Move JoinDependency and friends from ActiveRecord::Associations::ClassMethods to just ActiveRecord::Associations

11 files changed, 618 insertions, 626 deletions

diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index 0fa9bcd908..e91cbd7f33 100644
--- a/activerecord/lib/active_record/associations.rb
+++ b/activerecord/lib/active_record/associations.rb
@@ -5,7 +5,6 @@ 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:
@@ -143,7 +142,8 @@ module ActiveRecord
       autoload :HasAndBelongsToMany, 'active_record/associations/builder/has_and_belongs_to_many'
     end
 
-    autoload :Preloader, 'active_record/associations/preloader'
+    autoload :Preloader,      'active_record/associations/preloader'
+    autoload :JoinDependency, 'active_record/associations/join_dependency'
 
     # Clears out the association cache.
     def clear_association_cache #:nodoc:
diff --git a/activerecord/lib/active_record/associations/class_methods/join_dependency.rb b/activerecord/lib/active_record/associations/class_methods/join_dependency.rb
deleted file mode 100644
index b711ff35ca..0000000000
--- a/activerecord/lib/active_record/associations/class_methods/join_dependency.rb
+++ /dev/null
@@ -1,233 +0,0 @@
-require 'active_record/associations/class_methods/join_dependency/join_part'
-require 'active_record/associations/class_methods/join_dependency/join_base'
-require 'active_record/associations/class_methods/join_dependency/join_association'
-
-module ActiveRecord
-  module Associations
-    module ClassMethods
-      class JoinDependency # :nodoc:
-        attr_reader :join_parts, :reflections, :table_aliases, :active_record
-
-        def initialize(base, associations, joins)
-          @active_record         = base
-          @table_joins           = joins
-          @join_parts            = [JoinBase.new(base)]
-          @associations          = {}
-          @reflections           = []
-          @table_aliases         = Hash.new do |h,name|
-            h[name] = count_aliases_from_table_joins(name.downcase)
-          end
-          @table_aliases[base.table_name] = 1
-          build(associations)
-        end
-
-        def graft(*associations)
-          associations.each do |association|
-            join_associations.detect {|a| association == a} ||
-              build(association.reflection.name, association.find_parent_in(self) || join_base, association.join_type)
-          end
-          self
-        end
-
-        def join_associations
-          join_parts.last(join_parts.length - 1)
-        end
-
-        def join_base
-          join_parts.first
-        end
-
-        def columns
-          join_parts.collect { |join_part|
-            table = join_part.aliased_table
-            join_part.column_names_with_alias.collect{ |column_name, aliased_name|
-              table[column_name].as Arel.sql(aliased_name)
-            }
-          }.flatten
-        end
-
-        def count_aliases_from_table_joins(name)
-          return 0 if Arel::Table === @table_joins
-
-          # quoted_name should be downcased as some database adapters (Oracle) return quoted name in uppercase
-          quoted_name = active_record.connection.quote_table_name(name).downcase
-
-          @table_joins.map { |join|
-            # Table names + table aliases
-            join.left.downcase.scan(
-              /join(?:\s+\w+)?\s+(\S+\s+)?#{quoted_name}\son/
-            ).size
-          }.sum
-        end
-
-        def instantiate(rows)
-          primary_key = join_base.aliased_primary_key
-          parents = {}
-
-          records = rows.map { |model|
-            primary_id = model[primary_key]
-            parent = parents[primary_id] ||= join_base.instantiate(model)
-            construct(parent, @associations, join_associations, model)
-            parent
-          }.uniq
-
-          remove_duplicate_results!(active_record, records, @associations)
-          records
-        end
-
-        def remove_duplicate_results!(base, records, associations)
-          case associations
-          when Symbol, String
-            reflection = base.reflections[associations]
-            remove_uniq_by_reflection(reflection, records)
-          when Array
-            associations.each do |association|
-              remove_duplicate_results!(base, records, association)
-            end
-          when Hash
-            associations.keys.each do |name|
-              reflection = base.reflections[name]
-              remove_uniq_by_reflection(reflection, records)
-
-              parent_records = []
-              records.each do |record|
-                if descendant = record.send(reflection.name)
-                  if reflection.collection?
-                    parent_records.concat descendant.target.uniq
-                  else
-                    parent_records << descendant
-                  end
-                end
-              end
-
-              remove_duplicate_results!(reflection.klass, parent_records, associations[name]) unless parent_records.empty?
-            end
-          end
-        end
-
-        protected
-
-        def cache_joined_association(association)
-          associations = []
-          parent = association.parent
-          while parent != join_base
-            associations.unshift(parent.reflection.name)
-            parent = parent.parent
-          end
-          ref = @associations
-          associations.each do |key|
-            ref = ref[key]
-          end
-          ref[association.reflection.name] ||= {}
-        end
-
-        def build(associations, parent = nil, join_type = Arel::InnerJoin)
-          parent ||= join_parts.last
-          case associations
-          when Symbol, String
-            reflection = parent.reflections[associations.to_s.intern] or
-            raise ConfigurationError, "Association named '#{ associations }' was not found; perhaps you misspelled it?"
-            unless join_association = find_join_association(reflection, parent)
-              @reflections << reflection
-              join_association = build_join_association(reflection, parent)
-              join_association.join_type = join_type
-              @join_parts << join_association
-              cache_joined_association(join_association)
-            end
-            join_association
-          when Array
-            associations.each do |association|
-              build(association, parent, join_type)
-            end
-          when Hash
-            associations.keys.sort_by { |a| a.to_s }.each do |name|
-              join_association = build(name, parent, join_type)
-              build(associations[name], join_association, join_type)
-            end
-          else
-            raise ConfigurationError, associations.inspect
-          end
-        end
-
-        def find_join_association(name_or_reflection, parent)
-          if String === name_or_reflection
-            name_or_reflection = name_or_reflection.to_sym
-          end
-
-          join_associations.detect { |j|
-            j.reflection == name_or_reflection && j.parent == parent
-          }
-        end
-
-        def remove_uniq_by_reflection(reflection, records)
-          if reflection && reflection.collection?
-            records.each { |record| record.send(reflection.name).target.uniq! }
-          end
-        end
-
-        def build_join_association(reflection, parent)
-          JoinAssociation.new(reflection, self, parent)
-        end
-
-        def construct(parent, associations, join_parts, row)
-          case associations
-          when Symbol, String
-            name = associations.to_s
-
-            join_part = join_parts.detect { |j|
-              j.reflection.name.to_s == name &&
-                j.parent_table_name == parent.class.table_name }
-
-              raise(ConfigurationError, "No such association") unless join_part
-
-              join_parts.delete(join_part)
-              construct_association(parent, join_part, row)
-          when Array
-            associations.each do |association|
-              construct(parent, association, join_parts, row)
-            end
-          when Hash
-            associations.sort_by { |k,_| k.to_s }.each do |association_name, assoc|
-              association = construct(parent, association_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.association_cache.key?(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
-              other = record.association(join_part.reflection.name)
-              other.loaded!
-              other.target.push(association)
-              other.set_inverse_instance(association)
-            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)
-          other = record.association(join_part.reflection.name)
-          other.target = association
-          other.set_inverse_instance(association)
-        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
deleted file mode 100644
index aaa475109e..0000000000
--- a/activerecord/lib/active_record/associations/class_methods/join_dependency/join_association.rb
+++ /dev/null
@@ -1,281 +0,0 @@
-module ActiveRecord
-  module Associations
-    module ClassMethods
-      class JoinDependency # :nodoc:
-        class JoinAssociation < JoinPart # :nodoc:
-          # The reflection of the association represented
-          attr_reader :reflection
-
-          # The JoinDependency object which this JoinAssociation exists within. This is mainly
-          # relevant for generating aliases which do not conflict with other joins which are
-          # part of the query.
-          attr_reader :join_dependency
-
-          # A JoinBase instance representing the active record we are joining onto.
-          # (So in Author.has_many :posts, the Author would be that base record.)
-          attr_reader :parent
-
-          # What type of join will be generated, either Arel::InnerJoin (default) or Arel::OuterJoin
-          attr_accessor :join_type
-
-          # These implement abstract methods from the superclass
-          attr_reader :aliased_prefix, :aliased_table_name
-
-          delegate :options, :through_reflection, :source_reflection, :to => :reflection
-          delegate :table, :table_name, :to => :parent, :prefix => :parent
-
-          def initialize(reflection, join_dependency, parent = nil)
-            reflection.check_validity!
-
-            if reflection.options[:polymorphic]
-              raise EagerLoadPolymorphicError.new(reflection)
-            end
-
-            super(reflection.klass)
-
-            @reflection      = reflection
-            @join_dependency = join_dependency
-            @parent          = parent
-            @join_type       = Arel::InnerJoin
-            @aliased_prefix  = "t#{ join_dependency.join_parts.size }"
-
-            # This must be done eagerly upon initialisation because the alias which is produced
-            # depends on the state of the join dependency, but we want it to work the same way
-            # every time.
-            allocate_aliases
-            @table = Arel::Table.new(
-              table_name, :as => aliased_table_name, :engine => arel_engine
-            )
-          end
-
-          def ==(other)
-            other.class == self.class &&
-              other.reflection == reflection &&
-              other.parent == parent
-          end
-
-          def find_parent_in(other_join_dependency)
-            other_join_dependency.join_parts.detect do |join_part|
-              parent == join_part
-            end
-          end
-
-          def join_to(relation)
-            send("join_#{reflection.macro}_to", relation)
-          end
-
-          def join_relation(joining_relation)
-            self.join_type = Arel::OuterJoin
-            joining_relation.joins(self)
-          end
-
-          attr_reader :table
-          # More semantic name given we are talking about associations
-          alias_method :target_table, :table
-
-          protected
-
-          def aliased_table_name_for(name, suffix = nil)
-            aliases = @join_dependency.table_aliases
-
-            if aliases[name] != 0 # We need an alias
-              connection = active_record.connection
-
-              name = connection.table_alias_for "#{pluralize(reflection.name)}_#{parent_table_name}#{suffix}"
-              aliases[name] += 1
-              name = name[0, connection.table_alias_length-3] + "_#{aliases[name]}" if aliases[name] > 1
-            else
-              aliases[name] += 1
-            end
-
-            name
-          end
-
-          def pluralize(table_name)
-            ActiveRecord::Base.pluralize_table_names ? table_name.to_s.pluralize : table_name
-          end
-
-          private
-
-          def allocate_aliases
-            @aliased_table_name = aliased_table_name_for(table_name)
-
-            if reflection.macro == :has_and_belongs_to_many
-              @aliased_join_table_name = aliased_table_name_for(reflection.options[:join_table], "_join")
-            elsif [:has_many, :has_one].include?(reflection.macro) && reflection.options[:through]
-              @aliased_join_table_name = aliased_table_name_for(reflection.through_reflection.klass.table_name, "_join")
-            end
-          end
-
-          def process_conditions(conditions, table_name)
-            if conditions.respond_to?(:to_proc)
-              conditions = instance_eval(&conditions)
-            end
-
-            Arel.sql(sanitize_sql(conditions, table_name))
-          end
-
-          def sanitize_sql(condition, table_name)
-            active_record.send(:sanitize_sql, condition, table_name)
-          end
-
-          def join_target_table(relation, condition)
-            conditions = [condition]
-
-            # If the target table is an STI model then we must be sure to only include records of
-            # its type and its sub-types.
-            unless active_record.descends_from_active_record?
-              sti_column    = target_table[active_record.inheritance_column]
-              subclasses    = active_record.descendants
-              sti_condition = sti_column.eq(active_record.sti_name)
-
-              conditions << subclasses.inject(sti_condition) { |attr,subclass|
-                attr.or(sti_column.eq(subclass.sti_name))
-              }
-            end
-
-            # If the reflection has conditions, add them
-            if options[:conditions]
-              conditions << process_conditions(options[:conditions], aliased_table_name)
-            end
-
-            ands = relation.create_and(conditions)
-
-            join = relation.create_join(
-              target_table,
-              relation.create_on(ands),
-              join_type)
-
-            relation.from join
-          end
-
-          def join_has_and_belongs_to_many_to(relation)
-            join_table = Arel::Table.new(
-              options[:join_table]
-            ).alias(@aliased_join_table_name)
-
-            fk       = options[:foreign_key]             || reflection.active_record.to_s.foreign_key
-            klass_fk = options[:association_foreign_key] || reflection.klass.to_s.foreign_key
-
-            relation = relation.join(join_table, join_type)
-            relation = relation.on(
-              join_table[fk].
-              eq(parent_table[reflection.active_record.primary_key])
-            )
-
-            join_target_table(
-              relation,
-              target_table[reflection.klass.primary_key].
-              eq(join_table[klass_fk])
-            )
-          end
-
-          def join_has_many_to(relation)
-            if reflection.options[:through]
-              join_has_many_through_to(relation)
-            elsif reflection.options[:as]
-              join_has_many_polymorphic_to(relation)
-            else
-              foreign_key = options[:foreign_key] || reflection.active_record.name.foreign_key
-              primary_key = options[:primary_key] || parent.primary_key
-
-              join_target_table(
-                relation,
-                target_table[foreign_key].
-                eq(parent_table[primary_key])
-              )
-            end
-          end
-          alias :join_has_one_to :join_has_many_to
-
-          def join_has_many_through_to(relation)
-            join_table = Arel::Table.new(
-              through_reflection.klass.table_name
-            ).alias @aliased_join_table_name
-
-            jt_conditions = []
-            first_key = second_key = nil
-
-            if through_reflection.macro == :belongs_to
-              jt_primary_key = through_reflection.foreign_key
-              jt_foreign_key = through_reflection.association_primary_key
-            else
-              jt_primary_key = through_reflection.active_record_primary_key
-              jt_foreign_key = through_reflection.foreign_key
-
-              if through_reflection.options[:as] # has_many :through against a polymorphic join
-                jt_conditions <<
-                join_table["#{through_reflection.options[:as]}_type"].
-                  eq(parent.active_record.base_class.name)
-              end
-            end
-
-            case source_reflection.macro
-            when :has_many
-              second_key = options[:foreign_key] || primary_key
-
-              if source_reflection.options[:as]
-                first_key = "#{source_reflection.options[:as]}_id"
-              else
-                first_key = through_reflection.klass.base_class.to_s.foreign_key
-              end
-
-              unless through_reflection.klass.descends_from_active_record?
-                jt_conditions <<
-                join_table[through_reflection.active_record.inheritance_column].
-                  eq(through_reflection.klass.sti_name)
-              end
-            when :belongs_to
-              first_key = primary_key
-
-              if reflection.options[:source_type]
-                second_key = source_reflection.association_foreign_key
-
-                jt_conditions <<
-                join_table[reflection.source_reflection.foreign_type].
-                  eq(reflection.options[:source_type])
-              else
-                second_key = source_reflection.foreign_key
-              end
-            end
-
-            jt_conditions <<
-            parent_table[jt_primary_key].
-              eq(join_table[jt_foreign_key])
-
-            if through_reflection.options[:conditions]
-              jt_conditions << process_conditions(through_reflection.options[:conditions], aliased_table_name)
-            end
-
-            relation = relation.join(join_table, join_type).on(*jt_conditions)
-
-            join_target_table(
-              relation,
-              target_table[first_key].eq(join_table[second_key])
-            )
-          end
-
-          def join_has_many_polymorphic_to(relation)
-            join_target_table(
-              relation,
-              target_table["#{reflection.options[:as]}_id"].
-              eq(parent_table[parent.primary_key]).and(
-              target_table["#{reflection.options[:as]}_type"].
-              eq(parent.active_record.base_class.name))
-            )
-          end
-
-          def join_belongs_to_to(relation)
-            foreign_key = options[:foreign_key] || reflection.foreign_key
-            primary_key = options[:primary_key] || reflection.klass.primary_key
-
-            join_target_table(
-              relation,
-              target_table[primary_key].eq(parent_table[foreign_key])
-            )
-          end
-        end
-      end
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/associations/class_methods/join_dependency/join_base.rb b/activerecord/lib/active_record/associations/class_methods/join_dependency/join_base.rb
deleted file mode 100644
index 67567f06df..0000000000
--- a/activerecord/lib/active_record/associations/class_methods/join_dependency/join_base.rb
+++ /dev/null
@@ -1,26 +0,0 @@
-module ActiveRecord
-  module Associations
-    module ClassMethods
-      class JoinDependency # :nodoc:
-        class JoinBase < JoinPart # :nodoc:
-          def ==(other)
-            other.class == self.class &&
-              other.active_record == active_record
-          end
-
-          def aliased_prefix
-            "t0"
-          end
-
-          def table
-            Arel::Table.new(table_name, arel_engine)
-          end
-
-          def aliased_table_name
-            active_record.table_name
-          end
-        end
-      end
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/associations/class_methods/join_dependency/join_part.rb b/activerecord/lib/active_record/associations/class_methods/join_dependency/join_part.rb
deleted file mode 100644
index cd16ae5a8b..0000000000
--- a/activerecord/lib/active_record/associations/class_methods/join_dependency/join_part.rb
+++ /dev/null
@@ -1,80 +0,0 @@
-module ActiveRecord
-  module Associations
-    module ClassMethods
-      class JoinDependency # :nodoc:
-        # A JoinPart represents a part of a JoinDependency. It is an abstract class, inherited
-        # by JoinBase and JoinAssociation. A JoinBase represents the Active Record which
-        # everything else is being joined onto. A JoinAssociation represents an association which
-        # is joining to the base. A JoinAssociation may result in more than one actual join
-        # operations (for example a has_and_belongs_to_many JoinAssociation would result in
-        # two; one for the join table and one for the target table).
-        class JoinPart # :nodoc:
-          # The Active Record class which this join part is associated 'about'; for a JoinBase
-          # this is the actual base model, for a JoinAssociation this is the target model of the
-          # association.
-          attr_reader :active_record
-
-          delegate :table_name, :column_names, :primary_key, :reflections, :arel_engine, :to => :active_record
-
-          def initialize(active_record)
-            @active_record = active_record
-            @cached_record = {}
-            @column_names_with_alias = nil
-          end
-
-          def aliased_table
-            Arel::Nodes::TableAlias.new aliased_table_name, table
-          end
-
-          def ==(other)
-            raise NotImplementedError
-          end
-
-          # An Arel::Table for the active_record
-          def table
-            raise NotImplementedError
-          end
-
-          # The prefix to be used when aliasing columns in the active_record's table
-          def aliased_prefix
-            raise NotImplementedError
-          end
-
-          # The alias for the active_record's table
-          def aliased_table_name
-            raise NotImplementedError
-          end
-
-          # The alias for the primary key of the active_record's table
-          def aliased_primary_key
-            "#{aliased_prefix}_r0"
-          end
-
-          # An array of [column_name, alias] pairs for the table
-          def column_names_with_alias
-            unless @column_names_with_alias
-              @column_names_with_alias = []
-
-              ([primary_key] + (column_names - [primary_key])).each_with_index do |column_name, i|
-                @column_names_with_alias << [column_name, "#{aliased_prefix}_r#{i}"]
-              end
-            end
-            @column_names_with_alias
-          end
-
-          def extract_record(row)
-            Hash[column_names_with_alias.map{|cn, an| [cn, row[an]]}]
-          end
-
-          def record_id(row)
-            row[aliased_primary_key]
-          end
-
-          def instantiate(row)
-            @cached_record[record_id(row)] ||= active_record.send(:instantiate, extract_record(row))
-          end
-        end
-      end
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/associations/join_dependency.rb b/activerecord/lib/active_record/associations/join_dependency.rb
new file mode 100644
index 0000000000..c7c3cf521c
--- /dev/null
+++ b/activerecord/lib/active_record/associations/join_dependency.rb
@@ -0,0 +1,231 @@
+module ActiveRecord
+  module Associations
+    class JoinDependency # :nodoc:
+      autoload :JoinPart,        'active_record/associations/join_dependency/join_part'
+      autoload :JoinBase,        'active_record/associations/join_dependency/join_base'
+      autoload :JoinAssociation, 'active_record/associations/join_dependency/join_association'
+
+      attr_reader :join_parts, :reflections, :table_aliases, :active_record
+
+      def initialize(base, associations, joins)
+        @active_record         = base
+        @table_joins           = joins
+        @join_parts            = [JoinBase.new(base)]
+        @associations          = {}
+        @reflections           = []
+        @table_aliases         = Hash.new do |h,name|
+          h[name] = count_aliases_from_table_joins(name.downcase)
+        end
+        @table_aliases[base.table_name] = 1
+        build(associations)
+      end
+
+      def graft(*associations)
+        associations.each do |association|
+          join_associations.detect {|a| association == a} ||
+            build(association.reflection.name, association.find_parent_in(self) || join_base, association.join_type)
+        end
+        self
+      end
+
+      def join_associations
+        join_parts.last(join_parts.length - 1)
+      end
+
+      def join_base
+        join_parts.first
+      end
+
+      def columns
+        join_parts.collect { |join_part|
+          table = join_part.aliased_table
+          join_part.column_names_with_alias.collect{ |column_name, aliased_name|
+            table[column_name].as Arel.sql(aliased_name)
+          }
+        }.flatten
+      end
+
+      def count_aliases_from_table_joins(name)
+        return 0 if Arel::Table === @table_joins
+
+        # quoted_name should be downcased as some database adapters (Oracle) return quoted name in uppercase
+        quoted_name = active_record.connection.quote_table_name(name).downcase
+
+        @table_joins.map { |join|
+          # Table names + table aliases
+          join.left.downcase.scan(
+            /join(?:\s+\w+)?\s+(\S+\s+)?#{quoted_name}\son/
+          ).size
+        }.sum
+      end
+
+      def instantiate(rows)
+        primary_key = join_base.aliased_primary_key
+        parents = {}
+
+        records = rows.map { |model|
+          primary_id = model[primary_key]
+          parent = parents[primary_id] ||= join_base.instantiate(model)
+          construct(parent, @associations, join_associations, model)
+          parent
+        }.uniq
+
+        remove_duplicate_results!(active_record, records, @associations)
+        records
+      end
+
+      def remove_duplicate_results!(base, records, associations)
+        case associations
+        when Symbol, String
+          reflection = base.reflections[associations]
+          remove_uniq_by_reflection(reflection, records)
+        when Array
+          associations.each do |association|
+            remove_duplicate_results!(base, records, association)
+          end
+        when Hash
+          associations.keys.each do |name|
+            reflection = base.reflections[name]
+            remove_uniq_by_reflection(reflection, records)
+
+            parent_records = []
+            records.each do |record|
+              if descendant = record.send(reflection.name)
+                if reflection.collection?
+                  parent_records.concat descendant.target.uniq
+                else
+                  parent_records << descendant
+                end
+              end
+            end
+
+            remove_duplicate_results!(reflection.klass, parent_records, associations[name]) unless parent_records.empty?
+          end
+        end
+      end
+
+      protected
+
+      def cache_joined_association(association)
+        associations = []
+        parent = association.parent
+        while parent != join_base
+          associations.unshift(parent.reflection.name)
+          parent = parent.parent
+        end
+        ref = @associations
+        associations.each do |key|
+          ref = ref[key]
+        end
+        ref[association.reflection.name] ||= {}
+      end
+
+      def build(associations, parent = nil, join_type = Arel::InnerJoin)
+        parent ||= join_parts.last
+        case associations
+        when Symbol, String
+          reflection = parent.reflections[associations.to_s.intern] or
+          raise ConfigurationError, "Association named '#{ associations }' was not found; perhaps you misspelled it?"
+          unless join_association = find_join_association(reflection, parent)
+            @reflections << reflection
+            join_association = build_join_association(reflection, parent)
+            join_association.join_type = join_type
+            @join_parts << join_association
+            cache_joined_association(join_association)
+          end
+          join_association
+        when Array
+          associations.each do |association|
+            build(association, parent, join_type)
+          end
+        when Hash
+          associations.keys.sort_by { |a| a.to_s }.each do |name|
+            join_association = build(name, parent, join_type)
+            build(associations[name], join_association, join_type)
+          end
+        else
+          raise ConfigurationError, associations.inspect
+        end
+      end
+
+      def find_join_association(name_or_reflection, parent)
+        if String === name_or_reflection
+          name_or_reflection = name_or_reflection.to_sym
+        end
+
+        join_associations.detect { |j|
+          j.reflection == name_or_reflection && j.parent == parent
+        }
+      end
+
+      def remove_uniq_by_reflection(reflection, records)
+        if reflection && reflection.collection?
+          records.each { |record| record.send(reflection.name).target.uniq! }
+        end
+      end
+
+      def build_join_association(reflection, parent)
+        JoinAssociation.new(reflection, self, parent)
+      end
+
+      def construct(parent, associations, join_parts, row)
+        case associations
+        when Symbol, String
+          name = associations.to_s
+
+          join_part = join_parts.detect { |j|
+            j.reflection.name.to_s == name &&
+              j.parent_table_name == parent.class.table_name }
+
+            raise(ConfigurationError, "No such association") unless join_part
+
+            join_parts.delete(join_part)
+            construct_association(parent, join_part, row)
+        when Array
+          associations.each do |association|
+            construct(parent, association, join_parts, row)
+          end
+        when Hash
+          associations.sort_by { |k,_| k.to_s }.each do |association_name, assoc|
+            association = construct(parent, association_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.association_cache.key?(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
+            other = record.association(join_part.reflection.name)
+            other.loaded!
+            other.target.push(association)
+            other.set_inverse_instance(association)
+          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)
+        other = record.association(join_part.reflection.name)
+        other.target = association
+        other.set_inverse_instance(association)
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/associations/join_dependency/join_association.rb b/activerecord/lib/active_record/associations/join_dependency/join_association.rb
new file mode 100644
index 0000000000..ebe39c35fe
--- /dev/null
+++ b/activerecord/lib/active_record/associations/join_dependency/join_association.rb
@@ -0,0 +1,279 @@
+module ActiveRecord
+  module Associations
+    class JoinDependency # :nodoc:
+      class JoinAssociation < JoinPart # :nodoc:
+        # The reflection of the association represented
+        attr_reader :reflection
+
+        # The JoinDependency object which this JoinAssociation exists within. This is mainly
+        # relevant for generating aliases which do not conflict with other joins which are
+        # part of the query.
+        attr_reader :join_dependency
+
+        # A JoinBase instance representing the active record we are joining onto.
+        # (So in Author.has_many :posts, the Author would be that base record.)
+        attr_reader :parent
+
+        # What type of join will be generated, either Arel::InnerJoin (default) or Arel::OuterJoin
+        attr_accessor :join_type
+
+        # These implement abstract methods from the superclass
+        attr_reader :aliased_prefix, :aliased_table_name
+
+        delegate :options, :through_reflection, :source_reflection, :to => :reflection
+        delegate :table, :table_name, :to => :parent, :prefix => :parent
+
+        def initialize(reflection, join_dependency, parent = nil)
+          reflection.check_validity!
+
+          if reflection.options[:polymorphic]
+            raise EagerLoadPolymorphicError.new(reflection)
+          end
+
+          super(reflection.klass)
+
+          @reflection      = reflection
+          @join_dependency = join_dependency
+          @parent          = parent
+          @join_type       = Arel::InnerJoin
+          @aliased_prefix  = "t#{ join_dependency.join_parts.size }"
+
+          # This must be done eagerly upon initialisation because the alias which is produced
+          # depends on the state of the join dependency, but we want it to work the same way
+          # every time.
+          allocate_aliases
+          @table = Arel::Table.new(
+            table_name, :as => aliased_table_name, :engine => arel_engine
+          )
+        end
+
+        def ==(other)
+          other.class == self.class &&
+            other.reflection == reflection &&
+            other.parent == parent
+        end
+
+        def find_parent_in(other_join_dependency)
+          other_join_dependency.join_parts.detect do |join_part|
+            parent == join_part
+          end
+        end
+
+        def join_to(relation)
+          send("join_#{reflection.macro}_to", relation)
+        end
+
+        def join_relation(joining_relation)
+          self.join_type = Arel::OuterJoin
+          joining_relation.joins(self)
+        end
+
+        attr_reader :table
+        # More semantic name given we are talking about associations
+        alias_method :target_table, :table
+
+        protected
+
+        def aliased_table_name_for(name, suffix = nil)
+          aliases = @join_dependency.table_aliases
+
+          if aliases[name] != 0 # We need an alias
+            connection = active_record.connection
+
+            name = connection.table_alias_for "#{pluralize(reflection.name)}_#{parent_table_name}#{suffix}"
+            aliases[name] += 1
+            name = name[0, connection.table_alias_length-3] + "_#{aliases[name]}" if aliases[name] > 1
+          else
+            aliases[name] += 1
+          end
+
+          name
+        end
+
+        def pluralize(table_name)
+          ActiveRecord::Base.pluralize_table_names ? table_name.to_s.pluralize : table_name
+        end
+
+        private
+
+        def allocate_aliases
+          @aliased_table_name = aliased_table_name_for(table_name)
+
+          if reflection.macro == :has_and_belongs_to_many
+            @aliased_join_table_name = aliased_table_name_for(reflection.options[:join_table], "_join")
+          elsif [:has_many, :has_one].include?(reflection.macro) && reflection.options[:through]
+            @aliased_join_table_name = aliased_table_name_for(reflection.through_reflection.klass.table_name, "_join")
+          end
+        end
+
+        def process_conditions(conditions, table_name)
+          if conditions.respond_to?(:to_proc)
+            conditions = instance_eval(&conditions)
+          end
+
+          Arel.sql(sanitize_sql(conditions, table_name))
+        end
+
+        def sanitize_sql(condition, table_name)
+          active_record.send(:sanitize_sql, condition, table_name)
+        end
+
+        def join_target_table(relation, condition)
+          conditions = [condition]
+
+          # If the target table is an STI model then we must be sure to only include records of
+          # its type and its sub-types.
+          unless active_record.descends_from_active_record?
+            sti_column    = target_table[active_record.inheritance_column]
+            subclasses    = active_record.descendants
+            sti_condition = sti_column.eq(active_record.sti_name)
+
+            conditions << subclasses.inject(sti_condition) { |attr,subclass|
+              attr.or(sti_column.eq(subclass.sti_name))
+            }
+          end
+
+          # If the reflection has conditions, add them
+          if options[:conditions]
+            conditions << process_conditions(options[:conditions], aliased_table_name)
+          end
+
+          ands = relation.create_and(conditions)
+
+          join = relation.create_join(
+            target_table,
+            relation.create_on(ands),
+            join_type)
+
+          relation.from join
+        end
+
+        def join_has_and_belongs_to_many_to(relation)
+          join_table = Arel::Table.new(
+            options[:join_table]
+          ).alias(@aliased_join_table_name)
+
+          fk       = options[:foreign_key]             || reflection.active_record.to_s.foreign_key
+          klass_fk = options[:association_foreign_key] || reflection.klass.to_s.foreign_key
+
+          relation = relation.join(join_table, join_type)
+          relation = relation.on(
+            join_table[fk].
+            eq(parent_table[reflection.active_record.primary_key])
+          )
+
+          join_target_table(
+            relation,
+            target_table[reflection.klass.primary_key].
+            eq(join_table[klass_fk])
+          )
+        end
+
+        def join_has_many_to(relation)
+          if reflection.options[:through]
+            join_has_many_through_to(relation)
+          elsif reflection.options[:as]
+            join_has_many_polymorphic_to(relation)
+          else
+            foreign_key = options[:foreign_key] || reflection.active_record.name.foreign_key
+            primary_key = options[:primary_key] || parent.primary_key
+
+            join_target_table(
+              relation,
+              target_table[foreign_key].
+              eq(parent_table[primary_key])
+            )
+          end
+        end
+        alias :join_has_one_to :join_has_many_to
+
+        def join_has_many_through_to(relation)
+          join_table = Arel::Table.new(
+            through_reflection.klass.table_name
+          ).alias @aliased_join_table_name
+
+          jt_conditions = []
+          first_key = second_key = nil
+
+          if through_reflection.macro == :belongs_to
+            jt_primary_key = through_reflection.foreign_key
+            jt_foreign_key = through_reflection.association_primary_key
+          else
+            jt_primary_key = through_reflection.active_record_primary_key
+            jt_foreign_key = through_reflection.foreign_key
+
+            if through_reflection.options[:as] # has_many :through against a polymorphic join
+              jt_conditions <<
+              join_table["#{through_reflection.options[:as]}_type"].
+                eq(parent.active_record.base_class.name)
+            end
+          end
+
+          case source_reflection.macro
+          when :has_many
+            second_key = options[:foreign_key] || primary_key
+
+            if source_reflection.options[:as]
+              first_key = "#{source_reflection.options[:as]}_id"
+            else
+              first_key = through_reflection.klass.base_class.to_s.foreign_key
+            end
+
+            unless through_reflection.klass.descends_from_active_record?
+              jt_conditions <<
+              join_table[through_reflection.active_record.inheritance_column].
+                eq(through_reflection.klass.sti_name)
+            end
+          when :belongs_to
+            first_key = primary_key
+
+            if reflection.options[:source_type]
+              second_key = source_reflection.association_foreign_key
+
+              jt_conditions <<
+              join_table[reflection.source_reflection.foreign_type].
+                eq(reflection.options[:source_type])
+            else
+              second_key = source_reflection.foreign_key
+            end
+          end
+
+          jt_conditions <<
+          parent_table[jt_primary_key].
+            eq(join_table[jt_foreign_key])
+
+          if through_reflection.options[:conditions]
+            jt_conditions << process_conditions(through_reflection.options[:conditions], aliased_table_name)
+          end
+
+          relation = relation.join(join_table, join_type).on(*jt_conditions)
+
+          join_target_table(
+            relation,
+            target_table[first_key].eq(join_table[second_key])
+          )
+        end
+
+        def join_has_many_polymorphic_to(relation)
+          join_target_table(
+            relation,
+            target_table["#{reflection.options[:as]}_id"].
+            eq(parent_table[parent.primary_key]).and(
+            target_table["#{reflection.options[:as]}_type"].
+            eq(parent.active_record.base_class.name))
+          )
+        end
+
+        def join_belongs_to_to(relation)
+          foreign_key = options[:foreign_key] || reflection.foreign_key
+          primary_key = options[:primary_key] || reflection.klass.primary_key
+
+          join_target_table(
+            relation,
+            target_table[primary_key].eq(parent_table[foreign_key])
+          )
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/associations/join_dependency/join_base.rb b/activerecord/lib/active_record/associations/join_dependency/join_base.rb
new file mode 100644
index 0000000000..3920e84976
--- /dev/null
+++ b/activerecord/lib/active_record/associations/join_dependency/join_base.rb
@@ -0,0 +1,24 @@
+module ActiveRecord
+  module Associations
+    class JoinDependency # :nodoc:
+      class JoinBase < JoinPart # :nodoc:
+        def ==(other)
+          other.class == self.class &&
+            other.active_record == active_record
+        end
+
+        def aliased_prefix
+          "t0"
+        end
+
+        def table
+          Arel::Table.new(table_name, arel_engine)
+        end
+
+        def aliased_table_name
+          active_record.table_name
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/associations/join_dependency/join_part.rb b/activerecord/lib/active_record/associations/join_dependency/join_part.rb
new file mode 100644
index 0000000000..3279e56e7d
--- /dev/null
+++ b/activerecord/lib/active_record/associations/join_dependency/join_part.rb
@@ -0,0 +1,78 @@
+module ActiveRecord
+  module Associations
+    class JoinDependency # :nodoc:
+      # A JoinPart represents a part of a JoinDependency. It is an abstract class, inherited
+      # by JoinBase and JoinAssociation. A JoinBase represents the Active Record which
+      # everything else is being joined onto. A JoinAssociation represents an association which
+      # is joining to the base. A JoinAssociation may result in more than one actual join
+      # operations (for example a has_and_belongs_to_many JoinAssociation would result in
+      # two; one for the join table and one for the target table).
+      class JoinPart # :nodoc:
+        # The Active Record class which this join part is associated 'about'; for a JoinBase
+        # this is the actual base model, for a JoinAssociation this is the target model of the
+        # association.
+        attr_reader :active_record
+
+        delegate :table_name, :column_names, :primary_key, :reflections, :arel_engine, :to => :active_record
+
+        def initialize(active_record)
+          @active_record = active_record
+          @cached_record = {}
+          @column_names_with_alias = nil
+        end
+
+        def aliased_table
+          Arel::Nodes::TableAlias.new aliased_table_name, table
+        end
+
+        def ==(other)
+          raise NotImplementedError
+        end
+
+        # An Arel::Table for the active_record
+        def table
+          raise NotImplementedError
+        end
+
+        # The prefix to be used when aliasing columns in the active_record's table
+        def aliased_prefix
+          raise NotImplementedError
+        end
+
+        # The alias for the active_record's table
+        def aliased_table_name
+          raise NotImplementedError
+        end
+
+        # The alias for the primary key of the active_record's table
+        def aliased_primary_key
+          "#{aliased_prefix}_r0"
+        end
+
+        # An array of [column_name, alias] pairs for the table
+        def column_names_with_alias
+          unless @column_names_with_alias
+            @column_names_with_alias = []
+
+            ([primary_key] + (column_names - [primary_key])).each_with_index do |column_name, i|
+              @column_names_with_alias << [column_name, "#{aliased_prefix}_r#{i}"]
+            end
+          end
+          @column_names_with_alias
+        end
+
+        def extract_record(row)
+          Hash[column_names_with_alias.map{|cn, an| [cn, row[an]]}]
+        end
+
+        def record_id(row)
+          row[aliased_primary_key]
+        end
+
+        def instantiate(row)
+          @cached_record[record_id(row)] ||= active_record.send(:instantiate, extract_record(row))
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/relation/finder_methods.rb b/activerecord/lib/active_record/relation/finder_methods.rb
index 7f32e5538e..426000fde1 100644
--- a/activerecord/lib/active_record/relation/finder_methods.rb
+++ b/activerecord/lib/active_record/relation/finder_methods.rb
@@ -187,7 +187,7 @@ module ActiveRecord
 
     def find_with_associations
       including = (@eager_load_values + @includes_values).uniq
-      join_dependency = ActiveRecord::Associations::ClassMethods::JoinDependency.new(@klass, including, [])
+      join_dependency = ActiveRecord::Associations::JoinDependency.new(@klass, including, [])
       relation = construct_relation_for_association_find(join_dependency)
       rows = connection.select_all(relation.to_sql, 'SQL', relation.bind_values)
       join_dependency.instantiate(rows)
@@ -197,7 +197,7 @@ module ActiveRecord
 
     def construct_relation_for_association_calculations
       including = (@eager_load_values + @includes_values).uniq
-      join_dependency = ActiveRecord::Associations::ClassMethods::JoinDependency.new(@klass, including, arel.froms.first)
+      join_dependency = ActiveRecord::Associations::JoinDependency.new(@klass, including, arel.froms.first)
       relation = except(:includes, :eager_load, :preload)
       apply_join_dependency(relation, join_dependency)
     end
diff --git a/activerecord/lib/active_record/relation/query_methods.rb b/activerecord/lib/active_record/relation/query_methods.rb
index 4330d850fe..cd1d7108b3 100644
--- a/activerecord/lib/active_record/relation/query_methods.rb
+++ b/activerecord/lib/active_record/relation/query_methods.rb
@@ -236,7 +236,7 @@ module ActiveRecord
           'string_join'
         when Hash, Symbol, Array
           'association_join'
-        when ActiveRecord::Associations::ClassMethods::JoinDependency::JoinAssociation
+        when ActiveRecord::Associations::JoinDependency::JoinAssociation
           'stashed_join'
         when Arel::Nodes::Join
           'join_node'
@@ -254,7 +254,7 @@ module ActiveRecord
 
       join_list = custom_join_ast(manager, string_joins)
 
-      join_dependency = ActiveRecord::Associations::ClassMethods::JoinDependency.new(
+      join_dependency = ActiveRecord::Associations::JoinDependency.new(
         @klass,
         association_joins,
         join_list