16 Sep 2020

Eloquent Performance: Reusable relationships

Sometimes we end up causing N+1 problems by reloading the same relationships that we already loaded.

Let's say that you have a method named isAuthor() in the App\Models\Comment.

The method determines whether the author of the comment is the same author of the post:

// App\Models\Comment

public function isAuthor(): bool
    return $this->post->user_id === $this->user_id;
// App\Controllers\PostsController

$post = Post::where('id', $id)

return view('posts.show', compact('post'));

In the template we show a badge if the comment's author is the same as the post's author:

@foreach ($post->comments as $comment)
<div class="card">
    <div class="card-body">
        <h6 class="card-title">Published at {{ $comment->created_at->toFormattedDateString() }}
            by {{ $comment->user->name }}
            @if ($comment->isAuthor())
                <span class="badge badge-warning">Author</span>
        <p class="card-text">{{ $comment->comment }}</p>
<div class="m-4"></div>

As you see in the template, the isAuthor() method was called inside the foreach (N+1 problem).

Since the App\Models\Post was already loaded in the controller, can't we reuse it instead of calling the database again to fetch the same model (App\Models\Post)?

Yes, we can do that by using the setRelation() method on the Illuminate\Database\Eloquent\Collection:

// App\Controllers\PostsController

$post = Post::where('id', $id)->with('comments.user')->first();

// This is our fix
$post->comments->each->setRelation('post', $post);

return view('posts.show', compact('post'));

No N+1 problem, that's amazing.

In the next post, I will discuss counting records in a single query.