ActiveRecord::Callbacks::CALLBACKS.each do |callback|
+          next unless respond_to?(callback)
+          klass.send(callback){|record| observer.send(callback, record)}
         end
       end
   end
diff --git a/activerecord/lib/active_record/persistence.rb b/activerecord/lib/active_record/persistence.rb
index 4fce0cbb3f..78e84c73ee 100644
--- a/activerecord/lib/active_record/persistence.rb
+++ b/activerecord/lib/active_record/persistence.rb
@@ -4,7 +4,7 @@ module ActiveRecord
     # Returns true if this object hasn't been saved yet -- that is, a record
     # for the object doesn't exist in the data store yet; otherwise, returns false.
     def new_record?
-      !@persisted
+      @new_record
     end
 
     # Returns true if this object has been destroyed, otherwise returns false.
@@ -15,7 +15,7 @@ module ActiveRecord
     # Returns if the record is persisted, i.e. it's not a new record and it was
     # not destroyed.
     def persisted?
-      @persisted && !destroyed?
+      !(new_record? || destroyed?)
     end
 
     # Saves the model.
@@ -98,7 +98,7 @@ module ActiveRecord
       became = klass.new
       became.instance_variable_set("@attributes", @attributes)
       became.instance_variable_set("@attributes_cache", @attributes_cache)
-      became.instance_variable_set("@persisted", persisted?)
+      became.instance_variable_set("@new_record", new_record?)
       became.instance_variable_set("@destroyed", destroyed?)
       became.type = klass.name unless self.class.descends_from_active_record?
       became
@@ -250,7 +250,7 @@ module ActiveRecord
   private
     def create_or_update
       raise ReadOnlyRecord if readonly?
-      result = persisted? ? update : create
+      result = new_record? ? create : update
       result != false
     end
 
@@ -259,7 +259,9 @@ module ActiveRecord
     def update(attribute_names = @attributes.keys)
       attributes_with_values = arel_attributes_values(false, false, attribute_names)
       return 0 if attributes_with_values.empty?
-      self.class.unscoped.where(self.class.arel_table[self.class.primary_key].eq(id)).arel.update(attributes_with_values)
+      klass = self.class
+      stmt = klass.unscoped.where(klass.arel_table[klass.primary_key].eq(id)).arel.compile_update(attributes_with_values)
+      klass.connection.update stmt.to_sql
     end
 
     # Creates a record with values matching those of the instance attributes
@@ -280,7 +282,7 @@ module ActiveRecord
       self.id ||= new_id
 
       IdentityMap.add(self) if IdentityMap.enabled?
-      @persisted = true
+      @new_record = false
       id
     end
 
diff --git a/activerecord/lib/active_record/railtie.rb b/activerecord/lib/active_record/railtie.rb
index 9ffc3501c5..a634153d6f 100644
--- a/activerecord/lib/active_record/railtie.rb
+++ b/activerecord/lib/active_record/railtie.rb
@@ -74,11 +74,9 @@ module ActiveRecord
     end
 
     initializer "active_record.set_dispatch_hooks", :before => :set_clear_dependencies_hook do |app|
-      unless app.config.cache_classes
-        ActiveSupport.on_load(:active_record) do
-          ActionDispatch::Callbacks.after do
-            ActiveRecord::Base.clear_reloadable_connections!
-          end
+      ActiveSupport.on_load(:active_record) do
+        ActionDispatch::Reloader.to_cleanup do
+          ActiveRecord::Base.clear_reloadable_connections!
         end
       end
     end
@@ -87,7 +85,7 @@ module ActiveRecord
       ActiveSupport.on_load(:active_record) do
         instantiate_observers
 
-        ActionDispatch::Callbacks.to_prepare(:activerecord_instantiate_observers) do
+        ActionDispatch::Reloader.to_prepare do
           ActiveRecord::Base.instantiate_observers
         end
       end
diff --git a/activerecord/lib/active_record/railties/databases.rake b/activerecord/lib/active_record/railties/databases.rake
index 1fbc8a1d32..a4fc18148e 100644
--- a/activerecord/lib/active_record/railties/databases.rake
+++ b/activerecord/lib/active_record/railties/databases.rake
@@ -1,8 +1,14 @@
-namespace :db do
+db_namespace = namespace :db do
   task :load_config => :rails_env do
     require 'active_record'
     ActiveRecord::Base.configurations = Rails.application.config.database_configuration
-    ActiveRecord::Migrator.migrations_path = Rails.application.paths["db/migrate"].first
+    ActiveRecord::Migrator.migrations_paths = Rails.application.paths["db/migrate"].to_a
+
+    if defined?(ENGINE_PATH) && engine = Rails::Engine.find(ENGINE_PATH)
+      if engine.paths["db/migrate"].existent
+        ActiveRecord::Migrator.migrations_paths += engine.paths["db/migrate"].to_a
+      end
+    end
   end
 
   namespace :create do
@@ -138,21 +144,21 @@ namespace :db do
 
 
   desc "Migrate the database (options: VERSION=x, VERBOSE=false)."
-  task :migrate => :environment do
+  task :migrate => [:environment, :load_config] do
     ActiveRecord::Migration.verbose = ENV["VERBOSE"] ? ENV["VERBOSE"] == "true" : true
-    ActiveRecord::Migrator.migrate(ActiveRecord::Migrator.migrations_path, ENV["VERSION"] ? ENV["VERSION"].to_i : nil)
-    Rake::Task["db:schema:dump"].invoke if ActiveRecord::Base.schema_format == :ruby
+    ActiveRecord::Migrator.migrate(ActiveRecord::Migrator.migrations_paths, ENV["VERSION"] ? ENV["VERSION"].to_i : nil)
+    db_namespace["schema:dump"].invoke if ActiveRecord::Base.schema_format == :ruby
   end
 
   namespace :migrate do
     # desc  'Rollbacks the database one migration and re migrate up (options: STEP=x, VERSION=x).'
-    task :redo => :environment do
+    task :redo => [:environment, :load_config] do
       if ENV["VERSION"]
-        Rake::Task["db:migrate:down"].invoke
-        Rake::Task["db:migrate:up"].invoke
+        db_namespace["migrate:down"].invoke
+        db_namespace["migrate:up"].invoke
       else
-        Rake::Task["db:rollback"].invoke
-        Rake::Task["db:migrate"].invoke
+        db_namespace["rollback"].invoke
+        db_namespace["migrate"].invoke
       end
     end
 
@@ -160,23 +166,23 @@ namespace :db do
     task :reset => ["db:drop", "db:create", "db:migrate"]
 
     # desc 'Runs the "up" for a given migration VERSION.'
-    task :up => :environment do
+    task :up => [:environment, :load_config] do
       version = ENV["VERSION"] ? ENV["VERSION"].to_i : nil
       raise "VERSION is required" unless version
-      ActiveRecord::Migrator.run(:up, ActiveRecord::Migrator.migrations_path, version)
-      Rake::Task["db:schema:dump"].invoke if ActiveRecord::Base.schema_format == :ruby
+      ActiveRecord::Migrator.run(:up, ActiveRecord::Migrator.migrations_paths, version)
+      db_namespace["schema:dump"].invoke if ActiveRecord::Base.schema_format == :ruby
     end
 
     # desc 'Runs the "down" for a given migration VERSION.'
-    task :down => :environment do
+    task :down => [:environment, :load_config] do
       version = ENV["VERSION"] ? ENV["VERSION"].to_i : nil
       raise "VERSION is required" unless version
-      ActiveRecord::Migrator.run(:down, ActiveRecord::Migrator.migrations_path, version)
-      Rake::Task["db:schema:dump"].invoke if ActiveRecord::Base.schema_format == :ruby
+      ActiveRecord::Migrator.run(:down, ActiveRecord::Migrator.migrations_paths, version)
+      db_namespace["schema:dump"].invoke if ActiveRecord::Base.schema_format == :ruby
     end
 
     desc "Display status of migrations"
-    task :status => :environment do
+    task :status => [:environment, :load_config] do
       config = ActiveRecord::Base.configurations[Rails.env || 'development']
       ActiveRecord::Base.establish_connection(config)
       unless ActiveRecord::Base.connection.table_exists?(ActiveRecord::Migrator.schema_migrations_table_name)
@@ -207,17 +213,17 @@ namespace :db do
   end
 
   desc 'Rolls the schema back to the previous version (specify steps w/ STEP=n).'
-  task :rollback => :environment do
+  task :rollback => [:environment, :load_config] do
     step = ENV['STEP'] ? ENV['STEP'].to_i : 1
-    ActiveRecord::Migrator.rollback(ActiveRecord::Migrator.migrations_path, step)
-    Rake::Task["db:schema:dump"].invoke if ActiveRecord::Base.schema_format == :ruby
+    ActiveRecord::Migrator.rollback(ActiveRecord::Migrator.migrations_paths, step)
+    db_namespace["schema:dump"].invoke if ActiveRecord::Base.schema_format == :ruby
   end
 
   # desc 'Pushes the schema to the next version (specify steps w/ STEP=n).'
-  task :forward => :environment do
+  task :forward => [:environment, :load_config] do
     step = ENV['STEP'] ? ENV['STEP'].to_i : 1
-    ActiveRecord::Migrator.forward(ActiveRecord::Migrator.migrations_path, step)
-    Rake::Task["db:schema:dump"].invoke if ActiveRecord::Base.schema_format == :ruby
+    ActiveRecord::Migrator.forward(ActiveRecord::Migrator.migrations_paths, step)
+    db_namespace["schema:dump"].invoke if ActiveRecord::Base.schema_format == :ruby
   end
 
   # desc 'Drops and recreates the database from db/schema.rb for the current environment and loads the seeds.'
@@ -261,7 +267,7 @@ namespace :db do
   # desc "Raises an error if there are pending migrations"
   task :abort_if_pending_migrations => :environment do
     if defined? ActiveRecord
-      pending_migrations = ActiveRecord::Migrator.new(:up, ActiveRecord::Migrator.migrations_path).pending_migrations
+      pending_migrations = ActiveRecord::Migrator.new(:up, ActiveRecord::Migrator.migrations_paths).pending_migrations
 
       if pending_migrations.any?
         puts "You have #{pending_migrations.size} pending migrations:"
@@ -321,12 +327,12 @@ namespace :db do
 
   namespace :schema do
     desc "Create a db/schema.rb file that can be portably used against any DB supported by AR"
-    task :dump => :environment do
+    task :dump => :load_config do
       require 'active_record/schema_dumper'
       File.open(ENV['SCHEMA'] || "#{Rails.root}/db/schema.rb", "w") do |file|
         ActiveRecord::SchemaDumper.dump(ActiveRecord::Base.connection, file)
       end
-      Rake::Task["db:schema:dump"].reenable
+      db_namespace["schema:dump"].reenable
     end
 
     desc "Load a schema.rb file into the database"
@@ -383,7 +389,7 @@ namespace :db do
     task :load => 'db:test:purge' do
       ActiveRecord::Base.establish_connection(ActiveRecord::Base.configurations['test'])
       ActiveRecord::Schema.verbose = false
-      Rake::Task["db:schema:load"].invoke
+      db_namespace["schema:load"].invoke
     end
 
     # desc "Recreate the test database from the current environment's database schema"
@@ -457,7 +463,7 @@ namespace :db do
     # desc 'Check for pending migrations and load the test schema'
     task :prepare => 'db:abort_if_pending_migrations' do
       if defined?(ActiveRecord) && !ActiveRecord::Base.configurations.blank?
-        Rake::Task[{ :sql  => "db:test:clone_structure", :ruby => "db:test:load" }[ActiveRecord::Base.schema_format]].invoke
+        db_namespace[{ :sql  => "test:clone_structure", :ruby => "test:load" }[ActiveRecord::Base.schema_format]].invoke
       end
     end
   end
@@ -501,7 +507,7 @@ namespace :railties do
         puts "Copied migration #{migration.basename} from #{name}"
       end
 
-      ActiveRecord::Migration.copy( ActiveRecord::Migrator.migrations_path, railties,
+      ActiveRecord::Migration.copy( ActiveRecord::Migrator.migrations_paths.first, railties,
                                     :on_skip => on_skip, :on_copy => on_copy)
     end
   end
diff --git a/activerecord/lib/active_record/reflection.rb b/activerecord/lib/active_record/reflection.rb
index a2260e9a19..b9caa64a0e 100644
--- a/activerecord/lib/active_record/reflection.rb
+++ b/activerecord/lib/active_record/reflection.rb
@@ -1,8 +1,15 @@
+require 'active_support/core_ext/class/attribute'
+
 module ActiveRecord
   # = Active Record Reflection
   module Reflection # :nodoc:
     extend ActiveSupport::Concern
 
+    included do
+      class_attribute :reflections
+      self.reflections = {}
+    end
+
     # Reflection enables to interrogate Active Record classes and objects
     # about their associations and aggregations. This information can,
     # for example, be used in a form builder that takes an Active Record object
@@ -20,18 +27,9 @@ module ActiveRecord
           when :composed_of
             reflection = AggregateReflection.new(macro, name, options, active_record)
         end
-        write_inheritable_hash :reflections, name => reflection
-        reflection
-      end
 
-      # Returns a hash containing all AssociationReflection objects for the current class.
-      # Example:
-      #
-      #   Invoice.reflections
-      #   Account.reflections
-      #
-      def reflections
-        read_inheritable_attribute(:reflections) || write_inheritable_attribute(:reflections, {})
+        self.reflections = self.reflections.merge(name => reflection)
+        reflection
       end
 
       # Returns an array of AggregateReflection objects for all the aggregations in the class.
@@ -207,7 +205,11 @@ module ActiveRecord
       end
 
       def association_foreign_key
-        @association_foreign_key ||= @options[:association_foreign_key] || class_name.foreign_key
+        @association_foreign_key ||= options[:association_foreign_key] || class_name.foreign_key
+      end
+
+      def active_record_primary_key
+        @active_record_primary_key ||= options[:primary_key] || active_record.primary_key
       end
 
       def counter_cache_column
@@ -250,7 +252,7 @@ module ActiveRecord
       end
 
       def has_inverse?
-        !@options[:inverse_of].nil?
+        @options[:inverse_of]
       end
 
       def inverse_of
diff --git a/activerecord/lib/active_record/relation.rb b/activerecord/lib/active_record/relation.rb
index 52d5802ee0..c6943444a4 100644
--- a/activerecord/lib/active_record/relation.rb
+++ b/activerecord/lib/active_record/relation.rb
@@ -11,7 +11,6 @@ module ActiveRecord
     include FinderMethods, Calculations, SpawnMethods, QueryMethods, Batches
 
     delegate :to_xml, :to_yaml, :length, :collect, :map, :each, :all?, :include?, :to => :to_a
-    delegate :insert, :to => :arel
 
     attr_reader :table, :klass, :loaded
     attr_accessor :extensions
@@ -28,6 +27,19 @@ module ActiveRecord
       @extensions = []
     end
 
+    def insert(values)
+      im = arel.compile_insert values
+      im.into @table
+      primary_key_name = @klass.primary_key
+      primary_key_value = Hash === values ? values[primary_key_name] : nil
+
+      @klass.connection.insert(
+        im.to_sql,
+        'SQL',
+        primary_key_name,
+        primary_key_value)
+    end
+
     def new(*args, &block)
       scoping { @klass.new(*args, &block) }
     end
@@ -162,7 +174,8 @@ module ActiveRecord
       else
         # Apply limit and order only if they're both present
         if @limit_value.present? == @order_values.present?
-          arel.update(Arel::SqlLiteral.new(@klass.send(:sanitize_sql_for_assignment, updates)))
+          stmt = arel.compile_update(Arel::SqlLiteral.new(@klass.send(:sanitize_sql_for_assignment, updates)))
+          @klass.connection.update stmt.to_sql
         else
           except(:limit, :order).update_all(updates)
         end
@@ -276,7 +289,14 @@ module ActiveRecord
     # If you need to destroy dependent associations or call your <tt>before_*</tt> or
     # +after_destroy+ callbacks, use the +destroy_all+ method instead.
     def delete_all(conditions = nil)
-      conditions ? where(conditions).delete_all : arel.delete.tap { reset }
+      if conditions
+        where(conditions).delete_all
+      else
+        statement = arel.compile_delete
+        affected = @klass.connection.delete statement.to_sql
+        reset
+        affected
+      end
     end
 
     # Deletes the row with a primary key matching the +id+ argument, using a
@@ -325,24 +345,15 @@ module ActiveRecord
     end
 
     def where_values_hash
-      Hash[@where_values.find_all { |w|
-        w.respond_to?(:operator) && w.operator == :== && w.left.relation.name == table_name
-      }.map { |where|
-        [
-          where.left.name,
-          where.right.respond_to?(:value) ? where.right.value : where.right
-        ]
-      }]
+      equalities = @where_values.grep(Arel::Nodes::Equality).find_all { |node|
+        node.left.relation.name == table_name
+      }
+
+      Hash[equalities.map { |where| [where.left.name, where.right] }]
     end
 
     def scope_for_create
-      @scope_for_create ||= begin
-        if @create_with_value
-          @create_with_value.reverse_merge(where_values_hash)
-        else
-          where_values_hash
-        end
-      end
+      @scope_for_create ||= where_values_hash.merge(@create_with_value || {})
     end
 
     def eager_loading?
@@ -354,7 +365,7 @@ module ActiveRecord
       when Relation
         other.to_sql == to_sql
       when Array
-        to_a == other.to_a
+        to_a == other
       end
     end
 
@@ -362,6 +373,10 @@ module ActiveRecord
       to_a.inspect
     end
 
+    def table_name
+      @klass.table_name
+    end
+
     protected
 
     def method_missing(method, *args, &block)
@@ -382,7 +397,7 @@ module ActiveRecord
 
     def references_eager_loaded_tables?
       # always convert table names to downcase as in Oracle quoted table names are in uppercase
-      joined_tables = (tables_in_string(arel.joins(arel)) + [table.name, table.table_alias]).compact.map{ |t| t.downcase }.uniq
+      joined_tables = (tables_in_string(arel.join_sql) + [table.name, table.table_alias]).compact.map{ |t| t.downcase }.uniq
       (tables_in_string(to_sql) - joined_tables).any?
     end
 
diff --git a/activerecord/lib/active_record/relation/calculations.rb b/activerecord/lib/active_record/relation/calculations.rb
index c8adaddfca..fd45bb24dd 100644
--- a/activerecord/lib/active_record/relation/calculations.rb
+++ b/activerecord/lib/active_record/relation/calculations.rb
@@ -166,7 +166,7 @@ module ActiveRecord
       if operation == "count"
         column_name ||= (select_for_count || :all)
 
-        if arel.joins(arel) =~ /LEFT OUTER/i
+        unless arel.ast.grep(Arel::Nodes::OuterJoin).empty?
           distinct = true
           column_name = @klass.primary_key if column_name == :all
         end
diff --git a/activerecord/lib/active_record/relation/finder_methods.rb b/activerecord/lib/active_record/relation/finder_methods.rb
index 4192456447..8bc28c06cb 100644
--- a/activerecord/lib/active_record/relation/finder_methods.rb
+++ b/activerecord/lib/active_record/relation/finder_methods.rb
@@ -187,7 +187,7 @@ module ActiveRecord
 
     def find_with_associations
       including = (@eager_load_values + @includes_values).uniq
-      join_dependency = ActiveRecord::Associations::ClassMethods::JoinDependency.new(@klass, including, nil)
+      join_dependency = ActiveRecord::Associations::ClassMethods::JoinDependency.new(@klass, including, [])
       rows = construct_relation_for_association_find(join_dependency).to_a
       join_dependency.instantiate(rows)
     rescue ThrowResult
@@ -196,13 +196,13 @@ module ActiveRecord
 
     def construct_relation_for_association_calculations
       including = (@eager_load_values + @includes_values).uniq
-      join_dependency = ActiveRecord::Associations::ClassMethods::JoinDependency.new(@klass, including, arel.joins(arel))
+      join_dependency = ActiveRecord::Associations::ClassMethods::JoinDependency.new(@klass, including, arel.froms.first)
       relation = except(:includes, :eager_load, :preload)
       apply_join_dependency(relation, join_dependency)
     end
 
     def construct_relation_for_association_find(join_dependency)
-      relation = except(:includes, :eager_load, :preload, :select).select(column_aliases(join_dependency))
+      relation = except(:includes, :eager_load, :preload, :select).select(join_dependency.columns)
       apply_join_dependency(relation, join_dependency)
     end
 
@@ -290,7 +290,7 @@ module ActiveRecord
     def find_one(id)
       id = id.id if ActiveRecord::Base === id
 
-      column = primary_key.column
+      column = columns_hash[primary_key.name.to_s]
 
       substitute = connection.substitute_for(column, @bind_values)
       relation = where(primary_key.eq(substitute))
@@ -349,17 +349,8 @@ module ActiveRecord
       end
     end
 
-    def column_aliases(join_dependency)
-      join_dependency.join_parts.collect { |join_part|
-        join_part.column_names_with_alias.collect{ |column_name, aliased_name|
-          "#{connection.quote_table_name join_part.aliased_table_name}.#{connection.quote_column_name column_name} AS #{aliased_name}"
-        }
-      }.flatten.join(", ")
-    end
-
     def using_limitable_reflections?(reflections)
       reflections.none? { |r| r.collection? }
     end
-
   end
 end
diff --git a/activerecord/lib/active_record/relation/predicate_builder.rb b/activerecord/lib/active_record/relation/predicate_builder.rb
index 32c7d08daa..70d84619a1 100644
--- a/activerecord/lib/active_record/relation/predicate_builder.rb
+++ b/activerecord/lib/active_record/relation/predicate_builder.rb
@@ -26,7 +26,7 @@ module ActiveRecord
           when Range, Arel::Relation
             attribute.in(value)
           when ActiveRecord::Base
-            attribute.eq(value.quoted_id)
+            attribute.eq(Arel.sql(value.quoted_id))
           when Class
             # FIXME: I think we need to deprecate this behavior
             attribute.eq(value.name)
diff --git a/activerecord/lib/active_record/relation/query_methods.rb b/activerecord/lib/active_record/relation/query_methods.rb
index 9e7503a60d..0ab55ae864 100644
--- a/activerecord/lib/active_record/relation/query_methods.rb
+++ b/activerecord/lib/active_record/relation/query_methods.rb
@@ -13,7 +13,7 @@ module ActiveRecord
     def includes(*args)
       args.reject! {|a| a.blank? }
 
-      return clone if args.empty?
+      return self if args.empty?
 
       relation = clone
       relation.includes_values = (relation.includes_values + args).flatten.uniq
@@ -21,14 +21,18 @@ module ActiveRecord
     end
 
     def eager_load(*args)
+      return self if args.blank?
+
       relation = clone
-      relation.eager_load_values += args unless args.blank?
+      relation.eager_load_values += args
       relation
     end
 
     def preload(*args)
+      return self if args.blank?
+
       relation = clone
-      relation.preload_values += args unless args.blank?
+      relation.preload_values += args
       relation
     end
 
@@ -43,22 +47,28 @@ module ActiveRecord
     end
 
     def group(*args)
+      return self if args.blank?
+
       relation = clone
-      relation.group_values += args.flatten unless args.blank?
+      relation.group_values += args.flatten
       relation
     end
 
     def order(*args)
+      return self if args.blank?
+
       relation = clone
-      relation.order_values += args.flatten unless args.blank?
+      relation.order_values += args.flatten
       relation
     end
 
     def joins(*args)
+      return self if args.compact.blank?
+
       relation = clone
 
       args.flatten!
-      relation.joins_values += args unless args.blank?
+      relation.joins_values += args
 
       relation
     end
@@ -70,14 +80,18 @@ module ActiveRecord
     end
 
     def where(opts, *rest)
+      return self if opts.blank?
+
       relation = clone
-      relation.where_values += build_where(opts, rest) unless opts.blank?
+      relation.where_values += build_where(opts, rest)
       relation
     end
 
     def having(*args)
+      return self if args.blank?
+
       relation = clone
-      relation.having_values += build_where(*args) unless args.blank?
+      relation.having_values += build_where(*args)
       relation
     end
 
@@ -148,53 +162,50 @@ module ActiveRecord
       @arel ||= build_arel
     end
 
-    def custom_join_sql(*joins)
-      arel = table.select_manager
-
-      joins.each do |join|
-        next if join.blank?
+    def build_arel
+      arel = table.from table
 
-        @implicit_readonly = true
+      build_joins(arel, @joins_values) unless @joins_values.empty?
 
-        case join
-        when Array
-          join = Arel.sql(join.join(' ')) if array_of_strings?(join)
-        when String
-          join = Arel.sql(join)
-        end
+      collapse_wheres(arel, (@where_values - ['']).uniq)
 
-        arel.join(join)
-      end
+      arel.having(*@having_values.uniq.reject{|h| h.blank?}) unless @having_values.empty?
 
-      arel.joins(arel)
-    end
+      arel.take(@limit_value) if @limit_value
+      arel.skip(@offset_value) if @offset_value
 
-    def build_arel
-      arel = table
+      arel.group(*@group_values.uniq.reject{|g| g.blank?}) unless @group_values.empty?
 
-      arel = build_joins(arel, @joins_values) unless @joins_values.empty?
+      arel.order(*@order_values.uniq.reject{|o| o.blank?}) unless @order_values.empty?
 
-      arel = collapse_wheres(arel, (@where_values - ['']).uniq)
+      build_select(arel, @select_values.uniq)
 
-      arel = arel.having(*@having_values.uniq.reject{|h| h.blank?}) unless @having_values.empty?
+      arel.from(@from_value) if @from_value
+      arel.lock(@lock_value) if @lock_value
 
-      arel = arel.take(@limit_value) if @limit_value
-      arel = arel.skip(@offset_value) if @offset_value
+      arel
+    end
 
-      arel = arel.group(*@group_values.uniq.reject{|g| g.blank?}) unless @group_values.empty?
+    private
 
-      arel = arel.order(*@order_values.uniq.reject{|o| o.blank?}) unless @order_values.empty?
+    def custom_join_ast(table, joins)
+      joins = joins.reject { |join| join.blank? }
 
-      arel = build_select(arel, @select_values.uniq)
+      return [] if joins.empty?
 
-      arel = arel.from(@from_value) if @from_value
-      arel = arel.lock(@lock_value) if @lock_value
+      @implicit_readonly = true
 
-      arel
+      joins.map do |join|
+        case join
+        when Array
+          join = Arel.sql(join.join(' ')) if array_of_strings?(join)
+        when String
+          join = Arel.sql(join)
+        end
+        table.create_string_join(join)
+      end
     end
 
-    private
-
     def collapse_wheres(arel, wheres)
       equalities = wheres.grep(Arel::Nodes::Equality)
 
@@ -206,14 +217,13 @@ module ActiveRecord
         test = eqls.inject(eqls.shift) do |memo, expr|
           memo.or(expr)
         end
-        arel = arel.where(test)
+        arel.where(test)
       end
 
       (wheres - equalities).each do |where|
         where = Arel.sql(where) if String === where
-        arel = arel.where(Arel::Nodes::Grouping.new(where))
+        arel.where(Arel::Nodes::Grouping.new(where))
       end
-      arel
     end
 
     def build_where(opts, other = [])
@@ -228,31 +238,54 @@ module ActiveRecord
       end
     end
 
-    def build_joins(relation, joins)
-      association_joins = []
-
-      joins = joins.map {|j| j.respond_to?(:strip) ? j.strip : j}.uniq
-
-      joins.each do |join|
-        association_joins << join if [Hash, Array, Symbol].include?(join.class) && !array_of_strings?(join)
+    def build_joins(manager, joins)
+      buckets = joins.group_by do |join|
+        case join
+        when String
+          'string_join'
+        when Hash, Symbol, Array
+          'association_join'
+        when ActiveRecord::Associations::ClassMethods::JoinDependency::JoinAssociation
+          'stashed_join'
+        when Arel::Nodes::Join
+          'join_node'
+        else
+          raise 'unknown class: %s' % join.class.name
+        end
       end
 
-      stashed_association_joins = joins.grep(ActiveRecord::Associations::ClassMethods::JoinDependency::JoinAssociation)
+      association_joins         = buckets['association_join'] || []
+      stashed_association_joins = buckets['stashed_join'] || []
+      join_nodes                = buckets['join_node'] || []
+      string_joins              = (buckets['string_join'] || []).map { |x|
+        x.strip
+      }.uniq
 
-      non_association_joins = (joins - association_joins - stashed_association_joins)
-      custom_joins = custom_join_sql(*non_association_joins)
+      join_list = custom_join_ast(manager, string_joins)
 
-      join_dependency = ActiveRecord::Associations::ClassMethods::JoinDependency.new(@klass, association_joins, custom_joins)
+      join_dependency = ActiveRecord::Associations::ClassMethods::JoinDependency.new(
+        @klass,
+        association_joins,
+        join_list
+      )
+
+      join_nodes.each do |join|
+        join_dependency.table_aliases[join.left.name.downcase] = 1
+      end
 
       join_dependency.graft(*stashed_association_joins)
 
       @implicit_readonly = true unless association_joins.empty? && stashed_association_joins.empty?
 
+      # FIXME: refactor this to build an AST
       join_dependency.join_associations.each do |association|
-        relation = association.join_to(relation)
+        association.join_to(manager)
       end
 
-      relation.join(custom_joins)
+      manager.join_sources.concat join_nodes.uniq
+      manager.join_sources.concat join_list
+
+      manager
     end
 
     def build_select(arel, selects)
diff --git a/activerecord/lib/active_record/relation/spawn_methods.rb b/activerecord/lib/active_record/relation/spawn_methods.rb
index a61a3bd41c..5acf3ec83a 100644
--- a/activerecord/lib/active_record/relation/spawn_methods.rb
+++ b/activerecord/lib/active_record/relation/spawn_methods.rb
@@ -3,10 +3,11 @@ require 'active_support/core_ext/object/blank'
 module ActiveRecord
   module SpawnMethods
     def merge(r)
-      merged_relation = clone
-      return merged_relation unless r
+      return self unless r
       return to_a & r if r.is_a?(Array)
 
+      merged_relation = clone
+
       Relation::ASSOCIATION_METHODS.each do |method|
         value = r.send(:"#{method}_values")
 
@@ -24,7 +25,7 @@ module ActiveRecord
         merged_relation.send(:"#{method}_values=", merged_relation.send(:"#{method}_values") + value) if value.present?
       end
 
-      merged_relation = merged_relation.joins(r.joins_values)
+      merged_relation.joins_values += r.joins_values
 
       merged_wheres = @where_values + r.where_values
 
diff --git a/activerecord/lib/active_record/schema.rb b/activerecord/lib/active_record/schema.rb
index c6bb5c1961..d815ab05ac 100644
--- a/activerecord/lib/active_record/schema.rb
+++ b/activerecord/lib/active_record/schema.rb
@@ -30,8 +30,8 @@ module ActiveRecord
   # ActiveRecord::Schema is only supported by database adapters that also
   # support migrations, the two features being very similar.
   class Schema < Migration
-    def migrations_path
-      ActiveRecord::Migrator.migrations_path
+    def migrations_paths
+      ActiveRecord::Migrator.migrations_paths
     end
 
     # Eval the given block. All methods available to the current connection
@@ -51,7 +51,7 @@ module ActiveRecord
 
       unless info[:version].blank?
         initialize_schema_migrations_table
-        assume_migrated_upto_version(info[:version], schema.migrations_path)
+        assume_migrated_upto_version(info[:version], schema.migrations_paths)
       end
     end
   end
diff --git a/activerecord/lib/active_record/serializers/xml_serializer.rb b/activerecord/lib/active_record/serializers/xml_serializer.rb
index 15abf8bac7..8c4adf7116 100644
--- a/activerecord/lib/active_record/serializers/xml_serializer.rb
+++ b/activerecord/lib/active_record/serializers/xml_serializer.rb
@@ -226,17 +226,17 @@ module ActiveRecord #:nodoc:
 
     class Attribute < ActiveModel::Serializers::Xml::Serializer::Attribute #:nodoc:
       def compute_type
-        type = @serializable.class.serialized_attributes.has_key?(name) ?
-          super : @serializable.class.columns_hash[name].type
+        klass = @serializable.class
+        type = if klass.serialized_attributes.key?(name)
+                 super
+               elsif klass.columns_hash.key?(name)
+                 klass.columns_hash[name].type
+               else
+                 NilClass
+               end
 
-        case type
-        when :text
-          :string
-        when :time
-          :datetime
-        else
-          type
-        end
+        { :text => :string,
+          :time => :datetime }[type] || type
       end
       protected :compute_type
     end
diff --git a/activerecord/lib/active_record/session_store.rb b/activerecord/lib/active_record/session_store.rb
index ba99800fb2..3400fd6ade 100644
--- a/activerecord/lib/active_record/session_store.rb
+++ b/activerecord/lib/active_record/session_store.rb
@@ -228,7 +228,7 @@ module ActiveRecord
         @session_id     = attributes[:session_id]
         @data           = attributes[:data]
         @marshaled_data = attributes[:marshaled_data]
-        @persisted      = !@marshaled_data.nil?
+        @new_record     = @marshaled_data.nil?
       end
 
       # Lazy-unmarshal session state.
@@ -252,8 +252,8 @@ module ActiveRecord
         marshaled_data = self.class.marshal(data)
         connect        = connection
 
-        unless @persisted
-          @persisted = true
+        if @new_record
+          @new_record = false
           connect.update <<-end_sql, 'Create session'
             INSERT INTO #{table_name} (
               #{connect.quote_column_name(session_id_column)},
@@ -272,7 +272,7 @@ module ActiveRecord
       end
 
       def destroy
-        return unless @persisted
+        return if @new_record
 
         connect = connection
         connect.delete <<-end_sql, 'Destroy session'
diff --git a/activerecord/lib/active_record/timestamp.rb b/activerecord/lib/active_record/timestamp.rb
index 230adf6b2b..2ecbd906bd 100644
--- a/activerecord/lib/active_record/timestamp.rb
+++ b/activerecord/lib/active_record/timestamp.rb
@@ -1,3 +1,5 @@
+require 'active_support/core_ext/class/attribute'
+
 module ActiveRecord
   # = Active Record Timestamp
   #
@@ -29,14 +31,14 @@ module ActiveRecord
     extend ActiveSupport::Concern
 
     included do
-      class_inheritable_accessor :record_timestamps, :instance_writer => false
+      class_attribute :record_timestamps, :instance_writer => false
       self.record_timestamps = true
     end
 
   private
 
     def create #:nodoc:
-      if record_timestamps
+      if self.record_timestamps
         current_time = current_time_from_proper_timezone
 
         all_timestamp_attributes.each do |column|
@@ -61,7 +63,7 @@ module ActiveRecord
     end
 
     def should_record_timestamps?
-      record_timestamps && (!partial_updates? || changed? || (attributes.keys & self.class.serialized_attributes.keys).present?)
+      self.record_timestamps && (!partial_updates? || changed? || (attributes.keys & self.class.serialized_attributes.keys).present?)
     end
 
     def timestamp_attributes_for_update_in_model
diff --git a/activerecord/lib/active_record/transactions.rb b/activerecord/lib/active_record/transactions.rb
index 31e60e123d..de496698f1 100644
--- a/activerecord/lib/active_record/transactions.rb
+++ b/activerecord/lib/active_record/transactions.rb
@@ -11,6 +11,7 @@ module ActiveRecord
     included do
       define_callbacks :commit, :rollback, :terminator => "result == false", :scope => [:kind, :name]
     end
+
     # = Active Record Transactions
     #
     # Transactions are protective blocks where SQL statements are only permanent
@@ -130,7 +131,7 @@ module ActiveRecord
     #
     # +transaction+ calls can be nested. By default, this makes all database
     # statements in the nested transaction block become part of the parent
-    # transaction. For example:
+    # transaction. For example, the following behavior may be surprising:
     #
     #   User.transaction do
     #     User.create(:username => 'Kotori')
@@ -140,12 +141,15 @@ module ActiveRecord
     #     end
     #   end
     #
-    #   User.find(:all)  # => empty
+    # creates both "Kotori" and "Nemu". Reason is the <tt>ActiveRecord::Rollback</tt>
+    # exception in the nested block does not issue a ROLLBACK. Since these exceptions
+    # are captured in transaction blocks, the parent block does not see it and the
+    # real transaction is committed.
     #
-    # It is also possible to requires a sub-transaction by passing
-    # <tt>:requires_new => true</tt>. If anything goes wrong, the
-    # database rolls back to the beginning of the sub-transaction
-    # without rolling back the parent transaction. For example:
+    # In order to get a ROLLBACK for the nested transaction you may ask for a real
+    # sub-transaction by passing <tt>:requires_new => true</tt>. If anything goes wrong,
+    # the database rolls back to the beginning of the sub-transaction without rolling
+    # back the parent transaction. If we add it to the previous example:
     #
     #   User.transaction do
     #     User.create(:username => 'Kotori')
@@ -155,12 +159,12 @@ module ActiveRecord
     #     end
     #   end
     #
-    #   User.find(:all)  # => Returns only Kotori
+    # only "Kotori" is created. (This works on MySQL and PostgreSQL, but not on SQLite3.)
     #
     # Most databases don't support true nested transactions. At the time of
     # writing, the only database that we're aware of that supports true nested
     # transactions, is MS-SQL. Because of this, Active Record emulates nested
-    # transactions by using savepoints. See
+    # transactions by using savepoints on MySQL and PostgreSQL. See
     # http://dev.mysql.com/doc/refman/5.0/en/savepoints.html
     # for more information about savepoints.
     #
@@ -242,7 +246,7 @@ module ActiveRecord
       with_transaction_returning_status { super }
     end
 
-    # Reset id and @persisted if the transaction rolls back.
+    # Reset id and @new_record if the transaction rolls back.
     def rollback_active_record_state!
       remember_transaction_record_state
       yield
@@ -298,9 +302,9 @@ module ActiveRecord
     # Save the new record state and id of a record so it can be restored later if a transaction fails.
     def remember_transaction_record_state #:nodoc
       @_start_transaction_state ||= {}
-      unless @_start_transaction_state.include?(:persisted)
+      unless @_start_transaction_state.include?(:new_record)
         @_start_transaction_state[:id] = id if has_attribute?(self.class.primary_key)
-        @_start_transaction_state[:persisted] = @persisted
+        @_start_transaction_state[:new_record] = @new_record
       end
       unless @_start_transaction_state.include?(:destroyed)
         @_start_transaction_state[:destroyed] = @destroyed
@@ -324,8 +328,8 @@ module ActiveRecord
           restore_state = remove_instance_variable(:@_start_transaction_state)
           if restore_state
             @attributes = @attributes.dup if @attributes.frozen?
-            @persisted = restore_state[:persisted]
-            @destroyed = restore_state[:destroyed]
+            @new_record = restore_state[:new_record]
+            @destroyed  = restore_state[:destroyed]
             if restore_state[:id]
               self.id = restore_state[:id]
             else
@@ -346,11 +350,11 @@ module ActiveRecord
     def transaction_include_action?(action) #:nodoc
       case action
       when :create
-        transaction_record_state(:new_record) || !transaction_record_state(:persisted)
+        transaction_record_state(:new_record)
       when :destroy
         destroyed?
       when :update
-        !(transaction_record_state(:new_record) || !transaction_record_state(:persisted) || destroyed?)
+        !(transaction_record_state(:new_record) || destroyed?)
       end
     end
   end
diff --git a/activerecord/lib/active_record/validations.rb b/activerecord/lib/active_record/validations.rb
index ee45fcdf35..f367315b22 100644
--- a/activerecord/lib/active_record/validations.rb
+++ b/activerecord/lib/active_record/validations.rb
@@ -51,7 +51,7 @@ module ActiveRecord
 
     # Runs all the specified validations and returns true if no errors were added otherwise false.
     def valid?(context = nil)
-      context ||= (persisted? ? :update : :create)
+      context ||= (new_record? ? :create : :update)
       output = super(context)
       errors.empty? && output
     end
diff --git a/activerecord/lib/active_record/validations/uniqueness.rb b/activerecord/lib/active_record/validations/uniqueness.rb
index 3eba7510ac..853808eebf 100644
--- a/activerecord/lib/active_record/validations/uniqueness.rb
+++ b/activerecord/lib/active_record/validations/uniqueness.rb
@@ -14,17 +14,14 @@ module ActiveRecord
 
       def validate_each(record, attribute, value)
         finder_class = find_finder_class_for(record)
-        table = finder_class.unscoped
-
-        table_name   = record.class.quoted_table_name
 
         if value && record.class.serialized_attributes.key?(attribute.to_s)
           value = YAML.dump value
         end
 
-        sql, params  = mount_sql_and_params(finder_class, table_name, attribute, value)
+        sql, params = mount_sql_and_params(finder_class, record.class.quoted_table_name, attribute, value)
 
-        relation = table.where(sql, *params)
+        relation = finder_class.unscoped.where(sql, *params)
 
         Array.wrap(options[:scope]).each do |scope_item|
           scope_value = record.send(scope_item)