pass the preloader down so we only have to construct one

activerecord/lib/active_record/associations/preloader.rb

@@ -93,7 +93,7 @@ def preload(records, associations, preload_scope = nil)
         else
           associations.flat_map { |association|
             preloaders_on association, records, preload_scope
-          }.each(&:run)
+          }
         end
       end
 
@@ -133,7 +133,9 @@ def preloaders_for_hash(association, records, scope)
       def preloaders_for_one(association, records, scope)
         grouped_records(association, records).flat_map do |reflection, klasses|
           klasses.map do |rhs_klass, rs|
-            preloader_for(reflection).new(rhs_klass, rs, reflection, scope)
+            loader = preloader_for(reflection).new(rhs_klass, rs, reflection, scope)
+            loader.run self
+            loader
           end
         end
       end

activerecord/lib/active_record/associations/preloader/association.rb

@@ -20,13 +20,13 @@ def initialize(klass, owners, reflection, preload_scope)
           @loaded = false
         end
 
-        def run
+        def run(preloader)
           unless owners.first.association(reflection.name).loaded?
-            preload
+            preload(preloader)
           end
         end
 
-        def preload
+        def preload(preloader)
           raise NotImplementedError
         end
 
@@ -73,7 +73,7 @@ def options
         end
 
         def preloaded_records
-          associated_records_by_owner.values.flatten
+          @associated_records_by_owner.values.flatten
         end
 
         def loaded?
@@ -82,7 +82,7 @@ def loaded?
 
         private
 
-        def associated_records_by_owner
+        def associated_records_by_owner(preloader)
           @loaded = true
 
           return @associated_records_by_owner if @associated_records_by_owner

activerecord/lib/active_record/associations/preloader/collection_association.rb

@@ -9,8 +9,8 @@ def build_scope
           super.order(preload_scope.values[:order] || reflection_scope.values[:order])
         end
 
-        def preload
-          associated_records_by_owner.each do |owner, records|
+        def preload(preloader)
+          associated_records_by_owner(preloader).each do |owner, records|
             association = owner.association(reflection.name)
             association.loaded!
             association.target.concat(records)

activerecord/lib/active_record/associations/preloader/has_and_belongs_to_many.rb

@@ -34,7 +34,7 @@ def association_key
         # Once we have used the join table column (in super), we manually instantiate the
         # actual records, ensuring that we don't create more than one instances of the same
         # record
-        def associated_records_by_owner
+        def associated_records_by_owner(preloader)
           return @associated_records_by_owner if @associated_records_by_owner
 
           records = {}

activerecord/lib/active_record/associations/preloader/has_many_through.rb

@@ -4,7 +4,7 @@ class Preloader
       class HasManyThrough < CollectionAssociation #:nodoc:
         include ThroughAssociation
 
-        def associated_records_by_owner
+        def associated_records_by_owner(preloader)
           return @associated_records_by_owner if @associated_records_by_owner
 
           records_by_owner = super

activerecord/lib/active_record/associations/preloader/singular_association.rb

@@ -5,8 +5,8 @@ class SingularAssociation < Association #:nodoc:
 
         private
 
-        def preload
-          associated_records_by_owner.each do |owner, associated_records|
+        def preload(preloader)
+          associated_records_by_owner(preloader).each do |owner, associated_records|
             record = associated_records.first
 
             association = owner.association(reflection.name)

activerecord/lib/active_record/associations/preloader/through_association.rb

@@ -11,15 +11,14 @@ def source_reflection
           reflection.source_reflection
         end
 
-        def associated_records_by_owner
+        def associated_records_by_owner(preloader)
           @loaded = true
 
           return @associated_records_by_owner if @associated_records_by_owner
 
-          left_loader = Preloader.new
-          left_loader.preload(owners,
-                              through_reflection.name,
-                              through_scope)
+          preloader.preload(owners,
+                            through_reflection.name,
+                            through_scope)
 
           should_reset = (through_scope != through_reflection.klass.unscoped) ||
              (reflection.options[:source_type] && through_reflection.collection?)
@@ -37,10 +36,9 @@ def associated_records_by_owner
 
           middle_records = through_records.map { |(_,rec,_)| rec }.flatten
 
-          preloader = Preloader.new
           preloaders = preloader.preload(middle_records,
-                            source_reflection.name,
-                            reflection_scope)
+                                         source_reflection.name,
+                                         reflection_scope)
 
           middle_to_pl = preloaders.each_with_object({}) do |pl,h|
             pl.owners.each { |middle|