Ensure that has_many :through associations use a count query instead of loading the target when #size is called. Closes #8800 [lifo]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@7237 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

1 files changed, 7 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/associations/has_many_through_association.rb b/activerecord/lib/active_record/associations/has_many_through_association.rb
index ebe1be04e5..ec093548da 100644
--- a/activerecord/lib/active_record/associations/has_many_through_association.rb
+++ b/activerecord/lib/active_record/associations/has_many_through_association.rb
@@ -96,6 +96,13 @@ module ActiveRecord
         end
       end
 
+      # Returns the size of the collection by executing a SELECT COUNT(*) query if the collection hasn't been loaded and
+      # calling collection.size if it has. If it's more likely than not that the collection does have a size larger than zero
+      # and you need to fetch that collection afterwards, it'll take one less SELECT query if you use length.
+      def size
+        loaded? ? @target.size : count
+      end
+
       # Calculate sum using SQL, not Enumerable
       def sum(*args, &block)
         calculate(:sum, *args, &block)