validate uniqueness with limit in utf8

[#2653 state:committed]

Signed-off-by: Jeremy Kemper <jeremy@bitsweat.net>

activerecord/lib/active_record/validations/uniqueness.rb

@@ -119,7 +119,7 @@ def validates_uniqueness_of(*attr_names)
             comparison_operator = "IS ?"
           elsif column.text?
             comparison_operator = "#{connection.case_sensitive_equality_operator} ?"
-            value = column.limit ? value.to_s[0, column.limit] : value.to_s
+            value = column.limit ? value.to_s.mb_chars[0, column.limit] : value.to_s
           else
             comparison_operator = "= ?"
           end

activerecord/test/cases/validations/uniqueness_validation_test.rb

@@ -238,6 +238,16 @@ def test_validate_uniqueness_with_limit
     assert !e2.valid?, "Created an event whose title, with limit taken into account, is not unique"
   end
 
+  def test_validate_uniqueness_with_limit_and_utf8
+    with_kcode('UTF8') do
+      # Event.title is limited to 5 characters
+      e1 = Event.create(:title => "一二三四五")
+      assert e1.valid?, "Could not create an event with a unique, 5 character title"
+      e2 = Event.create(:title => "一二三四五六七八")
+      assert !e2.valid?, "Created an event whose title, with limit taken into account, is not unique"
+    end
+  end
+
   def test_validate_straight_inheritance_uniqueness
     w1 = IneptWizard.create(:name => "Rincewind", :city => "Ankh-Morpork")
     assert w1.valid?, "Saving w1"