如何获取不在laravel表下的belongsToMany关系下的用户列表? [英] how to get list of users who are not under belongsToMany relation under a table in laravel?

问题描述

请考虑以下情况. 我们有Users表和Tasks表.它们与表task_user中的belongsToMany有关.

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

如何获取不在任何任务下的所有用户的列表?即他们的user_id根本不在该给定任务下，甚至不在task_user表中.

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.

我之所以需要这样做是因为这样，我们只能提供尚未分配任务的用户列表.该任务将一次分配给用户，而不是一次分配给单个用户.

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.

编辑_____________

Editing_____________

还如何根据组表与用户进行过滤?下面不起作用

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();

推荐答案

假设您已正确命名关系，则应该可以使用doesntHave("tasks"):

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

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

doesntHave()检查是否存在所提供的关系(在本例中为"tasks")，并返回所有通过此检查的对象.

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

如果您的函数名称不同，请使用该名称，但关系应为:

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");
}

doesntHave()是简单版本，whereDoesntHave()允许自定义查询.参见 https://laravel.com/docs/5.8/eloquent-relationships #querying-relationship-absence 获取详细信息.

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.

第二次修改:

如下面的评论所述，with()不会过滤正在被调用的Model，因此此查询无法按您期望的那样工作:

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();

要解决此问题，请使用链接的doesntHave()查询:

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`)

这两种方法都会检查是否存在subscribers没有任何关联的tasks关系，并且只会在id是$gid的情况下返回.

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

注意:将first()用于查询，因为在查询中使用id只能返回单个Group记录，而get()用于返回Collection

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

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