Validating third variable on difference between 2 other variables in cakephp - validation

Question

I can't get my head around this one. I want to validate whether a third variable on a cakephp form is less than or equal to the difference between two other variables on the form. Has anyone tackled this or similar?
Paul
here is some code to show what I have done:
public function lessThanEqualTo($check, $otherfield) {
$value = array_values($check);
$compareTo = $this->data[$this->name][$otherfield];
if (!Validation::comparison($value[0], 'lessorequal', $compareTo)) {
return false;
}
else {
return true;
}
}
public function numDifference($startnumber, $usednumber) {
$sn = int($this->data[$this->name][$startnumber]);
$un = int($this->data[$this->name][$usednumber]);
return ($sn - $un);
}
Model contains validation: but the second rule is plain wrong, I have tried a number of things, but I am just coming up with rubbish:
public $validate = array(
'ag1_compl_dist_num'=>array(
'rule' => array('lessThanEqualTo','ag1_compl_start_number'),
'message' => 'Value must be less than starting number',
'allowEmpty' => true,
'required' => false
),
'ag1_compl_remain' => array(
'rule' => array('lessThanEqualTo','numDifference'),
'message' => 'Value must be less than difference between numbers',
'allowEmpty' => true,
'required' => false
)
);
Clearly, the call to numDifference should have something that identifies which two numbers to work out the difference between..

Answer 1

When you do:
'rule' => array('lessThanEqualTo','numDifference')
And then in your lessThanEqualTo function $compareTo = $this->data[$this->name][$otherfield];, you will look for numDifference field in your data object, which does not exist.
One way would be to create a lessThanEqualToDiff method like this:
public function lessThanEqualToDiff ($check, $startfield, $usedfield) {
$value = array_values($check);
$sn = intval($this->data[$this->name][$startfield]);
$un = intval($this->data[$this->name][$usedfield]);
return Validation::comparison($value[0], 'lessorequal', $sn - $un) ;
}
Then your rule:
public $validate = array(
'ag1_compl_remain' => array(
'rule' => array('lessThanEqualToDiff', 'ag1_compl_start_number', 'ag1_compl_used_number'),
'message' => 'Value must be less than difference between numbers',
'allowEmpty' => true,
'required' => false
)
);

Answer 2

So, the validation method should be like this:
public function lessThanEqualToDiff ($check, $startfield, $usedfield) {
$value = array_values($check);
$sn = (int)$this->data[$this->name][$startfield];
$un = (int)$this->data[$this->name][$usedfield]
return Validation::comparison($value[0], 'lessorequal', $sn - $un) ;
}
to use the php int feature correctly. Thanks to Holt and marian0 for their help.