form validation behavior

hello.

first sorry my english , it's not my native language.

I am using form validation successfully, but I have a problem with the rule is_unique when I want to edit the object. For example I have de user field with value "edel" ,of course it should be unique. When I load the view edit and I don't change the field user the form validation catch the error for this field because "edel" user exists in database but it's the same instance that I am editing.

so how can i avoid this behavior in editing views