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

activerecord/CHANGELOG.md

 ## Rails 4.0.0 (unreleased) ##
 
+*   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
+
+    *Jon Leighton*
+
 *   Add `Relation#load`
 
     This method explicitly loads the records and then returns `self`.

activerecord/lib/active_record/associations/collection_proxy.rb

@@ -855,7 +855,8 @@ def scoping
         @association.scoped.scoping { yield }
       end
 
-      def spawn
+      # Returns a <tt>Relation</tt> object for the records in this association
+      def scope
         association = @association
 
         @association.scoped.extending! do
@@ -863,6 +864,9 @@ def spawn
         end
       end
 
+      # :nodoc:
+      alias spawn scope
+
       # Equivalent to <tt>Array#==</tt>. Returns +true+ if the two arrays
       # contain the same number of elements and if each element is equal
       # to the corresponding element in the other array, otherwise returns

activerecord/test/cases/associations_test.rb

@@ -218,6 +218,13 @@ def test_proxy_association_accessor
   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