Symfony get onetomany entity values in form field

Question

There are Service and Tag entities with ManyToMany relationship.

  class Service {
       /**
        * @ORM\ManyToMany(targetEntity="Tag", mappedBy="serviceList",cascade={"persist"})
        */
       private $tagList;
  }

  class Tag{
        /**
         * @var string
         */
        private $name;

        /**
         * @ORM\ManyToMany(targetEntity="Service", inversedBy="tagList")
         * @ORM\JoinTable(name="tags_services")
         */
        private $serviceList;
 }

Here is ServiceType

public function buildForm(FormBuilderInterface $builder, array $options)
{
    $builder
        ->add('title', TextType::class, array(
            'label' => 'Title',
        ))
        ->add('tags', TextType::class, array(
            'label' => 'Tags',
            'mapped'   => false
        ))
    ;
}

When editing Service entity, how can I get service tags names separated by comma in tags text form field?

For example I have 'Math tutor' service with tagList: 'Math', 'Tutor', 'Lessons'. And when I try to edit it, the form should look like:

 | title  |   Math tutor           | <- text field
 | tags   |   Math, Tutor, Lessons | <- text field

Answer 1

You should use DataTransformer: http://symfony.com/doc/current/form/data_transformers.html

This is a small example for a simpler case:

$builder->add('tags', TextType::class);

$builder->get('tags')
        ->addModelTransformer(new CallbackTransformer(
                function ($tagsAsArray) {
                    // transform the array to a string
                    return implode(', ', $tagsAsArray);
                },
                function ($tagsAsString) {
                    // transform the string back to an array
                    return explode(', ', $tagsAsString);
                }
            ))
        ;