Showing a warning message when before_create fails?

In one of my models, I have a before_create attribute that se开发者_开发技巧ts a particular value, fetched from a web API. However, this before_create returns false, killing the model creation, if no results are found when using the API.

This works fine, but I would like to also show a warning message, so that the users know their input was not accepted. How would I go about doing this?

A before_create isn't the right place to be reporting errors. Your before_create should try to set the value and then a validator should check if it is there, if the validator doesn't find the value then you'll get your error message and such. So, if your attribute is called pancakes, then you'd have something like this:

before_validation :stuff_web_api_value_into_pancakes, :if => :new_record?
validates_presence_of :pancakes

You could, of course, use a different validator than validates_presence_of, that's just there for illustrative purposes. And you'll want a before_validation hook to get things to happen in the right order, the :if => :new_record? will only run the hook when you're creating a new model.