Extract JoinDependency#join_relation to DRY the repeated application of the #join_associations.

activerecord/lib/active_record/associations/join_dependency.rb

@@ -55,6 +55,13 @@ def join_base
         join_parts.first
       end
 
+      def join_relation(relation)
+        join_associations.each do |association|
+          relation = association.join_relation(relation)
+        end
+        relation
+      end
+
       def columns
         join_parts.collect { |join_part|
           table = join_part.aliased_table

activerecord/lib/active_record/relation/finder_methods.rb

@@ -225,10 +225,7 @@ def construct_relation_for_association_find(join_dependency)
 
     def apply_join_dependency(relation, join_dependency)
       relation = relation.except(:includes, :eager_load, :preload)
-
-      join_dependency.join_associations.each do |association|
-        relation = association.join_relation(relation)
-      end
+      relation = join_dependency.join_relation(relation)
 
       if using_limitable_reflections?(join_dependency.reflections)
         relation

activerecord/lib/active_record/relation/merger.rb

@@ -94,9 +94,7 @@ def merge_joins
                                                                            [])
           relation.joins! rest
 
-          join_dependency.join_associations.each do |association|
-            @relation = association.join_relation(relation)
-          end
+          @relation = join_dependency.join_relation(relation)
         end
       end