1 files changed, 144 insertions, 0 deletions
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..4121a5b378
--- /dev/null
+++ b/activerecord/lib/active_record/associations/join_dependency/join_association.rb
@@ -0,0 +1,144 @@
+module ActiveRecord
+  module Associations
+    class JoinDependency # :nodoc:
+      class JoinAssociation < JoinPart # :nodoc:
+        include JoinHelper
+
+        # 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
+
+        attr_reader :tables
+
+        delegate :options, :through_reflection, :source_reflection, :chain, :to => :reflection
+        delegate :table, :table_name, :to => :parent, :prefix => :parent
+        delegate :alias_tracker, :to => :join_dependency
+
+        alias :alias_suffix :parent_table_name
+
+        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 }"
+          @tables          = construct_tables.reverse
+        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)
+          tables        = @tables.dup
+          foreign_table = parent_table
+
+          # The chain starts with the target table, but we want to end with it here (makes
+          # more sense in this context), so we reverse
+          chain.reverse.each_with_index do |reflection, i|
+            table = tables.shift
+
+            case reflection.source_macro
+            when :belongs_to
+              key         = reflection.association_primary_key
+              foreign_key = reflection.foreign_key
+            when :has_and_belongs_to_many
+              # Join the join table first...
+              relation.from(join(
+                table,
+                table[reflection.foreign_key].
+                  eq(foreign_table[reflection.active_record_primary_key])
+              ))
+
+              foreign_table, table = table, tables.shift
+
+              key         = reflection.association_primary_key
+              foreign_key = reflection.association_foreign_key
+            else
+              key         = reflection.foreign_key
+              foreign_key = reflection.active_record_primary_key
+            end
+
+            constraint = table[key].eq(foreign_table[foreign_key])
+
+            if reflection.klass.finder_needs_type_condition?
+              constraint = table.create_and([
+                constraint,
+                reflection.klass.send(:type_condition, table)
+              ])
+            end
+
+            relation.from(join(table, constraint))
+
+            unless conditions[i].empty?
+              relation.where(sanitize(conditions[i], table))
+            end
+
+            # The current table in this iteration becomes the foreign table in the next
+            foreign_table = table
+          end
+
+          relation
+        end
+
+        def join_relation(joining_relation)
+          self.join_type = Arel::OuterJoin
+          joining_relation.joins(self)
+        end
+
+        def table
+          tables.last
+        end
+
+        def aliased_table_name
+          table.table_alias || table.name
+        end
+
+        def conditions
+          @conditions ||= reflection.conditions.reverse
+        end
+
+        private
+
+        def interpolate(conditions)
+          if conditions.respond_to?(:to_proc)
+            instance_eval(&conditions)
+          else
+            conditions
+          end
+        end
+
+      end
+    end
+  end
+end