Performance + Advanced Eloquent + Transactions

 

N+1 query problem

Interview answer

N+1 occurs when one query retrieves the parent records and then one additional query runs for each parent.

$users = User::all();

foreach ($users as $user) {
    echo $user->orders->count();
}

If there are 1,000 users, this can result in roughly:

1 query for users
+ 1,000 queries for orders
= 1,001 queries

Fix:

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

For large datasets, I also consider whether I actually need the complete relationship data.

For example:

$users = User::withCount('orders')->get();

Then:

$user->orders_count;

may be much cheaper than loading every order.