Updated the documentation for the simplified Callback constraint

Author: webmozart

reference/constraints/Callback.rst

@@ -1,7 +1,12 @@
 Callback
 ========
 
-The purpose of the Callback assertion is to let you create completely custom
+.. versionadded:: 2.4
+    The ``Callback`` constraint was simplified in Symfony 2.4. For usage
+    examples with older Symfony versions, see the corresponding versions of this
+    documentation page.
+
+The purpose of the Callback constraint is to create completely custom
 validation rules and to assign any validation errors to specific fields on
 your object. If you're using validation with forms, this means that you can
 make these custom errors display next to a specific field, instead of simply
@@ -20,15 +25,15 @@ can do anything, including creating and assigning validation errors.
 +----------------+------------------------------------------------------------------------+
 | Applies to     | :ref:`class<validation-class-target>`                                  |
 +----------------+------------------------------------------------------------------------+
-| Options        | - `methods`_                                                           |
+| Options        | - `callback`_                                                          |
 +----------------+------------------------------------------------------------------------+
 | Class          | :class:`Symfony\\Component\\Validator\\Constraints\\Callback`          |
 +----------------+------------------------------------------------------------------------+
 | Validator      | :class:`Symfony\\Component\\Validator\\Constraints\\CallbackValidator` |
 +----------------+------------------------------------------------------------------------+
 
-Setup
------
+Configuration
+-------------
 
 .. configuration-block::
 
@@ -37,21 +42,25 @@ Setup
         # src/Acme/BlogBundle/Resources/config/validation.yml
         Acme\BlogBundle\Entity\Author:
             constraints:
-                - Callback:
-                    methods:   [isAuthorValid]
+                - Callback: validate
 
     .. code-block:: php-annotations
 
         // src/Acme/BlogBundle/Entity/Author.php
         namespace Acme\BlogBundle\Entity;
 
         use Symfony\Component\Validator\Constraints as Assert;
+        use Symfony\Component\Validator\ExecutionContextInterface;
 
-        /**
-         * @Assert\Callback(methods={"isAuthorValid"})
-         */
         class Author
         {
+            /**
+             * @Assert\Callback
+             */
+            public function validate(ExecutionContextInterface $context)
+            {
+                // ...
+            }
         }
 
     .. code-block:: xml
@@ -63,11 +72,7 @@ Setup
             xsi:schemaLocation="http://symfony.com/schema/dic/constraint-mapping http://symfony.com/schema/dic/constraint-mapping/constraint-mapping-1.0.xsd">
 
             <class name="Acme\BlogBundle\Entity\Author">
-                <constraint name="Callback">
-                    <option name="methods">
-                        <value>isAuthorValid</value>
-                    </option>
-                </constraint>
+                <constraint name="Callback">validate</constraint>
             </class>
         </constraint-mapping>
 
@@ -83,9 +88,7 @@ Setup
         {
             public static function loadValidatorMetadata(ClassMetadata $metadata)
             {
-                $metadata->addConstraint(new Assert\Callback(array(
-                    'methods' => array('isAuthorValid'),
-                )));
+                $metadata->addConstraint(new Assert\Callback('validate'));
             }
         }
 
@@ -98,133 +101,171 @@ those errors should be attributed::
 
     // ...
     use Symfony\Component\Validator\ExecutionContextInterface;
-    
+
     class Author
     {
         // ...
         private $firstName;
-    
-        public function isAuthorValid(ExecutionContextInterface $context)
+
+        public function validate(ExecutionContextInterface $context)
         {
             // somehow you have an array of "fake names"
-            $fakeNames = array();
-        
+            $fakeNames = array(/* ... */);
+
             // check if the name is actually a fake name
             if (in_array($this->getFirstName(), $fakeNames)) {
-                $context->addViolationAt('firstname', 'This name sounds totally fake!', array(), null);
+                $context->addViolationAt('firstName', 'This name sounds totally fake!', array(), null);
             }
         }
     }
 
-Options
--------
+Static Callbacks
+----------------
 
-methods
-~~~~~~~
+You can also use the constraint with static methods. Since static methods don't
+have access to the object instance, they receive the object as first argument::
 
-**type**: ``array`` **default**: ``array()`` [:ref:`default option<validation-default-option>`]
+    public static function validate($object, ExecutionContextInterface $context)
+    {
+        // somehow you have an array of "fake names"
+        $fakeNames = array(/* ... */);
 
-This is an array of the methods that should be executed during the validation
-process. Each method can be one of the following formats:
+        // check if the name is actually a fake name
+        if (in_array($object->getFirstName(), $fakeNames)) {
+            $context->addViolationAt('firstName', 'This name sounds totally fake!', array(), null);
+        }
+    }
 
-1) **String method name**
+External Callbacks and Closures
+-------------------------------
 
-    If the name of a method is a simple string (e.g. ``isAuthorValid``), that
-    method will be called on the same object that's being validated and the
-    ``ExecutionContextInterface`` will be the only argument (see the above example).
+If you want to execute a static callback method that is not located in the class
+of the validated object, you can configure the constraint to invoke an array
+callable as supported by PHP's :phpfunction:`call_user_func` function. Suppose
+your validation function is `Vendor\Package\Validator::validate()`::
 
-2) **Static array callback**
+    namespace Vendor\Package;
 
-    Each method can also be specified as a standard array callback:
+    use Symfony\Component\Validator\ExecutionContextInterface;
 
-    .. configuration-block::
+    class Validator
+    {
+        public function validate($object, ExecutionContextInterface $context)
+        {
+            // ...
+        }
+    }
 
-        .. code-block:: yaml
+You can then use the following configuration to invoke this validator::
 
-            # src/Acme/BlogBundle/Resources/config/validation.yml
-            Acme\BlogBundle\Entity\Author:
-                constraints:
-                    - Callback:
-                        methods:
-                            -    [Acme\BlogBundle\MyStaticValidatorClass, isAuthorValid]
+.. configuration-block::
 
-        .. code-block:: php-annotations
+    .. code-block:: yaml
 
-            // src/Acme/BlogBundle/Entity/Author.php
-            use Symfony\Component\Validator\Constraints as Assert;
+        # src/Acme/BlogBundle/Resources/config/validation.yml
+        Acme\BlogBundle\Entity\Author:
+            constraints:
+                - Callback: [Vendor\Package\Validator, validate]
 
-            /**
-             * @Assert\Callback(methods={
-             *     { "Acme\BlogBundle\MyStaticValidatorClass", "isAuthorValid"}
-             * })
-             */
-            class Author
-            {
-            }
+    .. code-block:: php-annotations
 
-        .. code-block:: xml
+        // src/Acme/BlogBundle/Entity/Author.php
+        namespace Acme\BlogBundle\Entity;
 
-            <!-- src/Acme/BlogBundle/Resources/config/validation.xml -->
-            <?xml version="1.0" encoding="UTF-8" ?>
-            <constraint-mapping xmlns="http://symfony.com/schema/dic/constraint-mapping"
-                xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-                xsi:schemaLocation="http://symfony.com/schema/dic/constraint-mapping http://symfony.com/schema/dic/constraint-mapping/constraint-mapping-1.0.xsd">
+        use Symfony\Component\Validator\Constraints as Assert;
+        use Symfony\Component\Validator\ExecutionContextInterface;
 
-                <class name="Acme\BlogBundle\Entity\Author">
-                    <constraint name="Callback">
-                        <option name="methods">
-                            <value>
-                                <value>Acme\BlogBundle\MyStaticValidatorClass</value>
-                                <value>isAuthorValid</value>
-                            </value>
-                        </option>
-                    </constraint>
-                </class>
-            </constraint-mapping>
+        /**
+         * @Assert\Callback({"Vendor\Package\Validator", "validate"})
+         */
+        class Author
+        {
+        }
 
-        .. code-block:: php
+    .. code-block:: xml
 
-            // src/Acme/BlogBundle/Entity/Author.php
+        <!-- src/Acme/BlogBundle/Resources/config/validation.xml -->
+        <?xml version="1.0" encoding="UTF-8" ?>
+        <constraint-mapping xmlns="http://symfony.com/schema/dic/constraint-mapping"
+            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+            xsi:schemaLocation="http://symfony.com/schema/dic/constraint-mapping http://symfony.com/schema/dic/constraint-mapping/constraint-mapping-1.0.xsd">
+
+            <class name="Acme\BlogBundle\Entity\Author">
+                <constraint name="Callback">
+                    <value>Vendor\Package\Validator</value>
+                    <value>validate</value>
+                </constraint>
+            </class>
+        </constraint-mapping>
 
-            use Symfony\Component\Validator\Mapping\ClassMetadata;
-            use Symfony\Component\Validator\Constraints\Callback;
+    .. code-block:: php
 
-            class Author
+        // src/Acme/BlogBundle/Entity/Author.php
+        namespace Acme\BlogBundle\Entity;
+
+        use Symfony\Component\Validator\Mapping\ClassMetadata;
+        use Symfony\Component\Validator\Constraints as Assert;
+
+        class Author
+        {
+            public static function loadValidatorMetadata(ClassMetadata $metadata)
             {
-                public $name;
-
-                public static function loadValidatorMetadata(ClassMetadata $metadata)
-                {
-                    $metadata->addConstraint(new Callback(array(
-                        'methods' => array(
-                            array('Acme\BlogBundle\MyStaticValidatorClass', 'isAuthorValid'),
-                        ),
-                    )));
-                }
+                $metadata->addConstraint(new Assert\Callback(array(
+                    'Vendor\Package\Validator',
+                    'validate'
+                )));
             }
+        }
 
-    In this case, the static method ``isAuthorValid`` will be called on the
-    ``Acme\BlogBundle\MyStaticValidatorClass`` class. It's passed both the original
-    object being validated (e.g. ``Author``) as well as the ``ExecutionContextInterface``::
+.. note::
 
-        namespace Acme\BlogBundle;
-    
-        use Symfony\Component\Validator\ExecutionContextInterface;
-        use Acme\BlogBundle\Entity\Author;
-    
-        class MyStaticValidatorClass
+    The Callback constraint does *not* support global callback functions or
+    It is *not* possible to specify a global function or a :term:`service`
+    method as callback. To validate using a service, you should
+    :doc:`create a custom validation constraint</cookbook/validation/custom_constraint>`
+    and add that new constraint to your class.
+
+When configuring the constraint via PHP, you can also pass a closure to the
+constructor of the Callback constraint::
+
+    // src/Acme/BlogBundle/Entity/Author.php
+    namespace Acme\BlogBundle\Entity;
+
+    use Symfony\Component\Validator\Mapping\ClassMetadata;
+    use Symfony\Component\Validator\Constraints as Assert;
+
+    class Author
+    {
+        public static function loadValidatorMetadata(ClassMetadata $metadata)
         {
-            public static function isAuthorValid(Author $author, ExecutionContextInterface $context)
-            {
+            $callback = function ($object, ExecutionContextInterface $context) {
                 // ...
-            }
+            };
+
+            $metadata->addConstraint(new Assert\Callback($callback));
         }
+    }
+
+Options
+-------
+
+callback
+~~~~~~~~
+
+**type**: ``string``, ``array`` or ``Closure`` [:ref:`default option<validation-default-option>`]
+
+The callback option accepts three different formats for specifying the
+callback method:
+
+* A **string** containing the name of a concrete or static method.
+
+* An array callable with the format ``array('<Class>', '<method>')``.
+
+* A closure.
 
-    .. tip::
+Concrete callbacks receive an :class:`Symfony\\Component\\Validator\\ExecutionContextInterface`
+instance as only argument.
 
-        If you specify your ``Callback`` constraint via PHP, then you also have
-        the option to make your callback either a PHP closure or a non-static
-        callback. It is *not* currently possible, however, to specify a :term:`service`
-        as a constraint. To validate using a service, you should
-        :doc:`create a custom validation constraint</cookbook/validation/custom_constraint>`
-        and add that new constraint to your class.
+Static or closure callbacks receive the validated object as first argument
+and the :class:`Symfony\\Component\\Validator\\ExecutionContextInterface`
+instance as second argument.