Laravel - can't find() attached object in many-to-many relationship - php

Question

in my POST form users are able to add other users to a room.
I put a unique constraint on the link (no duplicate entry in the link between users and rooms).
However when I refresh my page (f5) after submitting the form, Laravel complains about duplicate entries, although I do check if the objects are attached before.
Here's the code:
$roomUsers = Room::find($request->room_id)->users();
if ($request->add != null) {
foreach ($request->add as $uId)
// if null, user hasnt been attach yet
if (!$roomUsers->find($uId)) {
Log::debug($roomUsers->find($uId) == null ? 'null' : 'not null');
// then we can attach him
$roomUsers->attach($uId);
}
}
The line !$roomUsers->find($uId) returns true yet the object has been attached in the previous iteration. How is that possible ? Thanks

Answer 1

The reason you're above code isn't working is because you're not creating a new instance of BelongsToMany for each check. This means that every time you call find you're not actually creating a new query you're just adding to the existing one e.g.
say you the ids to add are [1, 2, 3] by the last check your query would effectively be:
SELECT * FROM users WHERE id = 1 AND id = 2 AND id = 3
To keep with the above logic you could do:
$room = Room::find($request->room_id);
if ($request->add != null) {
foreach ($request->add as $uId)
// if null, user hasnt been attach yet
if (!$room->users()->find($uId)) {
// then we can attach him
$room->users()->attach($uId);
}
}
Or a much simpler way to go about this would be to syncWithoutDetaching.
Your code could then look something like:
$roomUsers = Room::find($request->room_id);
if ($request->has('add')) {
$roomUsers->users()->syncWithoutDetaching($request->add);
}
Hope this helps!