On the Refulz blog there's a post showing you how to set up conditional multiple validation rules in a Yii framework application.

I am yet to write the last article of the Yii Session series. I just decided to write something about the scenarios in the Validation feature of Yii framework. Scenarios are a very useful tool for adding different validations rules for different cases on the same model. In a real life situation, you would require one validation rule for user registration but the same rule might not be applicable to the User login. Scenarios help you define validation rules for different situations within same model.

He shows you how to set up a "rules()" method in your model and a few validation configurations inside it - ensuring the password and email are set, checking the length of the password, etc. Then, by calling the "validate()" method on the model, you can easily apply these rules and check the pass/fail status.