The problem

Sample posts/view.ctp

View Template:


<div class="post">
<h2><?php  __('Post');?></h2>

<?php echo $post['Post']['body']?>

<fieldset>
<?php 
echo $form->create('Comment');
echo('<legend>'.__('Add comment',true).'<legend>');
echo $form->input('title');
echo $form->input('body');
echo $form->input('author_name');
echo $form->input('author_email');
echo $form->input('author_url');
echo $form->end('submit')
?>
</fieldset>

</div>

I've hit this problem more than once, a nice way around it is to use AJAX to call up and submit the form, just like the bakery does - however ajax is not always an option, so poLK and i have come up with a very nice solution, even if i do say so myself!

The solution

Session to the rescue, after puzzling over this for a while and talking with a few people on #cakephp it seemed that the simplest and quickest solution was going to be to set the validation data into the session from the validating controller (e.g. Comments) and then pull it out later in the viewing controller (e.g. Posts) ready to be displayed.

So thats exactly what we've done, we created function called _persistValidation to simplify getting and setting the data to the session.

Add the following function to your app_controller.php

Controller Class:

<?php 
/**
     * Called with some arguments (name of default model, or model from var $uses),
     * models with invalid data will populate data and validation errors into the session.
     *
     * Called without arguments, it will try to load data and validation errors from session 
     * and attach them to proper models. Also merges $data to $this->data in controller.
     * 
     * @author poLK
     * @author drayen aka Alex McFadyen
     * 
     * Licensed under The MIT License
     * @license            http://www.opensource.org/licenses/mit-license.php The MIT License
     */
    function _persistValidation() {
        $args = func_get_args();
        
        if (empty($args)) {
            if ($this->Session->check('Validation')) {
                $validation = $this->Session->read('Validation');
                $this->Session->del('Validation');
                foreach ($validation as $modelName => $sessData) {
                    if ($this->name != $sessData['controller']){
                        if (in_array($modelName, $this->modelNames)) {
                            $Model =& $this->{$modelName};
                        } elseif (ClassRegistry::isKeySet($modelName)) {
                            $Model =& ClassRegistry::getObject($modelName);
                        } else {
                            continue;
                        }
        
                        $Model->data = $sessData['data'];
                        $Model->validationErrors = $sessData['validationErrors'];
                        $this->data = Set::merge($sessData['data'],$this->data);
                    }
                }
            }
        } else {
            foreach($args as $modelName) {
                if (in_array($modelName, $this->modelNames) && !empty($this->{$modelName}->validationErrors)) {
                        $this->Session->write('Validation.'.$modelName, array(
                                                        'controller'            =>    $this->name,
                                                        'data'                     => $this->{$modelName}->data,
                                                        'validationErrors'     => $this->{$modelName}->validationErrors
                        ));
                }
            }
        }
    }
?>
We also wanted to make the act of pulling the data out of the session seamless, so no additional code would be needed in the viewing controller (Posts), so were going to pull out the data automatically, using beforeRender().

Add the following function to your viewing controller or app_contoller.php (if your lazy, like all good programmers are, and want it enabled for all controllers).

Controller Class:

<?php 
    function beforeRender(){
        $this->_persistValidation();
    }
?>
With that in place, all you need to do is call _persistValidation, from your validating controller (Comments) before you redirect e.g.

Controller Class:

<?php 
    function add() {
        if (!empty($this->data)) {
            $this->cleanUpFields();
            
            $this->Comment->create();
            if ($this->Comment->save($this->data)) {
                $this->Session->setFlash('The Comment has been saved');
            } else {
                $this->_persistValidation('Comment');
                $this->Session->setFlash('The Comment could not be saved. Please correct the errors and try again.');
            }
        }
        $this->redirect($this->referer(), null, true);
    }
?>
Yup, its that simple, just $this->_persistValidation('Comment'); and your done!!

Enjoy

Gotchas

In most situations this should just work, but there are situations where it can cause problems.

Say you have Post->Message and Message->UserTo Message->UserFrom, after a restore, both UserTo and UserFrom (as they are references to one model instance) will be initialized with the correct data, BUT not with array('UserTo'=> etc - instead with array('User' =>
There may be others, please if you find them and or any improvements let me know and i will update the tutorial.