[x] Add a way to add Tags in the form Article.
[x] Link a Tag to an Article if he already exists.
[x] Tags are represented as text with space between other Tags.
[x] Tests dataTransformer.

1. Create an entity Article with those properties :

• title (string)
• author (string)
• content (text)
• createdAt (datetime)

2. Create another entity Tag with a title. Which has a ManyToMany relationship with the Article entity.
3. Create a TagRepository class with the method persistAndFlush, doing basically a persist then a flush of an object "Tag".
4. Make it as a service: create a doctrine.xml file in /Resources/config and declare your repository as a service with factory-service="doctrine.orm.entity_manager" && factory-method="getRepository".
5. Load your doctrine.xml in the Extension file of your bundle (/src/YourBundle/DependencyInjection).
6. Create a ModelTransformer class (TagModelTransformer) which implements the DataTransformerInterface in Form\DataTransformer\.
7. Pass to its constructor the TagRepository
8. Implements the transform and reverseTransform methods for converting an arrayCollection to a simple array and conversely.
9. In reverseTransform method if a tag doesn't exist, persist a new one with ObjectManager. If not, link to Article.
10. Declare the TagModelTransformer as a private service (public="false").
11. Create a ViewTransformer class (TagViewTransformer) which implements the DataTransformerInterface in Form\DataTransformer\.
12. Implements transform and reverseTransform method for converting an array to a string with space and conversely : You can use explode and implode PHP functions.
13. Declare it as a private service.
14. Now time to create a Type for the tag called TagType which implements the method getName() (mandatory, returning a string), and the method buildForm (taking as arguments a FormBuilderInterface && an array of options).
15. Add the TagModelTransformer && TagViewTransformer to the builder.
16. You'll make it a service: you'll need your two DataTransformers, so create 2 private properties that will be initiated in the constructor.
17. Declare it as service: create a form.xml file in /Resources/config and declare your type with the tag form.type (make sure that the alias is the same as the string returned by the getName() method in your type), the two dependancies => your ModelTransformer and ViewTransformer $builder->addViewTransformer($viewTransformer)->addModelTransformer($modelTransformer);
18. Then create a Type for your Article called ArticleType with your new TagType (indicate the alias of your type like ->add('tags', 'tags_selector')).
19. Declare it as a service in the form.xml file.
20. Then create your Controller with actions to show, create, edit, delete articles.
21. Create views accordingly to your actions.
22. Time for tests! Create a directory /Tests/Unit/Form/DataTransformer
23. To test the TagModelTransformerTest:
    • first create a TagModelTransformerTest extending \PHPUnit_Framework_TestCase;
    • implement the setUp() method to initiate the two private properties $repo (a mock of the TagRepository) and $transformer(a real instance of TagModelTransformer taking the repository as argument)
    • create your unit tests to test the transform() and reverseTransform() methods of your ModelTransformer => basically verify that the method converts an arrayCollection to a simple array and conversely.
    • Make sure that your tests cover the case of having an existing tag title and a new tag title!
24. To test the TagViewTransformerTest:
    • first create a TagViewTransformerTest extending \PHPUnit_Framework_TestCase;
    • create your unit tests to test the transform() and reverseTransform() methods of your ViewTransformer => basically verify that the method converts an array to a string with space and conversely.

Et voilà !

Some documentation:

• http://symfony.com/doc/current/cookbook/form/data_transformers.html
• https://speakerdeck.com/webmozart/3-steps-to-symfony2-form-mastery
• https://speakerdeck.com/hhamon/ingenierie-inversee-du-composant-form-de-symfony