title: Extending DataObjects
summary: Modify the data model without using subclasses.

# Extending DataObjects

You can add properties and methods to existing [DataObject](api:SilverStripe\ORM\DataObject)s like [Member](api:SilverStripe\Security\Member) without hacking core code or sub 
classing by using [DataExtension](api:SilverStripe\ORM\DataExtension). See the [Extending SilverStripe](../extending) guide for more information on
[DataExtension](api:SilverStripe\ORM\DataExtension).

The following documentation outlines some common hooks that the [Extension](api:SilverStripe\Core\Extension) API provides specifically for managing
data records.

## onBeforeWrite

You can customise saving-behavior for each DataObject, e.g. for adding workflow or data customization. The function is 
triggered when calling *write()* to save the object to the database. This includes saving a page in the CMS or altering 
a `ModelAdmin` record.

Example: Disallow creation of new players if the currently logged-in player is not a team-manager.

```php
use SilverStripe\Security\Security;
use SilverStripe\ORM\DataObject;

class Player extends DataObject 
{
    private static $has_many = [
        "Teams" => "Team",
    ];
    
    public function onBeforeWrite() 
    {
        // check on first write action, aka "database row creation" (ID-property is not set)
        if(!$this->isInDb()) {
            $currentPlayer = Security::getCurrentUser();
        
            if(!$currentPlayer->IsTeamManager()) {
                user_error('Player-creation not allowed', E_USER_ERROR);
                exit();
            }
        }
        
        // check on every write action
        if(!$this->record['TeamID']) {
            user_error('Cannot save player without a valid team', E_USER_ERROR);
            exit();
        }
        
        // CAUTION: You are required to call the parent-function, otherwise
        // SilverStripe will not execute the request.
        parent::onBeforeWrite();
    }
}

```

## onBeforeDelete

Triggered before executing *delete()* on an existing object.

Example: Checking for a specific [permission](permissions) to delete this type of object. It checks if a 
member is logged in who belongs to a group containing the permission "PLAYER_DELETE".

```php
use SilverStripe\Security\Permission;
use SilverStripe\Security\Security;
use SilverStripe\ORM\DataObject;

class Player extends DataObject 
{
    
    private static $has_many = [
        "Teams" => "Team"
    ];
    
    public function onBeforeDelete() 
    {
        if(!Permission::check('PLAYER_DELETE')) {
            Security::permissionFailure($this);
            exit();
        }
        
        parent::onBeforeDelete();
    }
}
```

<div class="notice" markdown='1'>
Note: There are no separate methods for *onBeforeCreate* and *onBeforeUpdate*. Please check `$this->isInDb()` to toggle 
these two modes, as shown in the example above.
</div>

## Related Lessons
* [Working with data relationships - $has_many](https://www.silverstripe.org/learn/lessons/v4/working-with-data-relationships-has-many-1)