DateTime fields in doctrine and Symfony 2

The hidden file type is just a text field which is hidden.

This means that, in order to render the widget, it just uses the simple widget template (see include statement in hidden_widget.html):

<input type="<?php echo isset($type) ? $view->escape($type) : 'text' ?>" <?php echo $view['form']->block($form, 'widget_attributes') ?><?php if (!empty($value) || is_numeric($value)): ?> value="<?php echo $view->escape($value) ?>"<?php endif ?> />

As you can see it just echo's the value you passed to the field (the escape function does not to any important things). There is the problem: You passed a DateTime class as value, not a string. Even though you specified you passed a DateTime class, it's still not changing the value and it just tries to convert the DateTime object into a string. That isn't possible.

That's what currently happends. Now, let's move onto how to get it fixed. The data it tries to render ($value) is actually called the view data (as you see where the variable is defined). In the current situation, the view data is equal to the Form::$viewData property (see the ->getViewData() definition). This property is defined previously by the ->normToView() method (see the $viewData definition).

As you can see in the ->normToView() method, it runs the view transformers if available:

foreach ($this->config->getViewTransformers() as $transformer) {
    $value = $transformer->transform($value);
}

So in order to convert the DateTime object to a string, we have to use a View transformer. Now, let's take a look at the available data transformers. We are very lucky as there is a DateTimeToStringTransformer:

/**
 * Transforms between a date string and a DateTime object
 *
 * @author Bernhard Schussek <[email protected]>
 * @author Florian Eckerstorfer <[email protected]>
 */
class DateTimeToStringTransformer extends BaseDateTimeTransformer
{

That's just what we needed!

Now, let's register this data transformer as a view transformer to the hidden field:

use Symfony\Component\Form\Extension\Core\DataTransformer\DateTimeToStringTransformer;

// ...

$builder = $this->createFormBuilder($myClass);
$builder->add(
    $builder->create('myDate', 'hidden')
        ->addViewTransformer(new DateTimeToStringTransformer())
);

And after you've done this, the form should be correctly generated. And because, almost everything in the form is symmetric, the transformer also works from string to datetime, meaning that your code only uses the DateTime object!