Laravel (Lumen) Eloquent querying with WHERE on a relation (Multi-level) - mysql

Question

I have the following DB tables:
Purchase
-id
-workplace_id
Workplace
-id
-client_id
(and obviously some more fields, but for the example these are all the needed ones).
I would like to make a query like this:
SELECT * FROM
purchase
INNER JOIN workplace ON (purchase.workplace_id = workplace.id)
WHERE
(workplace.client_id = 1)
I'm trying to make this work with the Eloquent models, but I can't figure out how to filter on a joined table.
I tried:
$purchases = Purchase::query()
-> workplace()
-> where('client_id', '=', Auth::user() -> client_id)
-> get();
But apparently workplace() is undefined for some reason.
My Purchase.php model file looks like this:
<?php
namespace App\Models;
use Illuminate\Database\Eloquent\Model;
class Purchase extends Model
{
public function workplace(): \Illuminate\Database\Eloquent\Relations\BelongsTo
{
return $this->belongsTo(Workplace::class);
}
}
Any pointers on how to make this simple select work?
Thanks!
====EDIT=====
I found a possible solution:
$purchases = Purchase::with('workplace')
-> whereHas('workplace', function($q) {
return $q -> where('client_id', '=', Auth::user() -> client_id);
})
-> get();
But this generates an SQL that seems more complicated and is probably also slower:
select * from `purchases` where exists (select * from `workplaces` where `purchases`.`workplace_id` =
`workplaces`.`id` and `client_id` = ? and `workplaces`.`deleted_at` is null)
So I'm still looking for better alternatives

Answer 1

If you want to do a join, you need to build it with the join method, you can't use a relationship. See here for the docs:
https://laravel.com/docs/9.x/queries#joins
So you should be able to do something like this:
$purchases = Purchase::query()
->join('workplace', 'purchase.workplace_id', '=', 'workplace.id')
->where('workplace.client_id', '=', Auth::user()->client_id)
->get();
The generated SQL that you show in your edit is a sub-query, and you may still want to consider that. Sure, sub-queries are often slower than joins, but unless you're dealing with a massive dataset the performance difference might be negligible, and it allows you to use native Eloquent relationships.
See here for a discussion on this: https://stackoverflow.com/a/2577188/660694