Move constructing join scope to `Reflection`

2 files changed, 12 insertions, 13 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
index 7fa62bfa5f..95f16c622e 100644
--- a/activerecord/lib/active_record/associations/join_dependency/join_association.rb
+++ b/activerecord/lib/active_record/associations/join_dependency/join_association.rb
@@ -40,15 +40,7 @@ module ActiveRecord
 
             constraint = build_constraint(klass, table, key, foreign_table, foreign_key)
 
-            predicate_builder = reflection.predicate_builder(table)
-            scope_chain_items = reflection.join_scopes(table, predicate_builder)
-            klass_scope       = reflection.klass_join_scope(table, predicate_builder)
-
-            scope_chain_items.concat [klass_scope].compact
-
-            rel = scope_chain_items.inject(scope_chain_items.shift) do |left, right|
-              left.merge right
-            end
+            rel = reflection.join_scope(table)
 
             if rel && !rel.arel.constraints.empty?
               binds += rel.bound_attributes
diff --git a/activerecord/lib/active_record/reflection.rb b/activerecord/lib/active_record/reflection.rb
index c4b58386fa..c6aa2ed720 100644
--- a/activerecord/lib/active_record/reflection.rb
+++ b/activerecord/lib/active_record/reflection.rb
@@ -185,6 +185,14 @@ module ActiveRecord
       end
       deprecate :scope_chain
 
+      def join_scope(table)
+        predicate_builder = predicate_builder(table)
+        scope_chain_items = join_scopes(table, predicate_builder)
+        klass_scope       = klass_join_scope(table, predicate_builder)
+
+        scope_chain_items.inject(klass_scope || scope_chain_items.shift, &:merge!)
+      end
+
       def join_scopes(table, predicate_builder) # :nodoc:
         if scope
           [build_scope(table, predicate_builder).instance_exec(&scope)]
@@ -286,16 +294,15 @@ module ActiveRecord
         Relation.create(klass, table, predicate_builder)
       end
 
-      def predicate_builder(table)
-        PredicateBuilder.new(TableMetadata.new(klass, table))
-      end
-
       protected
         def actual_source_reflection # FIXME: this is a horrible name
           self
         end
 
       private
+        def predicate_builder(table)
+          PredicateBuilder.new(TableMetadata.new(klass, table))
+        end
 
         def join_pk(_)
           foreign_key