Parental

Parental is a Laravel package that brings STI (Single Table Inheritance) capabilities to Eloquent.

What is single table inheritance (STI)?

It's a fancy name for a simple concept: Extending a model (usually to add specific behavior), but referencing the same table.

Installation

composer require tightenco/parental

Simple Usage

namespace App\Models;

use Illuminate\Database\Eloquent\Model;
use Parental\HasChildren;

// The "parent"
class User extends Model
{
    use HasChildren;
    //
}

namespace App\Models;

use Parental\HasParent;

// The "child"
class Admin extends User
{
    use HasParent;

    public function impersonate($user) {
        //...
    }
}

use App\Models\Admin;

// Returns "Admin" model, but reference "users" table:
$admin = Admin::first();

// Can now access behavior exclusive to "Admin"s
$admin->impersonate($user);

What problem did we just solve?

Without Parental, calling Admin::first() would throw an error because Laravel would be looking for an admins table. Laravel generates expected table names, as well as foreign keys and pivot table names, using the model's class name. By adding the HasParent trait to the Admin model, Laravel will now reference the parent model's class name users.

Accessing Child Models from Parents

// First, we need to create a `type` column on the `users` table
Schema::table('users', function ($table) {
    $table->string('type')->nullable();
});

namespace App\Models;

use Illuminate\Database\Eloquent\Model;
use Parental\HasChildren;

// The "parent"
class User extends Model
{
    use HasChildren;

    protected $fillable = ['type'];
}

namespace App\Models;

use Parental\HasParent;

// A "child"
class Admin extends User
{
    use HasParent;
}

namespace App\Models;

use Parental\HasParent;

// Another "child"
class Guest extends User
{
    use HasParent;
}

use App\Models\Admin;
use App\Models\Guest;
use App\Models\User;

// Adds row to "users" table with "type" column set to: "App/Admin"
Admin::create(...);

// Adds row to "users" table with "type" column set to: "App/Guest"
Guest::create(...);

// Returns 2 model instances: Admin, and Guest
User::all();

What problem did we just solve?

Before, if we ran: User::first() we would only get back User models. By adding the HasChildren trait and a type column to the users table, running User::first() will return an instance of the child model (Admin or Guest in this case).

Type Aliases

If you don't want to store raw class names in the type column, you can override them using the $childTypes property.

namespace App\Models;

use Illuminate\Database\Eloquent\Model;
use Parental\HasChildren;

class User extends Model
{
    use HasChildren;

    protected $fillable = ['type'];

    protected $childTypes = [
        'admin' => Admin::class,
        'guest' => Guest::class,
    ];
}

Now, running Admin::create() will set the type column in the users table to admin instead of App\Models\Admin.

This feature is useful if you are working with an existing type column, or if you want to decouple application details from your database.

Custom Type Column Name

You can override the default type column by setting the $childColumn property on the parent model.

namespace App\Models;

use Illuminate\Database\Eloquent\Model;
use Parental\HasChildren;

class User extends Model
{
    use HasChildren;

    protected $fillable = ['parental_type'];

    protected $childColumn = 'parental_type';
}

Transforming Models Between Types

You may transform a model from one type to another using the become() method.

namespace App\Models;

use Illuminate\Database\Eloquent\Model;
use Parental\HasChildren;
use Parental\HasParent;

class Order extends Model
{
    use HasChildren;

    protected $fillable = ['type', 'total'];

    protected $childTypes = [
        'pending' => PendingOrder::class,
        'shipped' => ShippedOrder::class,
    ];
}

class PendingOrder extends Order
{
    use HasParent;
}

class ShippedOrder extends Order
{
    use HasParent;
}

use App\Models\Order;
use App\Models\ShippedOrder;

// Retrieve a pending order
$order = Order::first();

// Ship the order by transforming it
$order = $order->become(ShippedOrder::class);

// Updates the "type" column to "shipped" and returns a ShippedOrder instance
$order->save();

What problem did we just solve?

The become() method will return a new instance of the specified child model with all the attributes of the original model. You must call save() on the returned model to persist the change to the database. This allows you to easily transition a model between different types while maintaining its data integrity, such as changing an order from pending to shipped, or a draft post to a published post.

This is also useful when you're using observers or callbacks, since the specific child model's behavior will be triggered after the transition.

A new model event is fired when a model is becoming another type, you may listen to it like so:

ShippedOrder::becoming(function ($shippedOrder) {
    // Do something before the model is saved...
});

Laravel Nova Support

If you want to use share parent Nova resources with child models, you may register the following provider at the end of the boot method of your NovaServiceProvider:

class NovaServiceProvider extends NovaApplicationServiceProvider
{
    public function boot() {
        parent::boot();
        // ...
        $this->app->register(\Parental\Providers\NovaResourceProvider::class);
    }
}

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Thanks to @sschoger for the sick logo design, and @DanielCoulbourne for helping brainstorm the idea on Twenty Percent Time.