support finding by a ruby class [#5979 state:resolved]

activerecord/lib/active_record/relation/predicate_builder.rb

@@ -27,6 +27,9 @@ module ActiveRecord
             attribute.in(value)
           when ActiveRecord::Base
             attribute.eq(value.quoted_id)
+          when Class
+            # FIXME: I think we need to deprecate this behavior
+            attribute.eq(value.name)
           else
             attribute.eq(value)
           end

activerecord/test/cases/relations_test.rb

@@ -438,6 +438,13 @@ class RelationTest < ActiveRecord::TestCase
     assert_equal author, authors.first
   end
 
+  class Mary < Author; end
+
+  def test_find_by_classname
+    Author.create!(:name => Mary.name)
+    assert_equal 1, Author.where(:name => Mary).size
+  end
+
   def test_find_by_id_with_list_of_ar
     author = Author.first
     authors = Author.find_by_id([author])