Merge branch 'master' into nested_has_many_through

Conflicts:
	activerecord/CHANGELOG
	activerecord/lib/active_record/associations.rb

30 files changed, 1058 insertions, 825 deletions

diff --git a/activerecord/lib/active_record/association_preload.rb b/activerecord/lib/active_record/association_preload.rb
index 8e7416472f..8ca83a7e75 100644
--- a/activerecord/lib/active_record/association_preload.rb
+++ b/activerecord/lib/active_record/association_preload.rb
@@ -193,13 +193,17 @@ module ActiveRecord
         conditions = "t0.#{reflection.primary_key_name} #{in_or_equals_for_ids(ids)}"
         conditions << append_conditions(reflection, preload_options)
 
-        associated_records = reflection.klass.unscoped.where([conditions, ids]).
+        associated_records_proxy = reflection.klass.unscoped.
             includes(options[:include]).
             joins("INNER JOIN #{connection.quote_table_name options[:join_table]} t0 ON #{reflection.klass.quoted_table_name}.#{reflection.klass.primary_key} = t0.#{reflection.association_foreign_key}").
             select("#{options[:select] || table_name+'.*'}, t0.#{reflection.primary_key_name} as the_parent_record_id").
-            order(options[:order]).to_a
+            order(options[:order])
 
-        set_association_collection_records(id_to_record_map, reflection.name, associated_records, 'the_parent_record_id')
+        all_associated_records = associated_records(ids) do |some_ids|
+          associated_records_proxy.where([conditions, ids]).to_a
+        end
+
+        set_association_collection_records(id_to_record_map, reflection.name, all_associated_records, 'the_parent_record_id')
       end
 
       def preload_has_one_or_has_many_association(records, reflection, preload_options={})
@@ -376,13 +380,14 @@ module ActiveRecord
         find_options = {
           :select => preload_options[:select] || options[:select] || Arel::SqlLiteral.new("#{table_name}.*"),
           :include => preload_options[:include] || options[:include],
-          :conditions => [conditions, ids],
           :joins => options[:joins],
           :group => preload_options[:group] || options[:group],
           :order => preload_options[:order] || options[:order]
         }
 
-        reflection.klass.scoped.apply_finder_options(find_options).to_a
+        associated_records(ids) do |some_ids|
+          reflection.klass.scoped.apply_finder_options(find_options.merge(:conditions => [conditions, some_ids])).to_a
+        end
       end
 
 
@@ -400,6 +405,17 @@ module ActiveRecord
       def in_or_equals_for_ids(ids)
         ids.size > 1 ? "IN (?)" : "= ?"
       end
+
+      # 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)
+        in_clause_length = connection.in_clause_length || ids.size
+        records = []
+        ids.each_slice(in_clause_length) do |some_ids|
+          records += yield(some_ids)
+        end
+        records
+      end
     end
   end
 end
diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index e82cbd0aa6..fe22fa7ca2 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:
@@ -1853,12 +1855,12 @@ 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
 
@@ -1874,552 +1876,6 @@ module ActiveRecord
             Array.wrap(extensions)
           end
         end
-
-        class JoinDependency # :nodoc:
-          attr_reader :join_parts, :reflections, :alias_tracker
-
-          def initialize(base, associations, joins)
-            @join_parts            = [JoinBase.new(base, joins)]
-            @associations          = {}
-            @reflections           = []
-            @alias_tracker         = AliasTracker.new(joins)
-            @alias_tracker.aliased_name_for(base.table_name) # Updates the count for base.table_name to 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 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
-
-            attr_reader :aliased_prefix
-
-            delegate :options, :through_reflection, :source_reflection, :through_reflection_chain, :to => :reflection
-            delegate :table, :table_name, :to => :parent, :prefix => true
-            delegate :alias_tracker, :to => :join_dependency
-
-            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 }"
-
-              setup_tables
-            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)
-              # The chain starts with the target table, but we want to end with it here (makes
-              # more sense in this context)
-              chain = through_reflection_chain.reverse
-
-              foreign_table = parent_table
-              index = 0
-
-              chain.each do |reflection|
-                table = @tables[index]
-                conditions = []
-
-                if reflection.source_reflection.nil?
-                  case reflection.macro
-                    when :belongs_to
-                      key         = reflection.association_primary_key
-                      foreign_key = reflection.primary_key_name
-                    when :has_many, :has_one
-                      key         = reflection.primary_key_name
-                      foreign_key = reflection.active_record_primary_key
-
-                      conditions << polymorphic_conditions(reflection, table)
-                    when :has_and_belongs_to_many
-                      # For habtm, we need to deal with the join table at the same time as the
-                      # target table (because unlike a :through association, there is no reflection
-                      # to represent the join table)
-                      table, join_table = table
-
-                      join_key         = reflection.primary_key_name
-                      join_foreign_key = reflection.active_record.primary_key
-
-                      relation = relation.join(join_table, join_type).on(
-                        join_table[join_key].
-                          eq(foreign_table[join_foreign_key])
-                      )
-
-                      # We've done the first join now, so update the foreign_table for the second
-                      foreign_table = join_table
-
-                      key         = reflection.klass.primary_key
-                      foreign_key = reflection.association_foreign_key
-                  end
-                else
-                  case reflection.source_reflection.macro
-                    when :belongs_to
-                      key         = reflection.association_primary_key
-                      foreign_key = reflection.primary_key_name
-
-                      conditions << source_type_conditions(reflection, foreign_table)
-                    when :has_many, :has_one
-                      key         = reflection.primary_key_name
-                      foreign_key = reflection.source_reflection.active_record_primary_key
-                    when :has_and_belongs_to_many
-                      table, join_table = table
-
-                      join_key         = reflection.primary_key_name
-                      join_foreign_key = reflection.klass.primary_key
-
-                      relation = relation.join(join_table, join_type).on(
-                        join_table[join_key].
-                          eq(foreign_table[join_foreign_key])
-                      )
-
-                      foreign_table = join_table
-
-                      key         = reflection.klass.primary_key
-                      foreign_key = reflection.association_foreign_key
-                  end
-                end
-
-                conditions << table[key].eq(foreign_table[foreign_key])
-
-                conditions << reflection_conditions(index, table)
-                conditions << sti_conditions(reflection, table)
-
-                relation = relation.join(table, join_type).on(*conditions.flatten.compact)
-
-                # The current table in this iteration becomes the foreign table in the next
-                foreign_table = table
-                index += 1
-              end
-
-              relation
-            end
-
-            def join_relation(joining_relation)
-              self.join_type = Arel::OuterJoin
-              joining_relation.joins(self)
-            end
-
-            def table
-              if @tables.last.is_a?(Array)
-                @tables.last.first
-              else
-                @tables.last
-              end
-            end
-
-            def aliased_table_name
-              table.table_alias || table.name
-            end
-
-            protected
-
-              def table_alias_for(reflection, join = false)
-                name = alias_tracker.pluralize(reflection.name)
-                name << "_#{parent_table_name}"
-                name << "_join" if join
-                name
-              end
-
-              def interpolate_sql(sql)
-                instance_eval("%@#{sql.gsub('@', '\@')}@", __FILE__, __LINE__)
-              end
-
-            private
-
-            # Generate aliases and Arel::Table instances for each of the tables which we will
-            # later generate joins for. We must do this in advance in order to correctly allocate
-            # the proper alias.
-            def setup_tables
-              @tables = through_reflection_chain.map do |reflection|
-                aliased_table_name = alias_tracker.aliased_name_for(
-                  reflection.table_name,
-                  table_alias_for(reflection, reflection != self.reflection)
-                )
-
-                table = Arel::Table.new(
-                  reflection.table_name, :engine => arel_engine,
-                  :as => aliased_table_name, :columns => reflection.klass.columns
-                )
-
-                # For habtm, we have two Arel::Table instances related to a single reflection, so
-                # we just store them as a pair in the array.
-                if reflection.macro == :has_and_belongs_to_many ||
-                     (reflection.source_reflection &&
-                      reflection.source_reflection.macro == :has_and_belongs_to_many)
-
-                  join_table_name = (reflection.source_reflection || reflection).options[:join_table]
-
-                  aliased_join_table_name = alias_tracker.aliased_name_for(
-                    join_table_name,
-                    table_alias_for(reflection, true)
-                  )
-
-                  join_table = Arel::Table.new(
-                    join_table_name, :engine => arel_engine,
-                    :as => aliased_join_table_name
-                  )
-
-                  [table, join_table]
-                else
-                  table
-                end
-              end
-
-              # The joins are generated from the through_reflection_chain in reverse order, so
-              # reverse the tables too (but it's important to generate the aliases in the 'forward'
-              # order, which is why we only do the reversal now.
-              @tables.reverse!
-
-              @tables
-            end
-
-            def reflection_conditions(index, table)
-              @reflection.through_conditions.reverse[index].map do |condition|
-                Arel.sql(interpolate_sql(sanitize_sql(
-                  condition,
-                  table.table_alias || table.name
-                )))
-              end
-            end
-
-            def sti_conditions(reflection, table)
-              unless reflection.klass.descends_from_active_record?
-                sti_column = table[reflection.klass.inheritance_column]
-
-                condition = sti_column.eq(reflection.klass.sti_name)
-
-                reflection.klass.descendants.each do |subclass|
-                  condition = condition.or(sti_column.eq(subclass.sti_name))
-                end
-
-                condition
-              end
-            end
-
-            def source_type_conditions(reflection, foreign_table)
-              if reflection.options[:source_type]
-                foreign_table[reflection.source_reflection.options[:foreign_type]].
-                  eq(reflection.options[:source_type])
-              end
-           end
-
-           def polymorphic_conditions(reflection, table)
-             if reflection.options[:as]
-               table["#{reflection.options[:as]}_type"].
-                 eq(reflection.active_record.base_class.name)
-             end
-           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..ba9373ba6a 100644
--- a/activerecord/lib/active_record/associations/association_collection.rb
+++ b/activerecord/lib/active_record/associations/association_collection.rb
@@ -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
@@ -357,8 +357,7 @@ module ActiveRecord
         return false unless record.is_a?(@reflection.klass)
         return include_in_memory?(record) unless record.persisted?
         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)
@@ -530,7 +529,7 @@ 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
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..ce20420aad
--- /dev/null
+++ b/activerecord/lib/active_record/associations/class_methods/join_dependency.rb
@@ -0,0 +1,214 @@
+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, :alias_tracker
+
+        def initialize(base, associations, joins)
+          @join_parts            = [JoinBase.new(base, joins)]
+          @associations          = {}
+          @reflections           = []
+          @alias_tracker         = AliasTracker.new(joins)
+          @alias_tracker.aliased_name_for(base.table_name) # Updates the count for base.table_name to 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 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
+      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..ed2053d3df
--- /dev/null
+++ b/activerecord/lib/active_record/associations/class_methods/join_dependency/join_association.rb
@@ -0,0 +1,261 @@
+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
+
+          attr_reader :aliased_prefix
+
+          delegate :options, :through_reflection, :source_reflection, :through_reflection_chain, :to => :reflection
+          delegate :table, :table_name, :to => :parent, :prefix => true
+          delegate :alias_tracker, :to => :join_dependency
+
+          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 }"
+
+            setup_tables
+          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)
+            # The chain starts with the target table, but we want to end with it here (makes
+            # more sense in this context)
+            chain = through_reflection_chain.reverse
+
+            foreign_table = parent_table
+            index = 0
+
+            chain.each do |reflection|
+              table = @tables[index]
+              conditions = []
+
+              if reflection.source_reflection.nil?
+                case reflection.macro
+                  when :belongs_to
+                    key         = reflection.association_primary_key
+                    foreign_key = reflection.primary_key_name
+                  when :has_many, :has_one
+                    key         = reflection.primary_key_name
+                    foreign_key = reflection.active_record_primary_key
+
+                    conditions << polymorphic_conditions(reflection, table)
+                  when :has_and_belongs_to_many
+                    # For habtm, we need to deal with the join table at the same time as the
+                    # target table (because unlike a :through association, there is no reflection
+                    # to represent the join table)
+                    table, join_table = table
+
+                    join_key         = reflection.primary_key_name
+                    join_foreign_key = reflection.active_record.primary_key
+
+                    relation = relation.join(join_table, join_type).on(
+                      join_table[join_key].
+                        eq(foreign_table[join_foreign_key])
+                    )
+
+                    # We've done the first join now, so update the foreign_table for the second
+                    foreign_table = join_table
+
+                    key         = reflection.klass.primary_key
+                    foreign_key = reflection.association_foreign_key
+                end
+              else
+                case reflection.source_reflection.macro
+                  when :belongs_to
+                    key         = reflection.association_primary_key
+                    foreign_key = reflection.primary_key_name
+
+                    conditions << source_type_conditions(reflection, foreign_table)
+                  when :has_many, :has_one
+                    key         = reflection.primary_key_name
+                    foreign_key = reflection.source_reflection.active_record_primary_key
+                  when :has_and_belongs_to_many
+                    table, join_table = table
+
+                    join_key         = reflection.primary_key_name
+                    join_foreign_key = reflection.klass.primary_key
+
+                    relation = relation.join(join_table, join_type).on(
+                      join_table[join_key].
+                        eq(foreign_table[join_foreign_key])
+                    )
+
+                    foreign_table = join_table
+
+                    key         = reflection.klass.primary_key
+                    foreign_key = reflection.association_foreign_key
+                end
+              end
+
+              conditions << table[key].eq(foreign_table[foreign_key])
+
+              conditions << reflection_conditions(index, table)
+              conditions << sti_conditions(reflection, table)
+
+              relation = relation.join(table, join_type).on(*conditions.flatten.compact)
+
+              # The current table in this iteration becomes the foreign table in the next
+              foreign_table = table
+              index += 1
+            end
+
+            relation
+          end
+
+          def join_relation(joining_relation)
+            self.join_type = Arel::OuterJoin
+            joining_relation.joins(self)
+          end
+
+          def table
+            if @tables.last.is_a?(Array)
+              @tables.last.first
+            else
+              @tables.last
+            end
+          end
+
+          def aliased_table_name
+            table.table_alias || table.name
+          end
+
+          protected
+
+          def table_alias_for(reflection, join = false)
+            name = alias_tracker.pluralize(reflection.name)
+            name << "_#{parent_table_name}"
+            name << "_join" if join
+            name
+          end
+
+          def interpolate_sql(sql)
+            instance_eval("%@#{sql.gsub('@', '\@')}@", __FILE__, __LINE__)
+          end
+
+          private
+
+          # Generate aliases and Arel::Table instances for each of the tables which we will
+          # later generate joins for. We must do this in advance in order to correctly allocate
+          # the proper alias.
+          def setup_tables
+            @tables = through_reflection_chain.map do |reflection|
+              aliased_table_name = alias_tracker.aliased_name_for(
+                reflection.table_name,
+                table_alias_for(reflection, reflection != self.reflection)
+              )
+
+              table = Arel::Table.new(
+                reflection.table_name, :engine => arel_engine,
+                :as => aliased_table_name, :columns => reflection.klass.columns
+              )
+
+              # For habtm, we have two Arel::Table instances related to a single reflection, so
+              # we just store them as a pair in the array.
+              if reflection.macro == :has_and_belongs_to_many ||
+                   (reflection.source_reflection &&
+                    reflection.source_reflection.macro == :has_and_belongs_to_many)
+
+                join_table_name = (reflection.source_reflection || reflection).options[:join_table]
+
+                aliased_join_table_name = alias_tracker.aliased_name_for(
+                  join_table_name,
+                  table_alias_for(reflection, true)
+                )
+
+                join_table = Arel::Table.new(
+                  join_table_name, :engine => arel_engine,
+                  :as => aliased_join_table_name
+                )
+
+                [table, join_table]
+              else
+                table
+              end
+            end
+
+            # The joins are generated from the through_reflection_chain in reverse order, so
+            # reverse the tables too (but it's important to generate the aliases in the 'forward'
+            # order, which is why we only do the reversal now.
+            @tables.reverse!
+
+            @tables
+          end
+
+          def reflection_conditions(index, table)
+            @reflection.through_conditions.reverse[index].map do |condition|
+              Arel.sql(interpolate_sql(sanitize_sql(
+                condition,
+                table.table_alias || table.name
+              )))
+            end
+          end
+
+          def sti_conditions(reflection, table)
+            unless reflection.klass.descends_from_active_record?
+              sti_column = table[reflection.klass.inheritance_column]
+
+              condition = sti_column.eq(reflection.klass.sti_name)
+
+              reflection.klass.descendants.each do |subclass|
+                condition = condition.or(sti_column.eq(subclass.sti_name))
+              end
+
+              condition
+            end
+          end
+
+          def source_type_conditions(reflection, foreign_table)
+            if reflection.options[:source_type]
+              foreign_table[reflection.source_reflection.options[:foreign_type]].
+                eq(reflection.options[:source_type])
+            end
+          end
+
+          def polymorphic_conditions(reflection, table)
+            if reflection.options[:as]
+              table["#{reflection.options[:as]}_type"].
+                eq(reflection.active_record.base_class.name)
+            end
+          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..ed05003f66
--- /dev/null
+++ b/activerecord/lib/active_record/associations/class_methods/join_dependency/join_base.rb
@@ -0,0 +1,34 @@
+module ActiveRecord
+  module Associations
+    module ClassMethods
+      class JoinDependency # :nodoc:
+        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
+      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..0b093b65e9
--- /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, :sanitize_sql, :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..2c72fd0004 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
@@ -67,7 +67,7 @@ module ActiveRecord
             relation.insert(attributes)
           end
 
-          return true
+          true
         end
 
         def delete_records(records)
@@ -80,7 +80,7 @@ module ActiveRecord
             ).delete
           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
diff --git a/activerecord/lib/active_record/associations/has_many_association.rb b/activerecord/lib/active_record/associations/has_many_association.rb
index 7eaa05ee36..bbf62796bb 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?
@@ -112,8 +108,7 @@ 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/through_association_scope.rb b/activerecord/lib/active_record/associations/through_association_scope.rb
index 07ce6f1597..f6d02a215f 100644
--- a/activerecord/lib/active_record/associations/through_association_scope.rb
+++ b/activerecord/lib/active_record/associations/through_association_scope.rb
@@ -57,7 +57,7 @@ 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)
diff --git a/activerecord/lib/active_record/attribute_methods/dirty.rb b/activerecord/lib/active_record/attribute_methods/dirty.rb
index 439880c1fa..c19a33faa8 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
@@ -88,7 +89,7 @@ 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/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 cb5bc06580..73ac8e82c6 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:
diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index b35f59d6df..9b09b14c87 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
@@ -736,15 +735,12 @@ module ActiveRecord #:nodoc:
       def lookup_ancestors #:nodoc:
         klass = self
         classes = [klass]
+        return classes if klass == ActiveRecord::Base
+
         while klass != klass.base_class
           classes << klass = klass.superclass
         end
         classes
-      rescue
-        # OPTIMIZE this rescue is to fix this test: ./test/cases/reflection_test.rb:56:in `test_human_name_for_column'
-        # Apparently the method base_class causes some trouble.
-        # It now works for sure.
-        [self]
       end
 
       # Set the i18n scope to overwrite ActiveModel.
@@ -1129,7 +1125,8 @@ 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:
@@ -1286,7 +1283,7 @@ MSG
         #   ["name='%s' and group_id='%s'", "foo'bar", 4]  returns  "name='foo''bar' and group_id='4'"
         def sanitize_sql_array(ary)
           statement, *values = ary
-          if values.first.is_a?(Hash) and statement =~ /:\w+/
+          if values.first.is_a?(Hash) && statement =~ /:\w+/
             replace_named_bind_variables(statement, values.first)
           elsif statement.include?('?')
             replace_bind_variables(statement, values)
@@ -1385,30 +1382,6 @@ 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:
@@ -1573,8 +1546,7 @@ 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.
@@ -1582,7 +1554,7 @@ 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
@@ -1600,7 +1572,7 @@ 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:
@@ -1619,11 +1591,42 @@ 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   = {}
+        @persisted  = false
+
+        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
@@ -1830,6 +1833,16 @@ MSG
           create_with.each { |att,value| self.respond_to?(:"#{att}=") && self.send("#{att}=", value) } if create_with
         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
 
   Base.class_eval do
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_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
index f3fba9a3a9..0282493219 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
@@ -204,8 +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/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/locking/optimistic.rb b/activerecord/lib/active_record/locking/optimistic.rb
index bf626301f1..c0e1dda2bd 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:
@@ -89,7 +89,7 @@ module ActiveRecord
 
             affected_rows = 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))
 
@@ -110,12 +110,10 @@ 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 2c306d233a..f6321f1499 100644
--- a/activerecord/lib/active_record/migration.rb
+++ b/activerecord/lib/active_record/migration.rb
@@ -1,6 +1,3 @@
-require 'active_support/core_ext/kernel/singleton_class'
-require 'active_support/core_ext/module/aliasing'
-
 module ActiveRecord
   # Exception that can be raised to stop migrations from going backwards.
   class IrreversibleMigration < ActiveRecordError
@@ -43,11 +40,11 @@ module ActiveRecord
   # Example of a simple migration:
   #
   #   class AddSsl < ActiveRecord::Migration
-  #     def self.up
+  #     def up
   #       add_column :accounts, :ssl_enabled, :boolean, :default => 1
   #     end
   #
-  #     def self.down
+  #     def down
   #       remove_column :accounts, :ssl_enabled
   #     end
   #   end
@@ -63,7 +60,7 @@ module ActiveRecord
   # Example of a more complex migration that also needs to initialize data:
   #
   #   class AddSystemSettings < ActiveRecord::Migration
-  #     def self.up
+  #     def up
   #       create_table :system_settings do |t|
   #         t.string  :name
   #         t.string  :label
@@ -77,7 +74,7 @@ module ActiveRecord
   #                             :value => 1
   #     end
   #
-  #     def self.down
+  #     def down
   #       drop_table :system_settings
   #     end
   #   end
@@ -138,7 +135,7 @@ module ActiveRecord
   # in the <tt>db/migrate/</tt> directory where <tt>timestamp</tt> is the
   # UTC formatted date and time that the migration was generated.
   #
-  # You may then edit the <tt>self.up</tt> and <tt>self.down</tt> methods of
+  # You may then edit the <tt>up</tt> and <tt>down</tt> methods of
   # MyNewMigration.
   #
   # There is a special syntactic shortcut to generate migrations that add fields to a table.
@@ -147,11 +144,11 @@ module ActiveRecord
   #
   # This will generate the file <tt>timestamp_add_fieldname_to_tablename</tt>, which will look like this:
   #   class AddFieldnameToTablename < ActiveRecord::Migration
-  #     def self.up
+  #     def up
   #       add_column :tablenames, :fieldname, :string
   #     end
   #
-  #     def self.down
+  #     def down
   #       remove_column :tablenames, :fieldname
   #     end
   #   end
@@ -179,11 +176,11 @@ module ActiveRecord
   # Not all migrations change the schema. Some just fix the data:
   #
   #   class RemoveEmptyTags < ActiveRecord::Migration
-  #     def self.up
+  #     def up
   #       Tag.find(:all).each { |tag| tag.destroy if tag.pages.empty? }
   #     end
   #
-  #     def self.down
+  #     def down
   #       # not much we can do to restore deleted data
   #       raise ActiveRecord::IrreversibleMigration, "Can't recover the deleted tags"
   #     end
@@ -192,12 +189,12 @@ module ActiveRecord
   # Others remove columns when they migrate up instead of down:
   #
   #   class RemoveUnnecessaryItemAttributes < ActiveRecord::Migration
-  #     def self.up
+  #     def up
   #       remove_column :items, :incomplete_items_count
   #       remove_column :items, :completed_items_count
   #     end
   #
-  #     def self.down
+  #     def down
   #       add_column :items, :incomplete_items_count
   #       add_column :items, :completed_items_count
   #     end
@@ -206,11 +203,11 @@ module ActiveRecord
   # And sometimes you need to do something in SQL not abstracted directly by migrations:
   #
   #   class MakeJoinUnique < ActiveRecord::Migration
-  #     def self.up
+  #     def up
   #       execute "ALTER TABLE `pages_linked_pages` ADD UNIQUE `page_id_linked_page_id` (`page_id`,`linked_page_id`)"
   #     end
   #
-  #     def self.down
+  #     def down
   #       execute "ALTER TABLE `pages_linked_pages` DROP INDEX `page_id_linked_page_id`"
   #     end
   #   end
@@ -223,7 +220,7 @@ module ActiveRecord
   # latest column data from after the new column was added. Example:
   #
   #   class AddPeopleSalary < ActiveRecord::Migration
-  #     def self.up
+  #     def up
   #       add_column :people, :salary, :integer
   #       Person.reset_column_information
   #       Person.find(:all).each do |p|
@@ -243,7 +240,7 @@ module ActiveRecord
   # You can also insert your own messages and benchmarks by using the +say_with_time+
   # method:
   #
-  #   def self.up
+  #   def up
   #     ...
   #     say_with_time "Updating salaries..." do
   #       Person.find(:all).each do |p|
@@ -286,144 +283,200 @@ module ActiveRecord
   #
   # In application.rb.
   #
+  # == Reversible Migrations
+  #
+  # Starting with Rails 3.1, you will be able to define reversible migrations.
+  # Reversible migrations are migrations that know how to go +down+ for you.
+  # You simply supply the +up+ logic, and the Migration system will figure out
+  # how to execute the down commands for you.
+  #
+  # To define a reversible migration, define the +change+ method in your
+  # migration like this:
+  #
+  #   class TenderloveMigration < ActiveRecord::Migration
+  #     def change
+  #       create_table(:horses) do
+  #         t.column :content, :text
+  #         t.column :remind_at, :datetime
+  #       end
+  #     end
+  #   end
+  #
+  # This migration will create the horses table for you on the way up, and
+  # automatically figure out how to drop the table on the way down.
+  #
+  # Some commands like +remove_column+ cannot be reversed.  If you care to
+  # define how to move up and down in these cases, you should define the +up+
+  # and +down+ methods as before.
+  #
+  # If a command cannot be reversed, an
+  # <tt>ActiveRecord::IrreversibleMigration</tt> exception will be raised when
+  # the migration is moving down.
+  #
+  # For a list of commands that are reversible, please see
+  # <tt>ActiveRecord::Migration::CommandRecorder</tt>.
   class Migration
-    @@verbose = true
-    cattr_accessor :verbose
+    autoload :CommandRecorder, 'active_record/migration/command_recorder'
 
     class << self
-      def up_with_benchmarks #:nodoc:
-        migrate(:up)
-      end
+      attr_accessor :delegate # :nodoc:
+    end
 
-      def down_with_benchmarks #:nodoc:
-        migrate(:down)
-      end
+    def self.method_missing(name, *args, &block) # :nodoc:
+      (delegate || superclass.delegate).send(name, *args, &block)
+    end
 
-      # Execute this migration in the named direction
-      def migrate(direction)
-        return unless respond_to?(direction)
+    cattr_accessor :verbose
 
-        case direction
-          when :up   then announce "migrating"
-          when :down then announce "reverting"
-        end
+    attr_accessor :name, :version
 
-        result = nil
-        time = Benchmark.measure { result = send("#{direction}_without_benchmarks") }
+    def initialize
+      @name       = self.class.name
+      @version    = nil
+      @connection = nil
+    end
 
-        case direction
-          when :up   then announce "migrated (%.4fs)" % time.real; write
-          when :down then announce "reverted (%.4fs)" % time.real; write
-        end
+    # instantiate the delegate object after initialize is defined
+    self.verbose  = true
+    self.delegate = new
 
-        result
-      end
+    def up
+      self.class.delegate = self
+      return unless self.class.respond_to?(:up)
+      self.class.up
+    end
+
+    def down
+      self.class.delegate = self
+      return unless self.class.respond_to?(:down)
+      self.class.down
+    end
 
-      # Because the method added may do an alias_method, it can be invoked
-      # recursively. We use @ignore_new_methods as a guard to indicate whether
-      # it is safe for the call to proceed.
-      def singleton_method_added(sym) #:nodoc:
-        return if defined?(@ignore_new_methods) && @ignore_new_methods
+    # Execute this migration in the named direction
+    def migrate(direction)
+      return unless respond_to?(direction)
 
-        begin
-          @ignore_new_methods = true
+      case direction
+      when :up   then announce "migrating"
+      when :down then announce "reverting"
+      end
 
-          case sym
-            when :up, :down
-              singleton_class.send(:alias_method_chain, sym, "benchmarks")
+      time   = nil
+      ActiveRecord::Base.connection_pool.with_connection do |conn|
+        @connection = conn
+        if respond_to?(:change)
+          if direction == :down
+            recorder = CommandRecorder.new(@connection)
+            suppress_messages do
+              @connection = recorder
+              change
+            end
+            @connection = conn
+            time = Benchmark.measure {
+              recorder.inverse.each do |cmd, args|
+                send(cmd, *args)
+              end
+            }
+          else
+            time = Benchmark.measure { change }
           end
-        ensure
-          @ignore_new_methods = false
+        else
+          time = Benchmark.measure { send(direction) }
         end
+        @connection = nil
       end
 
-      def write(text="")
-        puts(text) if verbose
+      case direction
+      when :up   then announce "migrated (%.4fs)" % time.real; write
+      when :down then announce "reverted (%.4fs)" % time.real; write
       end
+    end
 
-      def announce(message)
-        version = defined?(@version) ? @version : nil
+    def write(text="")
+      puts(text) if verbose
+    end
 
-        text = "#{version} #{name}: #{message}"
-        length = [0, 75 - text.length].max
-        write "== %s %s" % [text, "=" * length]
-      end
+    def announce(message)
+      text = "#{version} #{name}: #{message}"
+      length = [0, 75 - text.length].max
+      write "== %s %s" % [text, "=" * length]
+    end
 
-      def say(message, subitem=false)
-        write "#{subitem ? "   ->" : "--"} #{message}"
-      end
+    def say(message, subitem=false)
+      write "#{subitem ? "   ->" : "--"} #{message}"
+    end
 
-      def say_with_time(message)
-        say(message)
-        result = nil
-        time = Benchmark.measure { result = yield }
-        say "%.4fs" % time.real, :subitem
-        say("#{result} rows", :subitem) if result.is_a?(Integer)
-        result
-      end
+    def say_with_time(message)
+      say(message)
+      result = nil
+      time = Benchmark.measure { result = yield }
+      say "%.4fs" % time.real, :subitem
+      say("#{result} rows", :subitem) if result.is_a?(Integer)
+      result
+    end
 
-      def suppress_messages
-        save, self.verbose = verbose, false
-        yield
-      ensure
-        self.verbose = save
-      end
+    def suppress_messages
+      save, self.verbose = verbose, false
+      yield
+    ensure
+      self.verbose = save
+    end
 
-      def connection
-        ActiveRecord::Base.connection
-      end
+    def connection
+      @connection || ActiveRecord::Base.connection
+    end
 
-      def method_missing(method, *arguments, &block)
-        arg_list = arguments.map{ |a| a.inspect } * ', '
+    def method_missing(method, *arguments, &block)
+      arg_list = arguments.map{ |a| a.inspect } * ', '
 
-        say_with_time "#{method}(#{arg_list})" do
-          unless arguments.empty? || method == :execute
-            arguments[0] = Migrator.proper_table_name(arguments.first)
-          end
-          connection.send(method, *arguments, &block)
+      say_with_time "#{method}(#{arg_list})" do
+        unless arguments.empty? || method == :execute
+          arguments[0] = Migrator.proper_table_name(arguments.first)
         end
+        return super unless connection.respond_to?(method)
+        connection.send(method, *arguments, &block)
       end
+    end
 
-      def copy(destination, sources, options = {})
-        copied = []
+    def copy(destination, sources, options = {})
+      copied = []
 
-        FileUtils.mkdir_p(destination) unless File.exists?(destination)
+      FileUtils.mkdir_p(destination) unless File.exists?(destination)
 
-        destination_migrations = ActiveRecord::Migrator.migrations(destination)
-        last = destination_migrations.last
-        sources.each do |name, path|
-          source_migrations = ActiveRecord::Migrator.migrations(path)
+      destination_migrations = ActiveRecord::Migrator.migrations(destination)
+      last = destination_migrations.last
+      sources.each do |name, path|
+        source_migrations = ActiveRecord::Migrator.migrations(path)
 
-          source_migrations.each do |migration|
-            source = File.read(migration.filename)
-            source = "# This migration comes from #{name} (originally #{migration.version})\n#{source}"
+        source_migrations.each do |migration|
+          source = File.read(migration.filename)
+          source = "# This migration comes from #{name} (originally #{migration.version})\n#{source}"
 
-            if duplicate = destination_migrations.detect { |m| m.name == migration.name }
-              options[:on_skip].call(name, migration) if File.read(duplicate.filename) != source && options[:on_skip]
-              next
-            end
+          if duplicate = destination_migrations.detect { |m| m.name == migration.name }
+            options[:on_skip].call(name, migration) if File.read(duplicate.filename) != source && options[:on_skip]
+            next
+          end
 
-            migration.version = next_migration_number(last ? last.version + 1 : 0).to_i
-            new_path = File.join(destination, "#{migration.version}_#{migration.name.underscore}.rb")
-            old_path, migration.filename = migration.filename, new_path
-            last = migration
+          migration.version = next_migration_number(last ? last.version + 1 : 0).to_i
+          new_path = File.join(destination, "#{migration.version}_#{migration.name.underscore}.rb")
+          old_path, migration.filename = migration.filename, new_path
+          last = migration
 
-            FileUtils.cp(old_path, migration.filename)
-            copied << migration
-            options[:on_copy].call(name, migration, old_path) if options[:on_copy]
-            destination_migrations << migration
-          end
+          FileUtils.cp(old_path, migration.filename)
+          copied << migration
+          options[:on_copy].call(name, migration, old_path) if options[:on_copy]
+          destination_migrations << migration
         end
-
-        copied
       end
 
-      def next_migration_number(number)
-        if ActiveRecord::Base.timestamped_migrations
-          [Time.now.utc.strftime("%Y%m%d%H%M%S"), "%.14d" % number].max
-        else
-          "%.3d" % number
-        end
+      copied
+    end
+
+    def next_migration_number(number)
+      if ActiveRecord::Base.timestamped_migrations
+        [Time.now.utc.strftime("%Y%m%d%H%M%S"), "%.14d" % number].max
+      else
+        "%.3d" % number
       end
     end
   end
@@ -451,7 +504,7 @@ module ActiveRecord
 
       def load_migration
         require(File.expand_path(filename))
-        name.constantize
+        name.constantize.new
       end
 
   end
diff --git a/activerecord/lib/active_record/migration/command_recorder.rb b/activerecord/lib/active_record/migration/command_recorder.rb
new file mode 100644
index 0000000000..d7e481905a
--- /dev/null
+++ b/activerecord/lib/active_record/migration/command_recorder.rb
@@ -0,0 +1,91 @@
+module ActiveRecord
+  class Migration
+    # ActiveRecord::Migration::CommandRecorder records commands done during
+    # a migration and knows how to reverse those commands.  The CommandRecorder
+    # knows how to invert the following commands:
+    #
+    # * add_column
+    # * add_index
+    # * add_timestamp
+    # * create_table
+    # * remove_timestamps
+    # * rename_column
+    # * rename_index
+    # * rename_table
+    class CommandRecorder
+      attr_accessor :commands, :delegate
+
+      def initialize(delegate = nil)
+        @commands = []
+        @delegate = delegate
+      end
+
+      # record +command+.  +command+ should be a method name and arguments.
+      # For example:
+      #
+      #   recorder.record(:method_name, [:arg1, arg2])
+      def record(*command)
+        @commands << command
+      end
+
+      # Returns a list that represents commands that are the inverse of the
+      # commands stored in +commands+.  For example:
+      #
+      #   recorder.record(:rename_table, [:old, :new])
+      #   recorder.inverse # => [:rename_table, [:new, :old]]
+      #
+      # This method will raise an IrreversibleMigration exception if it cannot
+      # invert the +commands+.
+      def inverse
+        @commands.reverse.map { |name, args|
+          method = :"invert_#{name}"
+          raise IrreversibleMigration unless respond_to?(method, true)
+          __send__(method, args)
+        }
+      end
+
+      def respond_to?(*args) # :nodoc:
+        super || delegate.respond_to?(*args)
+      end
+
+      def send(method, *args) # :nodoc:
+        return super unless respond_to?(method)
+        record(method, args)
+      end
+
+      private
+      def invert_create_table(args)
+        [:drop_table, args]
+      end
+
+      def invert_rename_table(args)
+        [:rename_table, args.reverse]
+      end
+
+      def invert_add_column(args)
+        [:remove_column, args.first(2)]
+      end
+
+      def invert_rename_index(args)
+        [:rename_index, args.reverse]
+      end
+
+      def invert_rename_column(args)
+        [:rename_column, [args.first] + args.last(2).reverse]
+      end
+
+      def invert_add_index(args)
+        table, columns, _ = *args
+        [:remove_index, [table, {:column => columns}]]
+      end
+
+      def invert_remove_timestamps(args)
+        [:add_timestamps, args]
+      end
+
+      def invert_add_timestamps(args)
+        [:remove_timestamps, args]
+      end
+    end
+  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 0c3392263a..050b521b6a 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})"
@@ -413,11 +417,8 @@ 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.
@@ -433,7 +434,7 @@ 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
@@ -442,8 +443,7 @@ 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/reflection.rb b/activerecord/lib/active_record/reflection.rb
index ba37fed3c7..d1de8cefb9 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.
diff --git a/activerecord/lib/active_record/relation/finder_methods.rb b/activerecord/lib/active_record/relation/finder_methods.rb
index 4192456447..23ae0b4325 100644
--- a/activerecord/lib/active_record/relation/finder_methods.rb
+++ b/activerecord/lib/active_record/relation/finder_methods.rb
@@ -202,7 +202,7 @@ module ActiveRecord
     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
 
@@ -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 9c399d3333..0a4c119849 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.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
 
@@ -141,7 +155,7 @@ module ActiveRecord
         "#{@klass.table_name}.#{@klass.primary_key} DESC" :
         reverse_sql_order(order_clause).join(', ')
 
-      except(:order).order(Arel::SqlLiteral.new(order))
+      except(:order).order(Arel.sql(order))
     end
 
     def arel
@@ -174,10 +188,7 @@ module ActiveRecord
 
       arel = build_joins(arel, @joins_values) unless @joins_values.empty?
 
-      (@where_values - ['']).uniq.each do |where|
-        where = Arel.sql(where) if String === where
-        arel = arel.where(Arel::Nodes::Grouping.new(where))
-      end
+      arel = collapse_wheres(arel, (@where_values - ['']).uniq)
 
       arel = arel.having(*@having_values.uniq.reject{|h| h.blank?}) unless @having_values.empty?
 
@@ -198,6 +209,27 @@ module ActiveRecord
 
     private
 
+    def collapse_wheres(arel, wheres)
+      equalities = wheres.grep(Arel::Nodes::Equality)
+
+      groups = equalities.group_by do |equality|
+        equality.left
+      end
+
+      groups.each do |_, eqls|
+        test = eqls.inject(eqls.shift) do |memo, expr|
+          memo.or(expr)
+        end
+        arel = arel.where(test)
+      end
+
+      (wheres - equalities).each do |where|
+        where = Arel.sql(where) if String === where
+        arel = arel.where(Arel::Nodes::Grouping.new(where))
+      end
+      arel
+    end
+
     def build_where(opts, other = [])
       case opts
       when String, Array
diff --git a/activerecord/lib/active_record/schema.rb b/activerecord/lib/active_record/schema.rb
index c1bc3214ea..c6bb5c1961 100644
--- a/activerecord/lib/active_record/schema.rb
+++ b/activerecord/lib/active_record/schema.rb
@@ -30,9 +30,7 @@ module ActiveRecord
   # ActiveRecord::Schema is only supported by database adapters that also
   # support migrations, the two features being very similar.
   class Schema < Migration
-    private_class_method :new
-
-    def self.migrations_path
+    def migrations_path
       ActiveRecord::Migrator.migrations_path
     end
 
@@ -48,11 +46,12 @@ module ActiveRecord
     #     ...
     #   end
     def self.define(info={}, &block)
-      instance_eval(&block)
+      schema = new
+      schema.instance_eval(&block)
 
       unless info[:version].blank?
         initialize_schema_migrations_table
-        assume_migrated_upto_version(info[:version], migrations_path)
+        assume_migrated_upto_version(info[:version], schema.migrations_path)
       end
     end
   end
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/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)