How dows eager loading work for relations? - laravel

Question

I have read the docs I got that if call relation like: users()->author->name it sends another one request in db each time.
But if to call using User()::with("author") it will be loaded eager.
Therefore I try to understand how does it work if I call sometimes the method Auth::user() in controller:
public function controllerMethod(){
Auth::user()->tags();
/// Some logic
Auth::user()->id;
// Some logic
Auth::user()->tags();
}
Does it create a three the same requets in db or two the same and one additional with tags?
If yeas how toad it in global score because I need to get Auth::user() object everywehere in app to show the users fields.

Answer 1

User()::with() is actually an error:
Call to undefined function User()
The correct syntax would be User::with() 🙂
with() tells Laravel's Eloquent which relationship(s) to include when the query is executed. On its own, User::with('author') will not do much. When you use a closure, like ->get() or ->first(), it will execute a subquery, like:
SELECT * FROM authors WHERE user_id IN (...)
That IN (...) clause will change if you're loading a single User via ->first(), or multiple User instances via ->get(), but will make it so ->author doesn't need to call a new Database Query. Each $user->author property will be filled with an Author instance, or null (if that User doesn't have an Author, etc.)
Here's a quick example:
// Executes a single query to load each `User`
// Total Queries: 1
$users = User::get();
// Executes a new query on each loop
// Total Queries: 0 - ∞ (depends on number of loaded `User` instances)
foreach ($users as $user) {
$user->author->name;
}
// Executes a single Query to load each `User`, then a single subquery to load each `Author`
// Total Queries: 2
$users = User::with('author')->get();
foreach ($users as $user) {
$user->author->name;
}
When you call auth()->user(), that returns a single User instance, which has already been loaded from the Database. Calling auth()->user()->author will execute a new Query, since the User returned via auth()->user() didn't include ->with('author').
If you want to Eager Load a relationship on a User that has already been loaded from the Database, you'd call ->load('author'):
// Load the `User` instance from the database for the Authenticated User
$user = auth()->user();
// Executes the subquery `SELECT * FROM authors WHERE user_id = ?`
$user->load('author');
$user->author->name;
// Total Queries: 2
One catch, if you use ->author() (with the ()), it will execute a new Database query, even if you've already called ->load('author') (or ->with('author')):
$user = auth()->user();
$user->load('author'); // Subquery
$user->author()->first()->name; // ANOTHER Subquery
// Total Queries: 3
So the long and short of it is that ->with() will make accessing the relationship as a property, ->author (property) vs ->author()->first() (method), not include another Subquery. If you omit ->with('author'), then both ->author and ->author()->first() will perform a Subquery.