feature #37968 [Form] Add new way of mapping data using callback func…

…tions (yceruto)

This PR was merged into the 5.2-dev branch.

Discussion
----------

[Form] Add new way of mapping data using callback functions

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes
| Deprecations? | yes
| Tickets       | Fix #37597 (partially)
| License       | MIT
| Doc PR        | symfony/symfony-docs#14241

Replaces #37614

## What this solves

Objects and Forms have different mechanisms for structuring data. When you build an object model with a lot of business logic it's valuable to use these mechanisms to better collect the data and the behavior that goes with it. Doing so leads to variant schemas; that is, the object model schema and the form schema don't match up.

You still need to transfer data between the two schemas, and this data transfer becomes a complexity in its own right. If the objects know about the form structure, changes in one tend to ripple to the other.

Currently, the Data Mapper layer separates the objects from the form, transfering data between the two and also isolating them from each other. That's fine, but at present the default data mapper has a limitation: _it's very tied to one property path_ (see [`PropertyPathMapper`](https://github.com/symfony/symfony/blob/5.1/src/Symfony/Component/Form/Extension/Core/DataMapper/PropertyPathMapper.php)).

That said, you'll have to write your own data mapper in the following situations:
 * When the property path differs for reading and writing
 * When several form fields are mapped to a single method
 * When you need to read data based on the model's state
 * When the mapping of the model depends on the submitted form data
 * ...

Also, when we create a new data mapper, we usually forget about checking the status of the given data and forms. Whether the data is empty or not; throw an exception if the given data is not an object/array and whether the form field is submitted/synchronized/disabled or not. Not doing that could lead to unwanted behavior.

## What this proposes

Create a new way to write and read values to/from an object/array using callback functions. This feature would be tied to each form field and would also mean a new way of mapping data, but a very convenient one, in which it won't be necessary to define a new data mapper and take into account all what it would imply when you only need to map one field in a different manner or perhaps in only one direction (writing or reading the value).

This PR adds two new options for each form type: `getter` and `setter`, allowed to be `null` or `callable`:
```php
$builder->add('name', TextType::class, [
    'getter' => function (Person $person, FormInterface $form): string {
        return $person->firstName().' '.$person->lastName();
    },
    'setter' => function (Person &$person, ?string $name, FormInterface $form): void {
        $person->rename($name);
    },
]);
```
This would give us the same possibilities as data mappers, but within the form field scope, where:
 * `$person` is the view data, basically the underlying data to the form.
 * `$form` is the current child form that is being mapped.
 * `$name` is the submitted data that belongs to that field.

These two callbacks will be executed following the same rules as for property paths before read and write any value (e.i. early return if empty data, skip mapping if the form field is not mapped or it's disabled, etc).

## What this also proposes

I based the implementation on solving this problem first:

> #37614 (comment)
> [...] the property_path option defines the rules on how it's accessed. From there, the actual way it is accessed (direct property access, accessors, reflection, whatever) are hidden from view. All that matters is the property path (which is deduced from the name if not explicitly set). [...]

So splitting the default data mapper `PropertyPathMapper` into two artifacts: "[DataMapper](https://github.com/yceruto/symfony/blob/data_accessor/src/Symfony/Component/Form/Extension/Core/DataMapper/DataMapper.php)" and "[DataAccessor](https://github.com/yceruto/symfony/blob/data_accessor/src/Symfony/Component/Form/DataAccessorInterface.php)" would allow us adding multiple data accessors along the way (the code that varies in this case) without having to reinvent the wheel over and over again (the data mapper code).

You can also think about a new `ReflectionAccessor` for instance? or use this `CallbackAccessor` to map your form partially from an external API? yes, you could do it :)

Here is a view of the proposed changes:

![data_accessor](https://user-images.githubusercontent.com/2028198/91452859-16bf8f00-e84d-11ea-8564-d497c2f73730.png)

Where "DataMapper" will take care of common checks, iterates the given child forms, manages the form data and all what is needed for mapping a standard form, whereas "DataAccessor" will take care of how to read and write values to/from the underlying object or array.

## BC

The `PropertyPathMapper` is being deprecated in favor of `DataMapper` class, which uses the `PropertyPathAccessor` by default.

Although `DataMapper` is now the default for each compound form, the behavior must remains the same (tests prove it). So that if `getter` or `setter` option is null (they're by default) the `CallbackAccessor` will falls back to `PropertyPathAccessor` either for reading or writing values.

---

Sorry for the long description, but I think that sometimes it is necessary for too complex issues and big changes. Besides, now you know a little more about what these changes is about.

/cc @xabbuh as creator of [rich-model-forms-bundle](https://github.com/sensiolabs-de/rich-model-forms-bundle) and @alcaeus as you had worked on this issue.

WDYT?

Commits
-------

878effa add new way of mapping data using callback functions

UPGRADE-5.2.md

@@ -16,6 +16,28 @@ FrameworkBundle
    used to be added by default to the seed, which is not the case anymore. This allows sharing caches between
    apps or different environments.
 
+Form
+----
+
+ * Deprecated `PropertyPathMapper` in favor of `DataMapper` and `PropertyPathAccessor`.
+
+ Before:
+
+ ```php
+ use Symfony\Component\Form\Extension\Core\DataMapper\PropertyPathMapper;
+
+ $builder->setDataMapper(new PropertyPathMapper());
+ ```
+
+ After:
+
+ ```php
+ use Symfony\Component\Form\Extension\Core\DataAccessor\PropertyPathAccessor;
+ use Symfony\Component\Form\Extension\Core\DataMapper\DataMapper;
+
+ $builder->setDataMapper(new DataMapper(new PropertyPathAccessor()));
+ ```
+
 Lock
 ----
 

UPGRADE-6.0.md

@@ -48,6 +48,7 @@ Form
  * Added argument `callable|null $filter` to `ChoiceListFactoryInterface::createListFromChoices()` and `createListFromLoader()`.
  * The `Symfony\Component\Form\Extension\Validator\Util\ServerParams` class has been removed, use its parent `Symfony\Component\Form\Util\ServerParams` instead.
  * The `NumberToLocalizedStringTransformer::ROUND_*` constants have been removed, use `\NumberFormatter::ROUND_*` instead.
+ * Removed `PropertyPathMapper` in favor of `DataMapper` and `PropertyPathAccessor`.
 
 FrameworkBundle
 ---------------

src/Symfony/Component/Form/CHANGELOG.md

@@ -5,6 +5,8 @@ CHANGELOG
 -----
 
  * Added support for using the `{{ label }}` placeholder in constraint messages, which is replaced in the `ViolationMapper` by the corresponding field form label.
+ * Added `DataMapper`, `ChainAccessor`, `PropertyPathAccessor` and `CallbackAccessor` with new callable `getter` and `setter` options for each form type
+ * Deprecated `PropertyPathMapper` in favor of `DataMapper` and `PropertyPathAccessor`
 
 5.1.0
 -----

src/Symfony/Component/Form/DataAccessorInterface.php

@@ -0,0 +1,69 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Form;
+
+/**
+ * Writes and reads values to/from an object or array bound to a form.
+ *
+ * @author Yonel Ceruto <yonelceruto@gmail.com>
+ */
+interface DataAccessorInterface
+{
+    /**
+     * Returns the value at the end of the property of the object graph.
+     *
+     * @param object|array  $viewData The view data of the compound form
+     * @param FormInterface $form     The {@link FormInterface()} instance to check
+     *
+     * @return mixed The value at the end of the property
+     *
+     * @throws Exception\AccessException If unable to read from the given form data
+     */
+    public function getValue($viewData, FormInterface $form);
+
+    /**
+     * Sets the value at the end of the property of the object graph.
+     *
+     * @param object|array  $viewData The view data of the compound form
+     * @param mixed         $value    The value to set at the end of the object graph
+     * @param FormInterface $form     The {@link FormInterface()} instance to check
+     *
+     * @throws Exception\AccessException If unable to write the given value
+     */
+    public function setValue(&$viewData, $value, FormInterface $form): void;
+
+    /**
+     * Returns whether a value can be read from an object graph.
+     *
+     * Whenever this method returns true, {@link getValue()} is guaranteed not
+     * to throw an exception when called with the same arguments.
+     *
+     * @param object|array  $viewData The view data of the compound form
+     * @param FormInterface $form     The {@link FormInterface()} instance to check
+     *
+     * @return bool Whether the value can be read
+     */
+    public function isReadable($viewData, FormInterface $form): bool;
+
+    /**
+     * Returns whether a value can be written at a given object graph.
+     *
+     * Whenever this method returns true, {@link setValue()} is guaranteed not
+     * to throw an exception when called with the same arguments.
+     *
+     * @param object|array  $viewData The view data of the compound form
+     * @param FormInterface $form     The {@link FormInterface()} instance to check
+     *
+     * @return bool Whether the value can be set
+     */
+    public function isWritable($viewData, FormInterface $form): bool;
+}

src/Symfony/Component/Form/Exception/AccessException.php

@@ -0,0 +1,16 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Form\Exception;
+
+class AccessException extends RuntimeException
+{
+}

src/Symfony/Component/Form/Extension/Core/DataAccessor/CallbackAccessor.php

@@ -0,0 +1,64 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Form\Extension\Core\DataAccessor;
+
+use Symfony\Component\Form\DataAccessorInterface;
+use Symfony\Component\Form\Exception\AccessException;
+use Symfony\Component\Form\FormInterface;
+
+/**
+ * Writes and reads values to/from an object or array using callback functions.
+ *
+ * @author Yonel Ceruto <yonelceruto@gmail.com>
+ */
+class CallbackAccessor implements DataAccessorInterface
+{
+    /**
+     * {@inheritdoc}
+     */
+    public function getValue($data, FormInterface $form)
+    {
+        if (null === $getter = $form->getConfig()->getOption('getter')) {
+            throw new AccessException('Unable to read from the given form data as no getter is defined.');
+        }
+
+        return ($getter)($data, $form);
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function setValue(&$data, $value, FormInterface $form): void
+    {
+        if (null === $setter = $form->getConfig()->getOption('setter')) {
+            throw new AccessException('Unable to write the given value as no setter is defined.');
+        }
+
+        ($setter)($data, $form->getData(), $form);
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function isReadable($data, FormInterface $form): bool
+    {
+        return null !== $form->getConfig()->getOption('getter');
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function isWritable($data, FormInterface $form): bool
+    {
+        return null !== $form->getConfig()->getOption('setter');
+    }
+}

src/Symfony/Component/Form/Extension/Core/DataAccessor/ChainAccessor.php

@@ -0,0 +1,90 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Form\Extension\Core\DataAccessor;
+
+use Symfony\Component\Form\DataAccessorInterface;
+use Symfony\Component\Form\Exception\AccessException;
+use Symfony\Component\Form\FormInterface;
+
+/**
+ * @author Yonel Ceruto <yonelceruto@gmail.com>
+ */
+class ChainAccessor implements DataAccessorInterface
+{
+    private $accessors;
+
+    /**
+     * @param DataAccessorInterface[]|iterable $accessors
+     */
+    public function __construct(iterable $accessors)
+    {
+        $this->accessors = $accessors;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getValue($data, FormInterface $form)
+    {
+        foreach ($this->accessors as $accessor) {
+            if ($accessor->isReadable($data, $form)) {
+                return $accessor->getValue($data, $form);
+            }
+        }
+
+        throw new AccessException('Unable to read from the given form data as no accessor in the chain is able to read the data.');
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function setValue(&$data, $value, FormInterface $form): void
+    {
+        foreach ($this->accessors as $accessor) {
+            if ($accessor->isWritable($data, $form)) {
+                $accessor->setValue($data, $value, $form);
+
+                return;
+            }
+        }
+
+        throw new AccessException('Unable to write the given value as no accessor in the chain is able to set the data.');
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function isReadable($data, FormInterface $form): bool
+    {
+        foreach ($this->accessors as $accessor) {
+            if ($accessor->isReadable($data, $form)) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function isWritable($data, FormInterface $form): bool
+    {
+        foreach ($this->accessors as $accessor) {
+            if ($accessor->isWritable($data, $form)) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+}

src/Symfony/Component/Form/Extension/Core/DataAccessor/PropertyPathAccessor.php

@@ -0,0 +1,102 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Form\Extension\Core\DataAccessor;
+
+use Symfony\Component\Form\DataAccessorInterface;
+use Symfony\Component\Form\Exception\AccessException;
+use Symfony\Component\Form\FormInterface;
+use Symfony\Component\PropertyAccess\Exception\AccessException as PropertyAccessException;
+use Symfony\Component\PropertyAccess\Exception\UninitializedPropertyException;
+use Symfony\Component\PropertyAccess\PropertyAccess;
+use Symfony\Component\PropertyAccess\PropertyAccessorInterface;
+
+/**
+ * Writes and reads values to/from an object or array using property path.
+ *
+ * @author Yonel Ceruto <yonelceruto@gmail.com>
+ * @author Bernhard Schussek <bschussek@gmail.com>
+ */
+class PropertyPathAccessor implements DataAccessorInterface
+{
+    private $propertyAccessor;
+
+    public function __construct(PropertyAccessorInterface $propertyAccessor = null)
+    {
+        $this->propertyAccessor = $propertyAccessor ?? PropertyAccess::createPropertyAccessor();
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getValue($data, FormInterface $form)
+    {
+        if (null === $propertyPath = $form->getPropertyPath()) {
+            throw new AccessException('Unable to read from the given form data as no property path is defined.');
+        }
+
+        return $this->getPropertyValue($data, $propertyPath);
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function setValue(&$data, $propertyValue, FormInterface $form): void
+    {
+        if (null === $propertyPath = $form->getPropertyPath()) {
+            throw new AccessException('Unable to write the given value as no property path is defined.');
+        }
+
+        // If the field is of type DateTimeInterface and the data is the same skip the update to
+        // keep the original object hash
+        if ($propertyValue instanceof \DateTimeInterface && $propertyValue == $this->getPropertyValue($data, $propertyPath)) {
+            return;
+        }
+
+        // If the data is identical to the value in $data, we are
+        // dealing with a reference
+        if (!\is_object($data) || !$form->getConfig()->getByReference() || $propertyValue !== $this->getPropertyValue($data, $propertyPath)) {
+            $this->propertyAccessor->setValue($data, $propertyPath, $propertyValue);
+        }
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function isReadable($data, FormInterface $form): bool
+    {
+        return null !== $form->getPropertyPath();
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function isWritable($data, FormInterface $form): bool
+    {
+        return null !== $form->getPropertyPath();
+    }
+
+    private function getPropertyValue($data, $propertyPath)
+    {
+        try {
+            return $this->propertyAccessor->getValue($data, $propertyPath);
+        } catch (PropertyAccessException $e) {
+            if (!$e instanceof UninitializedPropertyException
+                // For versions without UninitializedPropertyException check the exception message
+                && (class_exists(UninitializedPropertyException::class) || false === strpos($e->getMessage(), 'You should initialize it'))
+            ) {
+                throw $e;
+            }
+
+            return null;
+        }
+    }
+}