how to get list of users who are not under belongsToMany relation under a table in laravel?

问题

Consider the following case. we have the Users table and Tasks table. they are in relation with belongsToMany with table task_user.

How to get the list of all users who are not under any task? i.e. their user_id is not at all under that given task or even in the task_user table.

why I need this is because like this we can only provide a list of users who are yet to be assigned a task. the task will be assigned to users and not a single user at a time.

Editing_____________

also how to filter with users based on group table? below is not working

$users = Group::with(['subscribers' => function ($q){
            $q->doesntHave("tasks");
        }])->whereId($gid)->latest()->get();

回答1:

Assuming you've named your relationships properly, you should be able to use doesntHave("tasks"):

$tasklessUsers = User::doesntHave("tasks")->get();

doesntHave() checks for the non-existence of the supplied relationship ("tasks", in this case) and returns all objects that pass this check.

If your function name is different, use that, but the relationship should be:

User.php:

public function tasks(){
  return $this->belongsToMany(Task::class, "task_user");
}

Edit: doesntHave() is the simple version, whereDoesntHave() allows a custom query. See https://laravel.com/docs/5.8/eloquent-relationships#querying-relationship-absence for full details.

Second Edit:

As stated in the comments below, with() will not filter the Model it is being called on, so this query won't work as you'd expect:

$users = Group::with(['subscribers' => function ($q){
  $q->doesntHave("tasks");
}])->whereId($gid)->latest()->get();

To fix this, use a chained doesntHave() query:

$query = Group::doesntHave('subscribers.tasks')
->where('id', '=', $gid)
->latest()
->first();

// OR

$query = Group::whereHas('subscribers', function($subQuery){
  $subQuery->doesntHave('tasks');
})->where('id', '=', $gid)
->latest()
->first();

$users = $query->subscribers; // Return `users` (aliased to `subscribers`)

Either approach will check the existence of subscribers that don't have any associated tasks relationship, and also only return where id is $gid.

Note: Used first() for the queries, as using id in a query should only ever return a single Group record, and get() is for returning multiple records in a Collection

来源：https://stackoverflow.com/questions/59273470/how-to-get-list-of-users-who-are-not-under-belongstomany-relation-under-a-table

标签

laravel

eloquent

relation