Question

Is there a way to validate data (using CakePHP’s model validation) to make sure that at least “a” or “b” has data (does not have to have data in both).

Answer 1

In your model, do something like this. The function will be called when you perform a save operation.

EDITED

public $validate = array(
    'a' => array(
        'customCheck' => array(
            'rule' => 'abCheck',
            'message' => 'You must enter data in a or b.'
        )
    ),
    'b' => array(
        'customCheck' => array(
            'rule' => 'abCheck',
            'message' => 'You must enter data in a or b.'
        )
    )
);

//Function must be public for Validator to work
//Checks to see if either a or b properties are set and not empty
public function abCheck(){
    if((isset($this->data['Model']['a']) && !empty($this->data['Model']['a'])) || (isset($this->data['Model']['b']) && !empty($this->data['Model']['b']))){
         return true;
    }
    return false;
}