merge parent joins for through associations

activerecord/CHANGELOG.md

@@ -1,7 +1,13 @@
 ## Rails 5.0.0.rc1 (May 06, 2016) ##
 
-*   No changes.
+*   Merge parent joins for through associations.
 
+    Merges parent associations joins for through associations into a scope. Previously joins in association scope were
+    taken into account only for root associations with that scope.
+
+    Fixes #22538.
+
+    *Seva Orlov*
 
 ## Rails 5.0.0.beta4 (April 27, 2016) ##
 

activerecord/lib/active_record/associations/association_scope.rb

@@ -134,13 +134,13 @@ def add_constraints(scope, owner, association_klass, refl, chain_head, chain_tai
             scope = next_chain_scope(scope, table, reflection, association_klass, foreign_table, next_reflection)
           end
 
-          # Exclude the scope of the association itself, because that
-          # was already merged in the #scope method.
           reflection.constraints.each do |scope_chain_item|
-            item  = eval_scope(reflection.klass, scope_chain_item, owner)
+            item = eval_scope(reflection.klass, scope_chain_item, owner)
 
             if scope_chain_item == refl.scope
               scope.merge! item.except(:where, :includes)
+            elsif item.joins_values.any?
+              merge_joins(scope, item)
             end
 
             reflection.all_includes do
@@ -158,6 +158,21 @@ def add_constraints(scope, owner, association_klass, refl, chain_head, chain_tai
         scope
       end
 
+      # Merges inner joins from `other` relation to `scope` relation.
+      def merge_joins(scope, other)
+        association_joins, rest_joins = other.joins_values.partition do |join|
+          case join
+          when Hash, Symbol, Array
+            true
+          else
+            false
+          end
+        end
+
+        join_dependency = ActiveRecord::Associations::JoinDependency.new(other.klass, association_joins, rest_joins)
+        scope.joins! join_dependency.join_constraints([], Arel::Nodes::InnerJoin).map(&:joins)
+      end
+
       def eval_scope(klass, scope, owner)
         klass.unscoped.instance_exec(owner, &scope)
       end

activerecord/test/cases/associations/has_many_through_associations_test.rb

@@ -1215,4 +1215,13 @@ def test_has_many_through_do_not_cache_association_reader_if_the_though_method_h
   ensure
     TenantMembership.current_member = nil
   end
+
+  def test_has_many_through_with_joins_in_scope
+    developer = Developer.create! name: 'Jamis'
+    post = Post.first
+    author = Author.create! name: 'John'
+    Comment.create! developer: developer, post: post, body: '', author: author
+
+    assert_includes post.reload.jamises_developer_comments_authors, author
+  end
 end

activerecord/test/models/post.rb

@@ -60,6 +60,9 @@ def the_association
     end
   end
 
+  has_many :jamises_developer_comments, -> { joins(:developer).merge(Developer.jamises) }, class_name: 'Comment'
+  has_many :jamises_developer_comments_authors, through: :jamises_developer_comments, source: :author, source_type: 'Author'
+
   has_many :comments_with_extend, extend: NamedExtension, class_name: "Comment", foreign_key: "post_id" do
     def greeting
       "hello"