Version 6 supported

Extension

An Extension allows for adding additional functionality to a class or modifying existing functionality without the hassle of creating a subclass. Developers can add Extensions to any PHP class that has the Extensible trait applied within core, modules or even their own code to make it more reusable.

Extensions are defined as subclasses of the Extension class. Typically, subclasses of the Extension class are used for extending a DataObject subclass.

For performance reasons a few classes are excluded from receiving extensions, including ModelData and RequestHandler. You can still apply extensions to descendants of these classes.

// app/src/Extension/MyMemberExtension.php
namespace App\Extension;

use SilverStripe\Core\Extension;

class MyMemberExtension extends Extension
{
    private static $db = [
        'DateOfBirth' => 'DBDatetime',
    ];

    public function getGreeting()
    {
        // $this->owner refers to the instance being extended - in this case a `Member` record.
        return "Hi {$this->owner->Name}";
    }
}

Convention is for extension class names to end in Extension. This isn't a requirement but makes it clearer

After this class has been created, it does not yet apply it to any object. We need to tell Silverstripe CMS what classes we want to add the MyMemberExtension to. To activate this extension, add the following via the Configuration API.

# app/_config/extensions.yml
SilverStripe\Security\Member:
  extensions:
    - App\Extension\MyMemberExtension

Alternatively, we can add extensions through PHP code (in the _config.php file).

use App\Extension\MyMemberExtension;
use SilverStripe\Security\Member;

Member::add_extension(MyMemberExtension::class);

This class now defines a MyMemberExtension that applies to all Member instances on the website. It will have transformed the original Member class in two ways:

  • Added a new DBDatetime database field for the user's date of birth, and;
  • Added a public getGreeting method to output Hi <User>

From within the extension we can add more functions, database fields, relations or other properties and have them added to the underlying DataObject just as if they were added to the original Member class but without the need to edit that file directly.

Owner

In your Extension class you can only refer to the source object through the owner property on the class as $this will refer to your Extension instance.

// app/src/Extension/MyMemberExtension.php
namespace App\Extension;

use SilverStripe\Core\Extension;

class MyMemberExtension extends Extension
{
    public function updateFoo($foo)
    {
        // outputs the class name of the object being extended
        var_dump(get_class($this->owner));
    }
}

Adding configuration properties

Extension classes can add to configuration properties for the classes they extend. Any configuration property declared in an extension can be accessed both from the context of the extension class itself as well as from the context of the class being extended.

namespace App\Data;

use SilverStripe\Model\ModelData;

class MyDataClass extends ModelData
{
    private static array $my_configuration_property = [
        'key1' => 'value1',
        'key2' => 'value2',
    ];
}
namespace App\Extension;

use SilverStripe\Core\Extension;

class MyDataClassConfigExtension extends Extension
{
    private static array $my_configuration_property = [
        'key1' => 'not overridden',
        'key3' => 'value3',
    ];

    private static bool $new_config_property = true;
}
App\Data\MyDataClass:
  extensions:
    - App\Extension\MyDataClassConfigExtension

With the above code, we end up with the following resultant configuration:

App\Data\MyDataClass:
  my_configuration_property:
    key1: 'value1'
    key2: 'value2'
    key3: 'value3'
  new_config_property: true
  extensions:
    - App\Extension\MyDataClassConfigExtension

App\Extension\MyDataClassConfigExtension:
  my_configuration_property:
    key1: 'not overridden'
    key3: 'value3'
  new_config_property: true

Note that the value for key1 in the my_configuration_property array was not overridden by the extension class. Configuration declared in an extension class is merged into the base class as a lower priority than the base class itself. Where there is any collision between the configuration declared on the base class and on the extension class, the base class configuration is used.

If you need to override values, you should do so using the yml configuration API.

App\Data\MyDataClass:
  my_configuration_property:
    key1: 'is overridden'

See Configuration API for more information about configuration properties.

Adding database fields

Extra database fields can be added with a extension in the same manner as if they were placed on the DataObject class they're applied to. These will be added to the table of the base object.

Because $db, $has_one, etc are ultimately just configuration properties, they work the same way as described in adding configuration properties above.

// app/src/extension/MyMemberExtension.php
namespace App\Extension;

use SilverStripe\Assets\Image;
use SilverStripe\Core\Extension;

class MyMemberExtension extends Extension
{
    private static $db = [
        'Position' => 'Varchar',
    ];

    private static $has_one = [
        'Image' => Image::class,
    ];
}
<%-- app/templates/Page.ss --%>
$CurrentMember.Position
$CurrentMember.Image

Adding methods

Public methods that have a unique name will be called as part of the __call method on the extended object. In the first example on this page we added a getGreeting method which is unique to our extension.

<%-- app/templates/Page.ss --%>
<p>$CurrentMember.Greeting</p>
<%-- "Hi Sam" --%>
// app/src/Extension/MyMemberExtension.php
namespace App\Extension;

$member = Security::getCurrentUser();
// "Hi Sam"
echo $member->getGreeting();

Note that protected, private, and static methods are not accessible from the extended object/class.

Modifying existing methods

If the Extension needs to modify an existing method it's a little trickier. It requires that the method you want to customise has provided an Extension Hook in the place where you want to modify the data. An Extension Hook is done through the extend() or invokeWithExtensions() method of the Extensible trait.

// silverstripe/framework/src/Security/Member.php
namespace SilverStripe\Security;

use SilverStripe\ORM\DataObject;
// ...

class Member extends DataObject
{
    // ...
    public function getValidator()
    {
        // ...
        $this->extend('updateValidator', $validator);
        // ...
    }
    // ...
}

Extension Hooks can be located anywhere in the method and provide a point for any Extension instances to modify the variables at that given point. In this case, the core function getValidator on the Member class provides an updateValidator hook for developers to modify the core method. The MyMemberExtension would modify the core member's validator by defining the updateValidator method.

// app/src/Extension/MyMemberExtension.php
namespace App\Extension;

use SilverStripe\Core\Extension;

class MyMemberExtension extends Extension
{
    protected function updateValidator($validator)
    {
        // we want to make date of birth required for each member
        $validator->addRequiredField('DateOfBirth');
    }
}

In this case the $validator argument can be modified directly, as it is an object. To modify literals, you will need to explicitly pass by reference.

Another common example of when you will want to modify a method is to update the default CMS fields for an object in an extension. The CMS provides a updateCMSFields Extension Hook to tie into.

namespace App\Extension;

use SilverStripe\AssetAdmin\Forms\UploadField;
use SilverStripe\Core\Extension;
use SilverStripe\Forms\FieldList;
use SilverStripe\Forms\TextField;

class MyMemberExtension extends Extension
{
    private static $db = [
        'Position' => 'Varchar',
    ];

    private static $has_one = [
        'Image' => 'Image',
    ];

    protected function updateCMSFields(FieldList $fields)
    {
        $fields->push(TextField::create('Position'));
        $fields->push($upload = UploadField::create('Image', 'Profile Image'));
        $upload->setAllowedFileCategories('image/supported');
    }
}

If you're providing a module or working on code that may need to be extended by other code, it should provide a hook which allows an Extension to modify the results.

namespace App\Model;

use SilverStripe\ORM\DataObject;

class MyModel extends DataObject
{
    // ...

    public function getFoo()
    {
        $foo = '';

        $this->extend('updateFoo', $foo);

        return $foo;
    }
}

The convention for extension hooks is to provide an update{$Function} hook at the end before you return the result. If you need to provide extension hooks at the beginning of the method use before{$Function}.

Checking to see if an object has an extension

To see what extensions are currently enabled on an object, use the getExtensionInstances() and hasExtension() methods of the Extensible trait.

$member = Security::getCurrentUser();

if ($member->hasExtension(MyCustomMemberExtension::class)) {
    // ...
}

foreach ($member->getExtensionInstances() as $extension) {
    // ...
};

Extension injection points

Extensible has two additional methods, beforeExtending and afterExtending, each of which takes a method name and a callback to be executed immediately before and after extend() is called on extensions.

This is useful in many cases where working with modules such as tractorcow/silverstripe-fluent which operate on DataObject fields that must exist in the FieldList at the time that $this->extend('UpdateCMSFields') is called.

Please note that each callback is only ever called once, and then cleared, so multiple extensions to the same function require that a callback is registered each time, if necessary.

Example: A class that wants to control default values during object initialization. The code needs to assign a value if not specified in self::$defaults, but before extensions have been called:

namespace App\Model;

use SilverStripe\ORM\DataObject;

class MyModel extends DataObject
{
    private static $db = [
        'MyField' => 'Text',
    ];

    public function __construct()
    {
        $this->beforeExtending('onAfterPopulateDefaults', function () {
            if (empty($this->MyField)) {
                $this->MyField = 'Value we want as a default if not specified in $defaults, but set before extensions';
            }
        });

        parent::__construct();
    }
}

Example 2: User code can intervene in the process of extending CMS fields.

This method is preferred to disabling, enabling, and calling field extensions manually.

namespace App\Model;

use SilverStripe\Forms\FieldList;
use SilverStripe\Forms\TextField;
use SilverStripe\ORM\DataObject;

class MyModel extends DataObject
{
    // ...

    public function getCMSFields()
    {
        $this->beforeUpdateCMSFields(function (FieldList $fields) {
            // Include field which must be present when updateCMSFields is called on extensions
            $fields->addFieldToTab('Root.Main', TextField::create('Detail', 'Details', null, 255));
        });

        $fields = parent::getCMSFields();
        // ... additional fields here
        return $fields;
    }
}

Extending extensions

Extension classes can be overridden using the Injector, if you want to modify the way that an extension in one of your modules works:

SilverStripe\Core\Injector\Injector:
  Company\Vendor\SomeExtension:
    class: App\Extension\CustomisedSomeExtension
// app/src/Extension/CustomisedSomeExtension.php
namespace App\Extension;

use Company\Vendor\SomeExtension;

class CustomisedSomeExtension extends SomeExtension
{
    public function someMethod()
    {
        $result = parent::someMethod();
        // modify result;
        return $result;
    }
}

Please note that overriding the extension like this should be done in YAML configuration using the injector only. It is not recommended to use Config::modify()->set() to adjust the implementation class name of an extension after the configuration manifest has been loaded, which may not work consistently due to the "extra methods" cache having already been populated.

Related documentation

API documentation

Edit on Github