How to avoid empty values from checkbox list by using EntityType form type?

Question

I have a form field like this:

$form->add('tags', EntityType:class, array(
    'class' => Tags::class,
    'multiple' => true,
    'expanded' => true,
    'required' => true,
));

This render a nice checkbox list and I need to ensure that at least one option is selected after submiting the form, but even if the required option is true it doesn't work, I tried with NotBlank() and NotNull() constraints, also doesn't work (i.e. the form is valid).

How to avoid empty values from checkbox list by using EntityType form type?

Answer 1

You can use the Count constraint.

In your entity class:

/**
 * @Assert\Count(
 *      min = "1",
 *      minMessage = "You must specify at least one tag"
 * )
 */
protected $tags

Note that you can specify a max parameter and the according message.

Also, the required option only add required to your field on the client side, it does nothing on the server side.