HABTM form validation in CakePHP

Question

I have a Projects table and a Users table which are linked by a HABTM relation. In the \"add\" new Project page I have a multiple checkbox section to select Users for the ne

Answer 1

2016 update for CakePhp 2.7

Full answer here : HABTM form validation with CakePHP 2.x

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TL;DR;

AppModel.php

public function beforeValidate($options = array()){
   foreach (array_keys($this->hasAndBelongsToMany) as $model){
     if(isset($this->data[$model][$model]))
       $this->data[$this->name][$model] = $this->data[$model][$model];
   }
   return true;
 }

 public function afterValidate($options = array()){
   foreach (array_keys($this->hasAndBelongsToMany) as $model){
     unset($this->data[$this->name][$model]);
     if(isset($this->validationErrors[$model]))
       $this->$model->validationErrors[$model] = $this->validationErrors[$model];
   }
   return true;
 }

In the main model of your HABTM :

public $validate = array(
    'Tag' => array(
        'rule' => array('multiple', array('min' => 1)),
        'required' => true,
        'message' => 'Please select at least one Tag for this Post.'
        )
    );