Null Safety in Laravel (Null Object Pattern)

Introduction

Null Object Pattern in Programming is a design pattern that is used to avoid null references by providing a default object.

Null Object Pattern in Laravel

Let's explore this pattern in Laravel. We will use a simple example to explain the concept.

Assume we have a User model and a Post model having a one-to-many relationship setup like this:

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Model;

class User extends Model
{
    public function posts()
    {
        return $this->hasMany(Post::class);
    }
}

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Model;

class Post extends Model
{
    public function user()
    {
        return $this->belongsTo(User::class);
    }
}

In our controller after fetching a post, we can load the user relationship like this and send it to the view:

<?php

namespace App\Http\Controllers;

use App\Http\Controllers\Controller;

class PostController extends Controller
{
    public function show(Post $post)
    {
        $post = $post->load('user');

        return view('post.show', ['post' => $post]);
    }
}

In our blade file, we can access the user's name like this:

// post.show.blade.php
// ...
{{ $post->user->name }}
// ...

The problem with this approach is that if the user happens to be null, we will get an error like this:

Trying to get property 'name' of non-object

This is the most common error in Laravel and programming in general. The traditional way to solve this problem is to use conditional statements to check for null safety before accessing the property.

So, in our blade file, we can do something like this to avoid the error:

// post.show.blade.php
// ...
@if($post->user)
    {{ $post->user->name }}
@endif
// ...

This approach works, but it is not the best way to solve this problem.

The Null Object Pattern in Laravel

Let's apply the Null Object Pattern to solve this problem.

We'll modify our Post model to use withDefault method on the user relationship:

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Model;

class Post extends Model
{
    public function user()
    {
        return $this->belongsTo(User::class)
        ->withDefault([
            'name' => 'Unknown user',
        ]);
    }
}

Now, if the user is null, we will get the default user object with the name set to Unknown user; therefore we don't have to worry about null safety in our blade file.

// post.show.blade.php
{{ $post->user->name }}

We can also supply a fallback model instance to the withDefault method like this:

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Model;

class Post extends Model
{
    public function user()
    {
        return $this->belongsTo(User::class)
        ->withDefault(NullUser::make()->toArray());
    }
}

And the NullUser class will look something like this:

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Model;

class NullUser extends User
{
    protected $attributes = [
        'name' => 'Unknown user',
    ];
}

Now, if the user is null, we will get the NullUser instance with the name set to Unknown user.

Conclusion

In this article, we learned how to implement the Null Object Pattern in Laravel and how it can help us avoid null references. For more information, you can check out the official documentation.