What is Eager Loading and why is it important in Laravel?

Question

What is the N+1 query problem and how does eager loading solve it in Laravel?

Answer

The N+1 problem occurs when you load a collection of records and then access a relationship on each one individually, causing one extra query per record:

// ❌ N+1 — 1 query for posts + 1 query per post for its author
$posts = Post::all(); // 1 query
foreach ($posts as $post) {
    echo $post->author->name; // 1 query × N posts = N queries
}
// Total: 1 + N queries

Eager loading with with() resolves the relationship in just 2 queries total:

// ✅ Eager loading — 2 queries total regardless of record count
$posts = Post::with('author')->get();
foreach ($posts as $post) {
    echo $post->author->name; // no extra query
}

Loading Multiple & Nested Relationships

$posts = Post::with(['author', 'tags', 'comments.user'])->get();

Constrained Eager Loading

$posts = Post::with([
    'comments' => fn ($q) => $q->where('approved', true)->latest()->limit(5),
])->get();

Detecting N+1 in Development

// AppServiceProvider::boot()
Model::preventLazyLoading(! app()->isProduction());