From edd94cee9af1688dd036fc58fd405adb30a5e0da Mon Sep 17 00:00:00 2001
From: Jon Leighton <j@jonathanleighton.com>
Date: Fri, 9 Nov 2012 12:09:37 +0000
Subject: Delegate all calculations to the scope.

So that the scope may be a NullRelation and return a result without
executing a query.

Fixes #7928
---
 activerecord/lib/active_record/associations/collection_proxy.rb    | 6 ++----
 activerecord/lib/active_record/null_relation.rb                    | 4 ++++
 activerecord/test/cases/associations/has_many_associations_test.rb | 1 +
 3 files changed, 7 insertions(+), 4 deletions(-)

(limited to 'activerecord')

diff --git a/activerecord/lib/active_record/associations/collection_proxy.rb b/activerecord/lib/active_record/associations/collection_proxy.rb
index e044099b72..1b746b46b7 100644
--- a/activerecord/lib/active_record/associations/collection_proxy.rb
+++ b/activerecord/lib/active_record/associations/collection_proxy.rb
@@ -28,6 +28,8 @@ module ActiveRecord
     # is computed directly through SQL and does not trigger by itself the
     # instantiation of the actual post records.
     class CollectionProxy < Relation
+      delegate *ActiveRecord::Calculations.public_instance_methods, to: :scope
+
       def initialize(association) #:nodoc:
         @association = association
         super association.klass, association.klass.arel_table
@@ -965,10 +967,6 @@ module ActiveRecord
         proxy_association.reload
         self
       end
-
-      def pluck(column_names)
-        scope.pluck(column_names)
-      end
     end
   end
 end
diff --git a/activerecord/lib/active_record/null_relation.rb b/activerecord/lib/active_record/null_relation.rb
index f8f7a6c976..711fc8b883 100644
--- a/activerecord/lib/active_record/null_relation.rb
+++ b/activerecord/lib/active_record/null_relation.rb
@@ -50,6 +50,10 @@ module ActiveRecord
       0
     end
 
+    def sum(*)
+      0
+    end
+
     def calculate(_operation, _column_name, _options = {})
       nil
     end
diff --git a/activerecord/test/cases/associations/has_many_associations_test.rb b/activerecord/test/cases/associations/has_many_associations_test.rb
index baf07f352e..aae93bb9d0 100644
--- a/activerecord/test/cases/associations/has_many_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_associations_test.rb
@@ -1656,6 +1656,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
       assert_equal [], post.comments
       assert_equal [], post.comments.where(body: 'omg')
       assert_equal [], post.comments.pluck(:body)
+      assert_equal 0,  post.comments.sum(:id)
     end
   end
 end
-- 
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