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

i can't head around one. want validate whether third variable on cakephp form less or equal difference between 2 other variables on form. has tackled or similar?

paul

here code show 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: second rule plain wrong, have tried number of things, coming rubbish:

public $validate = array(      'ag1_compl_dist_num'=>array(         'rule' => array('lessthanequalto','ag1_compl_start_number'),         'message' => 'value must less starting number',         'allowempty' => true,         'required' => false     ),     'ag1_compl_remain' => array(         'rule' => array('lessthanequalto','numdifference'),         'message' => 'value must less difference between numbers',         'allowempty' => true,         'required' => false     )  ); 

clearly, call numdifference should have identifies 2 numbers work out difference between..

when do:

'rule' => array('lessthanequalto','numdifference') 

and in lessthanequalto function $compareto = $this->data[$this->name][$otherfield];, numdifference field in data object, not exist.

one way create lessthanequaltodiff method 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 rule:

public $validate = array(     'ag1_compl_remain' => array(         'rule' => array('lessthanequaltodiff', 'ag1_compl_start_number', 'ag1_compl_used_number'),         'message' => 'value must less difference between numbers',         'allowempty' => true,         'required' => false     ) );