Symfony2 - Set minimum number of embedded forms - symfony

Question

Using the scenario in How to Embed a Collection of Forms, I would like to ensure that a Task always have at least 1 Tag. For my case however, the relationship of Task and Tag is 1:n rather than n:m.
I am particularly concerned on the scenario where all Tags are removed (I'd like to prevent this). How can I ensure that a Task form always have at least 1 Tag?

Answer 1

As pointed out by m0c the solution was indeed to utilize a custom validation constraint. However, I found out that such a constraint validator already exists in Symfony2.1 so I took the liberty of porting it for 2.0 (since some interfaces apparently changed in 2.1).
Here are ported versions (for 2.0) of Bernhard Schussek's Count.php and CountValidator.php for counting collections (see https://github.com/symfony/Validator/tree/master/Constraints).
Count.php
namespace MyVendor\MyBundle\Validator\Constraints;
use Symfony\Component\Validator\Constraint;
use Symfony\Component\Validator\Exception\MissingOptionsException;
/**
* #Annotation
*
* #api
*/
class Count extends Constraint
{
public $minMessage = 'This collection should contain {{ limit }} elements or more.';
public $maxMessage = 'This collection should contain {{ limit }} elements or less.';
public $exactMessage = 'This collection should contain exactly {{ limit }} elements.';
public $min;
public $max;
public function __construct($options = null)
{
if (null !== $options && !is_array($options)) {
$options = array(
'min' => $options,
'max' => $options,
);
}
parent::__construct($options);
if (null === $this->min && null === $this->max) {
throw new MissingOptionsException('Either option "min" or "max" must be given for constraint ' . __CLASS__, array('min', 'max'));
}
}
}
CountValidator.php
namespace MyVendor\MyBundle\Validator\Constraints;
use Symfony\Component\Validator\Constraint;
use Symfony\Component\Validator\ConstraintValidator;
use Symfony\Component\Validator\Exception\UnexpectedTypeException;
class CountValidator extends ConstraintValidator
{
/**
* {#inheritDoc}
*/
public function isValid($value, Constraint $constraint)
{
if (null === $value) {
return false;
}
if (!is_array($value) && !$value instanceof \Countable) {
throw new UnexpectedTypeException($value, 'array or \Countable');
}
$count = count($value);
if ($constraint->min == $constraint->max
&& $count != $constraint->min) {
$this->setMessage($constraint->exactMessage, array(
'{{ count }}' => $count,
'{{ limit }}' => $constraint->min,
));
return false;
}
if (null !== $constraint->max && $count > $constraint->max) {
$this->setMessage($constraint->maxMessage, array(
'{{ count }}' => $count,
'{{ limit }}' => $constraint->min,
));
return false;
}
if (null !== $constraint->min && $count < $constraint->min) {
$this->setMessage($constraint->minMessage, array(
'{{ count }}' => $count,
'{{ limit }}' => $constraint->min,
));
return false;
}
return true;
}
}

Answer 2

I would create a custom Validator which checks if the property where the relationshop is mapped to on entity level has some elements in the collection.
And the Validator fails:
public function isValid($value, Constraint $constraint)
{
if (count($value) <1 ) {
//also define a message for your custom validator
$this->setMessage($constraint->message, array('%string%' => $value));
return false;
}
return true;
}
For instructions how to implement this custom validator: http://symfony.com/doc/current/cookbook/validation/custom_constraint.html

Answer 3

do u want to just validate upon posting, wheter or not there is atleast 1 tag,
or do u want the form to actually already have 1 empty tag in it upon loading ?
(wich i assume bacause u say "how can I ensure that a Task form always have at least 1 Tag?")
if u need the second, just
$tag1 = new Tag();
$tag1->name = 'tag1';
$task->getTags()->add($tag1);
Before
$form = $this->createForm(new TaskType(), $task);
like the docs say..