Validation on before_add callback

Rails
1

problem: validation error is not functionning in callback

callback for many-to-many association:

keyword.rb

:before_add => :reject_self_related

def reject_self_related(related_keyword)
    if (related_keyword == self)

this does not work:

        errors.add(:name, "Relating a keyword to itself is

forbidden!")
raise “Relating a keyword to itself is forbidden!”
end
end

in the keyword.rhtml form:

<%= error_messages_for ‘keyword’ %>

does not display the error message.

what am I doing wrong?

2

Isabelle wrote:

Hi Isabelle,

First off, is the callback being triggered at all ? If you replace the
whole body with the raise, do you see the exception ?

Second, if you just replace the body with the errors.add, do you see the
error ?

Last, == on Object tests for the exact same Object, I think ActiveRecord
override this to compare ids, if the new item hasn’t yet been saved, the
== method will return false. Perhaps you need to check, say
keyword.text, or whatever the property is that stores the text.

Alan

3

Alan F. wrote:

Isabelle wrote:

Hi Isabelle,

First off, is the callback being triggered at all ? If you replace the
whole body with the raise, do you see the exception ?

yes. I can catch the exception in the controller and display the
exception message:

keywords_controller.rb

    # attempt to add item to list
    begin
      @keyword.related_keywords<< @related
    rescue Exception
      # extract error messages from the global variable
      # representing the Exception object
      flash[:notice] = $!.message
    end

Second, if you just replace the body with the errors.add, do you see the
error ?

no, and the object that should not have been saved is saved.

Last, == on Object tests for the exact same Object, I think ActiveRecord
override this to compare ids, if the new item hasn’t yet been saved, the
== method will return false. Perhaps you need to check, say
keyword.text, or whatever the property is that stores the text.

I see your point. In my case the callback is before adding an existing
item to a collection that is defined as a self-referential
has_and_belongs_to_many relation.

4

Alan F. wrote:

I see your point. In my case the callback is before adding an existing
item to a collection that is defined as a self-referential
has_and_belongs_to_many relation.

I’d reckon that’s the problem then, and would compare the attribute,
rather than the object.

tried it and still the errors.add() is not executed

5

I see your point. In my case the callback is before adding an existing
item to a collection that is defined as a self-referential
has_and_belongs_to_many relation.

I’d reckon that’s the problem then, and would compare the attribute,
rather than the object.