Raise ArgumentError when trying to merge relations of different classes

2 files changed, 7 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/relation.rb b/activerecord/lib/active_record/relation.rb
index ff10df96f2..ef480cfb29 100644
--- a/activerecord/lib/active_record/relation.rb
+++ b/activerecord/lib/active_record/relation.rb
@@ -13,6 +13,8 @@ module ActiveRecord
     end
 
     def merge(r)
+      raise ArgumentError, "Cannot merge a #{r.klass.name} relation with #{@klass.name} relation" if r.klass != @klass
+
       joins(r.relation.joins(r.relation)).
         group(r.send(:group_clauses).join(', ')).
         order(r.send(:order_clauses).join(', ')).
diff --git a/activerecord/test/cases/relations_test.rb b/activerecord/test/cases/relations_test.rb
index 61fcc7ca46..cf6708cc8b 100644
--- a/activerecord/test/cases/relations_test.rb
+++ b/activerecord/test/cases/relations_test.rb
@@ -353,4 +353,9 @@ class RelationTest < ActiveRecord::TestCase
       assert_queries(2) { assert posts.first.author }
     end
   end
+
+  def test_invalid_merge
+    assert_raises(ArgumentError) { Post.scoped & Developer.scoped }
+  end
+
 end