How can I get all entities without a specific related entity? - mysql

Question

I have these tables:
users
id
name
events
id
name
entries
id
user_id
event_id
How can I get all users that do not have an entry with event_id 4?
With this code:
$users = User::query();
$users->leftJoin('entries', 'users.id', '=', 'entries.user_id')
->where('event_id','!=', $event_id)->get();
I still get users that already have an entry for that specific event.
This is what I want:
Get all entries which have event_id 4
Get the user_id from those entries
Remove other entries which have that user_id.
$entries = Entry::where(event_id, '=', 4)->get();
foreach ($entries as &$entry) {
//remove all entries from $entries array which "user_id = $entry->user_id"
}
How can I do the above with just a query?

Answer 1

Going by your question following is the answer but i guess this is not what you finally want. so elaborate more and specify the sample input and output datasets
select * from your_table where event_id <> 4;

Answer 2

The SQL you want is:
select user_id
from t
group by user_id
having sum(event_id = 4) = 0;

Answer 3

select u.*
from User u
left join entries e
on e.user_id = u.id and e.event_id = 4
where e.id is null

Answer 4

You're looking for <>, not !=. Also you're not letting it know which table event_id is on.
Try
$users = User::query();
$users->leftJoin('entries', 'users.id', '=', 'entries.user_id')
->where('entries.event_id','<>', $event_id)->get();
More information can be found at https://laravel.com/docs/5.4/queries#where-clauses

Answer 5

You can use the whereDoesntHave builder method.
$users = User::query()->whereDoesntHave("entry", function($q) use ($event_id) {
$q->where('id', $event_id);
})->get();
The method takes a closure in which you can define criteria for the related entities that must not exist.
If you need the users and the entries, I think you can still join the entries using with.
$users = User::query()
->with('entries')
->whereDoesntHave("entry", function($q) use ($event_id) {
$q->where('id', $event_id); })
->get();