1 files changed, 67 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/associations/preloader/through_association.rb b/activerecord/lib/active_record/associations/preloader/through_association.rb
new file mode 100644
index 0000000000..ad6374d09a
--- /dev/null
+++ b/activerecord/lib/active_record/associations/preloader/through_association.rb
@@ -0,0 +1,67 @@
+module ActiveRecord
+  module Associations
+    class Preloader
+      module ThroughAssociation #:nodoc:
+
+        def through_reflection
+          reflection.through_reflection
+        end
+
+        def source_reflection
+          reflection.source_reflection
+        end
+
+        def associated_records_by_owner
+          through_records = through_records_by_owner
+
+          ActiveRecord::Associations::Preloader.new(
+            through_records.values.flatten,
+            source_reflection.name, options
+          ).run
+
+          through_records.each do |owner, records|
+            records.map! { |r| r.send(source_reflection.name) }.flatten!
+            records.compact!
+          end
+        end
+
+        private
+
+        def through_records_by_owner
+          ActiveRecord::Associations::Preloader.new(
+            owners, through_reflection.name,
+            through_options
+          ).run
+
+          Hash[owners.map do |owner|
+            through_records = Array.wrap(owner.send(through_reflection.name))
+
+            # Dont cache the association - we would only be caching a subset
+            if reflection.options[:source_type] && through_reflection.collection?
+              owner.association(through_reflection.name).reset
+            end
+
+            [owner, through_records]
+          end]
+        end
+
+        def through_options
+          through_options = {}
+
+          if options[:source_type]
+            through_options[:conditions] = { reflection.foreign_type => options[:source_type] }
+          else
+            if options[:conditions]
+              through_options[:include]    = options[:include] || options[:source]
+              through_options[:conditions] = options[:conditions]
+            end
+
+            through_options[:order] = options[:order]
+          end
+
+          through_options
+        end
+      end
+    end
+  end
+end