Mastering Eager Loading and Solving the N+1 Issue in Laravel

Eloquent is a powerful tool that simplifies database interactions in your web applications. However, some key features are often not understood, one of which is is eager loading, which allows you to fetch relationships efficiently. In this article, we will explore how to leverage eager loading and solve the N+1 issue.

Understanding the N+1 Issue

Imagine you have two models: User and Post. Each user can have multiple posts, and you want to retrieve all users along with their posts. Without eager loading, the default lazy loading behavior can lead to the N+1 issue.

$users = User::all();

foreach ($users as $user) {
    // Lazy load the posts for each user
    $posts = $user->posts;

    // Do something with the posts
    foreach ($posts as $post) {
        // ...
    }
}

In the code snippet above, if you have 10 users, it would result in 1 query to fetch the users (SELECT * FROM users), and then an additional 10 queries to fetch the posts for each user (SELECT * FROM posts WHERE user_id = ?). This creates the N+1 problem, where the number of queries grows linearly with the number of parent records.

Introducing Eager Loading

To overcome the N+1 issue, Laravel offers eager loading. With eager loading, you can fetch the necessary data in a more efficient way. Let's take a look at how to use eager loading to retrieve users and their posts.

$users = User::with('posts')->get();

foreach ($users as $user) {
    // Access the eagerly loaded posts directly
    $posts = $user->posts;

    // Do something with the posts
    foreach ($posts as $post) {
        // ...
    }
}

In the updated code, we use the with('posts') method to specify that we want to eagerly load the posts relationship for each user. The get() method then retrieves all the users along with their posts in just 2 queries: one to fetch the users and another to fetch all the related posts. By utilizing eager loading, we effectively reduce the number of queries from N+1 to 2, significantly improving performance.

Enforcing Eager Loading

Laravel provides a convenient way to enforce eager loading throughout your application. You can use the Model::preventLazyLoading() method to disable lazy loading globally. By calling this method, Laravel will throw an exception if lazy loading is attempted, ensuring that you always use eager loading.

This can be achieved by adding the following to the boot method of the AppServiceProvider

<php

namespace App\Providers;
 
use Illuminate\Support\ServiceProvider;
 
class AppServiceProvider extends ServiceProvider
{
	public function boot(): void
	{
		Model::preventLazyLoading();
	}
}