Eloquent; getting rows not in other table - eloquent

Question

I'm trying to get a list of records from a table, where the PK is not in a composite table. If you see consider below table, I'm trying to get all candidates that are not in a pool, so in this case I should get only Eric.
+-------------+ +-------------+
| candidates | | pools |
+-------------+ +-------------+
| id | name | | id | name |
+----+--------| +----+--------|
| 1 | John | | 1 | Pool A |
| 2 | Richard| | 2 | Pool B |
| 3 | Eric | | 3 | Pool C |
+----+--------+ +----+--------+
+--------------------------+
| candidate_pools |
+--------------------------+
| pool_id | candidate_id |
+---------+----------------|
| 1 | 1 |
| 1 | 2 |
| 3 | 2 |
| 2 | 1 |
+---------+----------------+
I've found this answer: https://laracasts.com/discuss/channels/eloquent/get-records-collection-if-not-exists-in-another-table
$crashedCarIds = CrashedCar::pluck('car_id')->all();
$cars = Car::whereNotIn('id', $crashedCarIds)->select(...)->get();
Which should work, however it seems extremely inefficient in our fairly big and rapidly growing database, on a page that is accessed often by a lot of people.
In normal MySQL you would do something like this:
WHERE candidates.id NOT IN
( SELECT candidate_id
FROM candidate_pools
LEFT JOIN pools
ON candidate_pools.pool_id = pool.id
)
Note: The tables are just a simple illustration, but the actual database set-up and queries are a lot bigger.

Answer 1

I managed to do it using scope, like this:
public function scopeNotInPool($query) {
$query->whereNotIn('candidate_id', function ($query) {
$query->select('candidate_id')
->from('candidate_pool')
->join('pool', function ($join) {
$join->on('pool.id', '=', 'candidate_pool.pool_id');
}
)
;
});
return $query;
}
Then call it like:
$candidates = Models\Candidate::notInPool()->get();