Dynamic Class Mapper

Extending PHP classes is a little different from extending other types of entities. You cannot simply replace a class by redefining it in a custom Sprinkle. In fact, classes with the same name in two different Sprinkles would be treated as two different fully-qualified classes per the PSR-4 standard. For example, if I loaded the Sprinkles Account and Site, and I had the following structure:

sprinkles
├── account
│   └── src
│       └── Database
│           └── Models
│               └── User.php
├── site
│   └── src
│       └── Database
│           └── Models
│               └── User.php

...then User.php in site would not override User.php in account. Rather, I'd have two different classes because both classes would have two different namespace : \UserFrosting\Sprinkle\Account\Database\Models\User and \UserFrosting\Sprinkle\Site\Database\Models\User.

To actually override and replace the functionality of a class, we have two tools available:

Class Inheritance

We could, for example, define our User class in the site Sprinkle to inherit from the User class in account using the extends keyword:

app/sprinkles/site/src/Database/Models/User.php :

<?php

namespace \UserFrosting\Sprinkle\Site\Database\Models;

class User extends \UserFrosting\Sprinkle\Account\Database\Models\User
{
    ...
}

Now, we can start using \UserFrosting\Sprinkle\Site\Database\Models\User to extend the functionality provided by the User class in the Account sprinkle.

Dynamic Class Mapper

Of course, the limitations of object-oriented inheritance becomes clear when you want to change the behavior of the original class in other places where it has been used. For example, if I extended Account\Database\Models\User and redefined the onLogin method in my Site\Database\Models\User class, this would let me use Site\Database\Models\User going forward in any code I write in the site Sprinkle. However, it wouldn't affect references to User in the account Sprinkle - they would still be referring to the base class.

To allow this sort of "retroactive extendability", UserFrosting introduces another layer of abstraction - the class mapper. The class mapper resolves generic class identifiers to specific class names at runtime. Rather than hardcoding references to Account\Database\Models\User, Sprinkles can generically reference user through the class mapper, and it will find the most recently mapped version of that class.

For example, a controller in the account Sprinkle could do something like:

$user = $classMapper->staticMethod('user', 'where', 'email', '[email protected]')->first();

The account Sprinkle itself maps the user identifier to UserFrosting\Sprinkle\Account\Database\Models\User. Thus, this call would be equivalent to:

$user = \UserFrosting\Sprinkle\Account\Database\Models\User::where('email', '[email protected]')->first();

However, if I later re-map the user identifier to \UserFrosting\Sprinkle\Site\Database\Models\User, then all calls to $classMapper->staticMethod('user', ...) in any Sprinkle will dynamically resolve to \UserFrosting\Sprinkle\Site\Database\Models\User instead.

Dynamic class mappings are typically defined by extending the classMapper service in your Sprinkle's service provider:

app/sprinkles/account/src/ServicesProvider/ServicesProvider.php:

$container->extend('classMapper', function ($classMapper, $c) {
    $classMapper->setClassMapping('user', 'UserFrosting\Sprinkle\Account\Database\Models\User');
    $classMapper->setClassMapping('group', 'UserFrosting\Sprinkle\Account\Database\Models\Group');
    $classMapper->setClassMapping('role', 'UserFrosting\Sprinkle\Account\Database\Models\Role');
    $classMapper->setClassMapping('permission', 'UserFrosting\Sprinkle\Account\Database\Models\Permission');
    $classMapper->setClassMapping('activity', 'UserFrosting\Sprinkle\Account\Database\Models\Activity');

    return $classMapper;
});

You can learn more about services in Chapter 15.

Note that it's not just database models that you can dynamically remap (though they are the most common use case!) Any class references that haven't been hardcoded can be dynamically remapped in another Sprinkle's classMapper service.

Default Model Identifiers

See the Services Chapter for a list of default model identifiers defined by the Account sprinkle.