Extension and DataExtension
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 either DataExtension for extending a DataObject subclass or the Extension class for non DataObject subclasses (such as Controller)
For performance reasons a few classes are excluded from receiving extensions, including ViewableData
and RequestHandler. You can still apply extensions to descendants of these classes.
// app/src/Extension/MyMemberExtension.php
namespace App\Extension;
use SilverStripe\ORM\DataExtension;
class MyMemberExtension extends DataExtension
{
private static $db = [
'DateOfBirth' => 'DBDatetime',
];
public function getGreeting()
{
// $this->owner refers to the original instance. In this case a `Member`.
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 too. To activate this extension, add the following via the Configuration API.
# app/_config/extensions.yml
SilverStripe\Security\Member:
extensions:
- App\Extension\MyMemberExtensionAlternatively, 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 for the users date of birth, and;
- Added a
getGreetingmethod to outputHi <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.
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 - the extension will actually edit the $db,
$has_one etc.
// app/src/Extension/MyMemberExtension.php
namespace App\Extension;
use SilverStripe\ORM\DataExtension;
class MyMemberExtension extends DataExtension
{
private static $db = [
'Position' => 'Varchar',
];
private static $has_one = [
'Image' => Image::class,
];
}<%-- app/templates/Page.ss --%>
$CurrentMember.Position
$CurrentMember.ImageAdding methods
Methods that have a unique name will be called as part of the __call method on Object. In this example
we added a getGreeting method which is unique to our extension.
// app/src/Extension/MyMemberExtension.php
namespace App\Extension;
use SilverStripe\ORM\DataExtension;
class MyMemberExtension extends DataExtension
{
public function getGreeting()
{
// $this->owner refers to the original instance. In this case a `Member`.
return 'Hi ' . $this->owner->Name;
}
}<%-- app/templates/Page.ss --%>
<p>$CurrentMember.Greeting</p>
<%-- "Hi Sam" --%>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() 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', $validator);
// ...
}
// ...
}Extension Hooks can be located anywhere in the method and provide a point for any Extension instances to modify the
variables at that given point. In this case, the core function getValidator on the Member class provides an
updateValidator hook for developers to modify the core method. The MyMemberExtension would modify the core member's
validator by defining the updateValidator method.
// app/src/Extension/MyMemberExtension.php
namespace App\Extension;
use SilverStripe\ORM\DataExtension;
class MyMemberExtension extends DataExtension
{
public function updateValidator($validator)
{
// we want to make date of birth required for each member
$validator->addRequiredField('DateOfBirth');
}
}The $validator parameter is passed by reference, as it is an object.
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\Forms\FieldList;
use SilverStripe\Forms\TextField;
use SilverStripe\ORM\DataExtension;
class MyMemberExtension extends DataExtension
{
private static $db = [
'Position' => 'Varchar',
];
private static $has_one = [
'Image' => 'Image',
];
public 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 $foo;
}
}The convention for extension hooks is to provide an update{$FunctionOrProperty} hook at the end before you return the result. If
you need to provide extension hooks at the beginning of the method use before{..}.
Owner
In your Extension class you can only refer to the source object through the owner property on the class as
$this will refer to your Extension instance.
namespace App\Extension;
use SilverStripe\ORM\DataExtension;
class MyMemberExtension extends DataExtension
{
public function updateFoo($foo)
{
// outputs the original class
var_dump($this->owner);
}
}Please note that while you can read protected properties of the source object (using $this->owner->protectedProperty) you cannot call any of it's protected methods ($this->owner->protectedMethod() will not work). You also cannot access any of the source object's private properties or methods ($this->owner->privateProperty will not work either).
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.
$member = Security::getCurrentUser();
print_r($member->getExtensionInstances());
if ($member->hasExtension(MyCustomMemberExtension::class)) {
// ...
}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 Translatable 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()
{
$this->beforeExtending('populateDefaults', function () {
if (empty($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\TextField;
use SilverStripe\ORM\DataObject;
class MyModel extends DataObject
{
// ...
public function getCMSFields()
{
$this->beforeUpdateCMSFields(function ($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 overloaded 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 modifications such as this should be done in YAML configuration 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, and may not work consistently due to the "extra methods" cache having already been
populated.