Eager loading prevents the N 1 query problem by loading relationships upfront. The N 1 problem occurs when 1 query fetches records (e.g., 100 posts) and N additional queries fetch related data (e.g., author for each post), resulting in 101 queries. Eager loading fixes this: 1 query retrieves all posts, and 1 query retrieves all authors. Use with() to eager load: Post::with('author')->get() loads posts and authors in 2 queries. Multiple relationships: Post::with(['author', 'comments', 'tags'])->get(). Nested: Post::with('author.profile')->get(). Constrained: Post::with(['comments' => function ($query) { $query->where('is_approved', true); }])->get(). Use eager loading when accessing relationships in loops, especially in APIs or views. Avoid load() inside loops as it can still cause N 1. Eager loading improves performance by reducing database queries.
Eager loading in Laravel is a technique used to load relationships on models in a way that prevents the N 1 query problem, making your application more efficient and faster.
What is the N 1 Problem?
Imagine you're displaying a list of 100 blog posts, and each post has an author (a relationship). Without eager loading, Laravel might run:
- 1 query to get the 100 posts
- Then, 1 additional query for each post to load its author
That’s 101 queries — this is the N 1 problem (1 N queries). It’s slow and inefficient.
How Eager Loading Fixes This
Eager loading lets you load the posts and their authors in just 2 queries:
$posts = Post::with('author')->get();This runs:
- 1 query for all posts
- 1 query to get all related authors at once
Now, when you loop through the posts, accessing $post->author doesn’t trigger a new database query.
Key Points About Eager Loading
- Use
with()to specify which relationships to eager load - Works with one-to-many, many-to-many, nested relationships
- You can eager load multiple relationships:
Post::with(['author', 'comments', 'tags'])->get();
- Supports nested relationships:
Post::with('author.profile')->get();- You can even add constraints:
Post::with(['comments' => function ($query) {
$query->where('is_approved', true);
}])->get();When Should You Use It?
Use eager loading whenever you know you’ll access model relationships in a loop. It's especially important in APIs, views with lists, or any performance-sensitive area.
? Tip: If you're looping through models and calling a relationship inside the loop (e.g., in Blade), you probably need eager loading.
Lazy Eager Loading (Not Recommended in Loops)
Laravel also allows load() after the models are retrieved:
$posts = Post::all();
$posts->load('author');But this should be used carefully — it doesn’t solve N 1 if called inside a loop.
Basically, eager loading is about being smart with database queries — loading related data upfront instead of fetching it one by one. In Laravel, with() is your best friend for this.
The above is the detailed content of What is eager loading in Laravel?. For more information, please follow other related articles on the PHP Chinese website!
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