Let's look at a scenario where you must query the related records amount. A typical example would be loading the user with projects, and you need to show the amount of projects per user.
$users = User::with('projects')->get(); foreach ($users as $user) { print '<div><strong>' . $user->id . ': ' . $user->name . '</strong>: ' . $user->projects->count() . '</div>'; print '<hr />';}The result would look like this:
In this case, we load all the projects, which could be thousands across all users, which is not good for performance. But what if you only need the count of the projects?
In such a case, Laravel has a method withCount(). And then, instead of using relation and count, Laravel creates an attribute {relation}_count. In this example, it will be projects_count.
$users = User::withCount('projects')->get(); foreach ($users as $user) { print '<div><strong>' . $user->id . ': ' . $user->name . '</strong>: ' . $user->projects_count . '</div>'; print '<hr />';}In addition to the withCount() method, there are more aggregate functions withMin(), withMax(), withAvg(), withSum(), and withExists() methods. These methods will create an attribute with a name as {relation}_{function}_{column}.
$users = User::withMax('projects', 'id')->get(); foreach ($users as $user) { print '<div><strong>' . $user->id . ': ' . $user->name . '</strong>: ' . $user->projects_max_id . '</div>'; print '<hr />';}So these helpful methods will give you much better performance than loading the entire relationship with the with() method and then using collection methods to calculate in memory.