.. index:: single: Form; Data transformers How to Use Data Transformers ============================ Data transformers are used to translate the data for a field into a format that can be displayed in a form (and back on submit). They're already used internally for many field types. For example, the :doc:`DateType ` field can be rendered as a ``yyyy-MM-dd``-formatted input text box. Internally, a data transformer converts the starting ``DateTime`` value of the field into the ``yyyy-MM-dd`` string to render the form, and then back into a ``DateTime`` object on submit. .. caution:: When a form field has the ``inherit_data`` option set to ``true``, data transformers are not applied to that field. .. seealso:: If, instead of transforming the representation of a value, you need to map values to a form field and back, you should use a data mapper. Check out :doc:`/form/data_mappers`. .. _simple-example-sanitizing-html-on-user-input: Simple Example: Transforming String Tags from User Input to an Array -------------------------------------------------------------------- Suppose you have a Task form with a tags ``text`` type:: // src/Form/Type/TaskType.php namespace App\Form\Type; use App\Entity\Task; use Symfony\Component\Form\Extension\Core\Type\TextType; use Symfony\Component\Form\FormBuilderInterface; use Symfony\Component\OptionsResolver\OptionsResolver; // ... class TaskType extends AbstractType { public function buildForm(FormBuilderInterface $builder, array $options) { $builder->add('tags', TextType::class); } public function configureOptions(OptionsResolver $resolver) { $resolver->setDefaults([ 'data_class' => Task::class, ]); } // ... } Internally the ``tags`` are stored as an array, but displayed to the user as a simple comma separated string to make them easier to edit. This is a *perfect* time to attach a custom data transformer to the ``tags`` field. The easiest way to do this is with the :class:`Symfony\\Component\\Form\\CallbackTransformer` class:: // src/Form/Type/TaskType.php namespace App\Form\Type; use Symfony\Component\Form\CallbackTransformer; use Symfony\Component\Form\Extension\Core\Type\TextType; use Symfony\Component\Form\FormBuilderInterface; // ... class TaskType extends AbstractType { public function buildForm(FormBuilderInterface $builder, array $options) { $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); } )) ; } // ... } The ``CallbackTransformer`` takes two callback functions as arguments. The first transforms the original value into a format that'll be used to render the field. The second does the reverse: it transforms the submitted value back into the format you'll use in your code. .. tip:: The ``addModelTransformer()`` method accepts *any* object that implements :class:`Symfony\\Component\\Form\\DataTransformerInterface` - so you can create your own classes, instead of putting all the logic in the form (see the next section). You can also add the transformer, right when adding the field by changing the format slightly:: use Symfony\Component\Form\Extension\Core\Type\TextType; $builder->add( $builder ->create('tags', TextType::class) ->addModelTransformer(...) ); Harder Example: Transforming an Issue Number into an Issue Entity ----------------------------------------------------------------- Say you have a many-to-one relation from the Task entity to an Issue entity (i.e. each Task has an optional foreign key to its related Issue). Adding a list box with all possible issues could eventually get *really* long and take a long time to load. Instead, you decide you want to add a text box, where the user can enter the issue number. Start by setting up the text field like normal:: // src/Form/Type/TaskType.php namespace App\Form\Type; use App\Entity\Task; use Symfony\Component\Form\Extension\Core\Type\TextareaType; use Symfony\Component\Form\Extension\Core\Type\TextType; // ... class TaskType extends AbstractType { public function buildForm(FormBuilderInterface $builder, array $options) { $builder ->add('description', TextareaType::class) ->add('issue', TextType::class) ; } public function configureOptions(OptionsResolver $resolver) { $resolver->setDefaults([ 'data_class' => Task::class, ]); } // ... } Good start! But if you stopped here and submitted the form, the Task's ``issue`` property would be a string (e.g. "55"). How can you transform this into an ``Issue`` entity on submit? Creating the Transformer ~~~~~~~~~~~~~~~~~~~~~~~~ You could use the ``CallbackTransformer`` like earlier. But since this is a bit more complex, creating a new transformer class will keep the ``TaskType`` form class simpler. Create an ``IssueToNumberTransformer`` class: it will be responsible for converting to and from the issue number and the ``Issue`` object:: // src/Form/DataTransformer/IssueToNumberTransformer.php namespace App\Form\DataTransformer; use App\Entity\Issue; use Doctrine\ORM\EntityManagerInterface; use Symfony\Component\Form\DataTransformerInterface; use Symfony\Component\Form\Exception\TransformationFailedException; class IssueToNumberTransformer implements DataTransformerInterface { private $entityManager; public function __construct(EntityManagerInterface $entityManager) { $this->entityManager = $entityManager; } /** * Transforms an object (issue) to a string (number). * * @param Issue|null $issue * @return string */ public function transform($issue) { if (null === $issue) { return ''; } return $issue->getId(); } /** * Transforms a string (number) to an object (issue). * * @param string $issueNumber * @return Issue|null * @throws TransformationFailedException if object (issue) is not found. */ public function reverseTransform($issueNumber) { // no issue number? It's optional, so that's ok if (!$issueNumber) { return; } $issue = $this->entityManager ->getRepository(Issue::class) // query for the issue with this id ->find($issueNumber) ; if (null === $issue) { // causes a validation error // this message is not shown to the user // see the invalid_message option throw new TransformationFailedException(sprintf( 'An issue with number "%s" does not exist!', $issueNumber )); } return $issue; } } Just like in the first example, a transformer has two directions. The ``transform()`` method is responsible for converting the data used in your code to a format that can be rendered in your form (e.g. an ``Issue`` object to its ``id``, a string). The ``reverseTransform()`` method does the reverse: it converts the submitted value back into the format you want (e.g. convert the ``id`` back to the ``Issue`` object). To cause a validation error, throw a :class:`Symfony\\Component\\Form\\Exception\\TransformationFailedException`. But the message you pass to this exception won't be shown to the user. You'll set that message with the ``invalid_message`` option (see below). .. note:: When ``null`` is passed to the ``transform()`` method, your transformer should return an equivalent value of the type it is transforming to (e.g. an empty string, 0 for integers or 0.0 for floats). Using the Transformer ~~~~~~~~~~~~~~~~~~~~~ Next, you need to use the ``IssueToNumberTransformer`` object inside of ``TaskType`` and add it to the ``issue`` field. No problem! Add a ``__construct()`` method and type-hint the new class:: // src/Form/Type/TaskType.php namespace App\Form\Type; use App\Form\DataTransformer\IssueToNumberTransformer; use Symfony\Component\Form\Extension\Core\Type\TextareaType; use Symfony\Component\Form\Extension\Core\Type\TextType; // ... class TaskType extends AbstractType { private $transformer; public function __construct(IssueToNumberTransformer $transformer) { $this->transformer = $transformer; } public function buildForm(FormBuilderInterface $builder, array $options) { $builder ->add('description', TextareaType::class) ->add('issue', TextType::class, [ // validation message if the data transformer fails 'invalid_message' => 'That is not a valid issue number', ]); // ... $builder->get('issue') ->addModelTransformer($this->transformer); } // ... } Whenever the transformer throws an exception, the ``invalid_message`` is shown to the user. Instead of showing the same message every time, you can set the end-user error message in the data transformer using the ``setInvalidMessage()`` method. It also allows you to include user values:: // src/Form/DataTransformer/IssueToNumberTransformer.php namespace App\Form\DataTransformer; use Symfony\Component\Form\DataTransformerInterface; use Symfony\Component\Form\Exception\TransformationFailedException; class IssueToNumberTransformer implements DataTransformerInterface { // ... public function reverseTransform($issueNumber) { // ... if (null === $issue) { $privateErrorMessage = sprintf('An issue with number "%s" does not exist!', $issueNumber); $publicErrorMessage = 'The given "{{ value }}" value is not a valid issue number.'; $failure = new TransformationFailedException($privateErrorMessage); $failure->setInvalidMessage($publicErrorMessage, [ '{{ value }}' => $issueNumber, ]); throw $failure; } return $issue; } } That's it! If you're using the :ref:`default services.yaml configuration `, Symfony will automatically know to pass your ``TaskType`` an instance of the ``IssueToNumberTransformer`` thanks to :ref:`autowire ` and :ref:`autoconfigure `. Otherwise, :ref:`register the form class as a service ` and :doc:`tag it ` with the ``form.type`` tag. Now, you can use your ``TaskType``:: // e.g. somewhere in a controller $form = $this->createForm(TaskType::class, $task); // ... Cool, you're done! Your user will be able to enter an issue number into the text field, which will be transformed back into an Issue object. This means that, after a successful submission, the Form component will pass a real ``Issue`` object to ``Task::setIssue()`` instead of the issue number. If the issue isn't found, a form error will be created for that field and its error message can be controlled with the ``invalid_message`` field option. .. caution:: Be careful when adding your transformers. For example, the following is **wrong**, as the transformer would be applied to the entire form, instead of just this field:: // THIS IS WRONG - TRANSFORMER WILL BE APPLIED TO THE ENTIRE FORM // see above example for correct code $builder->add('issue', TextType::class) ->addModelTransformer($transformer); .. _using-transformers-in-a-custom-field-type: Creating a Reusable issue_selector Field ---------------------------------------- In the above example, you applied the transformer to a normal ``text`` field. But if you do this transformation a lot, it might be better to :doc:`create a custom field type `. that does this automatically. First, create the custom field type class:: // src/Form/IssueSelectorType.php namespace App\Form; use App\Form\DataTransformer\IssueToNumberTransformer; use Symfony\Component\Form\AbstractType; use Symfony\Component\Form\Extension\Core\Type\TextType; use Symfony\Component\Form\FormBuilderInterface; use Symfony\Component\OptionsResolver\OptionsResolver; class IssueSelectorType extends AbstractType { private $transformer; public function __construct(IssueToNumberTransformer $transformer) { $this->transformer = $transformer; } public function buildForm(FormBuilderInterface $builder, array $options) { $builder->addModelTransformer($this->transformer); } public function configureOptions(OptionsResolver $resolver) { $resolver->setDefaults([ 'invalid_message' => 'The selected issue does not exist', ]); } public function getParent() { return TextType::class; } } Great! This will act and render like a text field (``getParent()``), but will automatically have the data transformer *and* a nice default value for the ``invalid_message`` option. As long as you're using :ref:`autowire ` and :ref:`autoconfigure `, you can start using the form immediately:: // src/Form/Type/TaskType.php namespace App\Form\Type; use App\Form\DataTransformer\IssueToNumberTransformer; use Symfony\Component\Form\Extension\Core\Type\TextareaType; // ... class TaskType extends AbstractType { public function buildForm(FormBuilderInterface $builder, array $options) { $builder ->add('description', TextareaType::class) ->add('issue', IssueSelectorType::class) ; } // ... } .. tip:: If you're not using ``autowire`` and ``autoconfigure``, see :doc:`/form/create_custom_field_type` for how to configure your new ``IssueSelectorType``. .. _model-and-view-transformers: About Model and View Transformers --------------------------------- In the above example, the transformer was used as a "model" transformer. In fact, there are two different types of transformers and three different types of underlying data. .. image:: /_images/form/data-transformer-types.png :align: center In any form, the three different types of data are: #. **Model data** - This is the data in the format used in your application (e.g. an ``Issue`` object). If you call ``Form::getData()`` or ``Form::setData()``, you're dealing with the "model" data. #. **Norm Data** - This is a normalized version of your data and is commonly the same as your "model" data (though not in our example). It's not commonly used directly. #. **View Data** - This is the format that's used to fill in the form fields themselves. It's also the format in which the user will submit the data. When you call ``Form::submit($data)``, the ``$data`` is in the "view" data format. The two different types of transformers help convert to and from each of these types of data: **Model transformers**: - ``transform()``: "model data" => "norm data" - ``reverseTransform()``: "norm data" => "model data" **View transformers**: - ``transform()``: "norm data" => "view data" - ``reverseTransform()``: "view data" => "norm data" Which transformer you need depends on your situation. To use the view transformer, call ``addViewTransformer()``. So why Use the Model Transformer? --------------------------------- In this example, the field is a ``text`` field, and a text field is always expected to be a simple, scalar format in the "norm" and "view" formats. For this reason, the most appropriate transformer was the "model" transformer (which converts to/from the *norm* format - string issue number - to the *model* format - Issue object). The difference between the transformers is subtle and you should always think about what the "norm" data for a field should really be. For example, the "norm" data for a ``text`` field is a string, but is a ``DateTime`` object for a ``date`` field. .. tip:: As a general rule, the normalized data should contain as much information as possible.