How to write a query to get a result from another table?

Question

Laravel

There is a task:

I'm trying to do this:
Take the user's Auth and compare its value with the Auth of another table.
If the values ​​match, then display the amount of money for the current user.
So far the following has happened:

$auth = Auth::user()->auth;
 $lk = App\Models\Lk::select('cash','auth')->where('auth',$auth)->get();

But the $lk variable returns NULL .
Where am I doing wrong?

Answer 1

The cash field is not in the second table.
Relationships should be used https://laravel.com/docs/8.x/eloquent-relationships