php - Form element validation based on other form element -

i'm rendering form add class (course) database. class has starttime , endttime. both time of day fields. created fieldset class:

<?php namespace admin\form;  use zend\form\fieldset; use zend\inputfilter\inputfilterinterface; use zend\inputfilter\inputfilterproviderinterface;  class artclassfieldset extends fieldset implements inputfilterproviderinterface {     public function __construct()     {         parent::__construct('artclass');          $this->add(array(             'name'          => 'dayofweek',             'type'          => 'zend\form\element\select',             'options'       => array(                 'label'             => 'day of week:',                 'value_options'     => array(                     1           => 'monday',                     2           => 'tuesday',                     3           => 'wednesday',                     4           => 'thursday',                     5           => 'friday',                     6           => 'saturday',                 ),             ),         ));          $this->add(array(                 'name' => 'starttime',                 'type' => 'zend\form\element\time',                 'options' => array(                     'label' => 'start time:',                     'format' => 'h:ia',                 ),             )         );          $this->add(array(                 'name' => 'endtime',                 'type' => 'zend\form\element\time',                 'options' => array(                     'label' => 'end time:',                     'format' => 'h:ia',                 ),             )         );          $this->add(array(                 'name' => 'teacher',                 'type' => 'admin\form\teacherselectorfieldset',                 'options' => array(                     'label' => 'teacher:',                 )             )         );     }      public function getinputfilterspecification()     {         return array(                 'dayofweek' => array(                     'required' => true,                     'filters' => array(                         array('name' => 'int'),                     ),                     'validators' => array(                         array(                             'name' => 'between',                             'break_chain_on_failure' => true,                             'options' => array(                                 'min' => 1,                                 'max' => 6,                              ),                         ),                     ),                 ),                 'starttime' => array(                     'required' => true,                 ),                 'endtime' => array(                     'required' => true,                 ),                 'teacher' => array(                 ),         );     } } 

in form class add fieldset form:

<?php  namespace admin\form;  use zend\form\form;  class artclassadd extends form {     public function __construct()     {         parent::__construct("artclass-add");         $this->setattribute('action', '/admin/artclass/add');         $this->setattribute('method', 'post');          $this->add(array(                 'type' => 'admin\form\artclassfieldset',                 'options' => array('use_as_base_fieldset' => true)             )         );          $this->add(array(                 'name' => 'submit',                 'attributes' => array(                     'type' => 'submit',                     'value' => 'save'                                    )             )         );     } } 

the format of 2 time fields 'h:ia' means '11:00am'. validate starttime before endtime. question how do that? i'm thinking should use zend\validator\callback, not sure.

you're on right track. have use callback validator. use endtime input spec:

return array(     'endtime' => array(         'required' => true,         'validators' => array(             array(                 'name' => 'callback',                 'options' => array(                     'callback' => function($value, $context)                     {                         $endtime = datetime::createfromformat'h:ia', $value);                         $starttime = datetime::createfromformat('h:ia', $context['starttime']);                         return $endtime > $starttime;                     }                 ),             ),         ),     ), );