Forms and ActiveRecord validation magic

rubyonrails-talk
1

Hi all,

I've been digging through the code which scaffold creates (Rails 2). What I'm am looking for is to determine how does error_messages_for and form_for determine that ActiveRecord object is completely new and should be validated before the user has had a chance to input some data. Basically, the first time the new.html.erb template is run, error_messages_for does not detect any errors even though the object is newly created (in the controller's new method) and does not validate. But if you then enter data into the input boxes and submit the form, highlights the validation errors. So the question is how does it work out when it is being called the first time and should not validate the inputs?

When I was testing, I put a modelObject.valid? call in the beginning of the template and that made it highlight errors even before you had a chance to input any data. So it seems that error_messages_for and form_for detect this in some way. The question is how? I've been digging through the sources and couldn't find anything.

Thanks, gamehack

2

This is because errors are only created after an explicit call to #valid?, #save, or #create.

When you do ARObject.new, nothing has been run and thus nothing has errored out.

Also, there’s a new_record? flag set to true.

Next time you do #save or #valid?, yaml out the object, you’ll see an “errors” attribute filled with the appropriate errors.

Jason

3

Thank you. I realized that the only difference is that the next time the method is called, a all to #save would have been made, which would have triggered the validations which might in turn make obj.errors.count != 0. So the form functions actually check whether the number of errors is 0 or not. Thanks for the tip.

g