Add CollectionProxy#scope

This can be used to get a Relation from an association.

Previously we had a #scoped method, but we're deprecating that for
AR::Base, so it doesn't make sense to have it here.

This was requested by DHH, to facilitate code like this:

    Project.scope.order('created_at DESC').page(current_page).tagged_with(@tag).limit(5).scoping do
      @topics      = @project.topics.scope
      @todolists   = @project.todolists.scope
      @attachments = @project.attachments.scope
      @documents   = @project.documents.scope
    end

1 files changed, 7 insertions, 0 deletions

diff --git a/activerecord/test/cases/associations_test.rb b/activerecord/test/cases/associations_test.rb
index b7c2bcad00..c0f1945cec 100644
--- a/activerecord/test/cases/associations_test.rb
+++ b/activerecord/test/cases/associations_test.rb
@@ -218,6 +218,13 @@ class AssociationProxyTest < ActiveRecord::TestCase
   def test_scoped_allows_conditions
     assert developers(:david).projects.merge!(where: 'foo').where_values.include?('foo')
   end
+
+  test "getting a scope from an association" do
+    david = developers(:david)
+
+    assert david.projects.scope.is_a?(ActiveRecord::Relation)
+    assert_equal david.projects, david.projects.scope
+  end
 end
 
 class OverridingAssociationsTest < ActiveRecord::TestCase