使用where子句从Laravel中的联接查询获取数据

Question

I am creating a system using Laravel and AngularJS where I assign tasks to users. Multiple tasks has multiple users and vice versa. In the Database, I have this tables:

task: id | name

task_users: id | task_id | user_id

users: id | name

In my view, I display a particular task, using id of task table. I display a list of users (called unassigned users) who are not assigned to that particular task. When that user is assigned, it's name gets removed from the list.

To achieve this, I used this query:

    public static function remainingUser($task_id)
    {
    return \DB::table('users')
        ->leftjoin('task_users', 'task_users.user_id', '=', 'users.id')
        ->select('users.id',
            'users.name as name'
        )
        ->where('task_id', '!=', $task_id)
        ->orWhere('task_id', null)
        ->get();
    }

Suppose I have this data

task:

id | name

1 | Task1

2 | Task2

3 | Task3

users:

id | name

1 | User1

2 | User2

3 | User3

4 | User4

5 | User5

6 | User6

7 | User7

8 | User8

9 | User9

10 | User10

task_users:

id | task_id | user_id

1 | 1 | 1

1 | 1 | 2

1 | 1 | 3

1 | 1 | 5

1 | 1 | 6

1 | 1 | 7

1 | 2 | 2

1 | 2 | 4

Now suppose I am displaying task details of task_id = 1 and I want to assign user 4 to this task. So my list of unassigned users should contain all the users who are not assigned this task. My query does not return the required data. I have also tried different conditions in where clause, but I do not get the correct required data. What am I doing wrong?

Answer 1

The issue exists because when you select from Users , you get all users left Joined with a single instance of tasks. So if User1 has Task1 and Task2 , only Task1 will be matched here, because it will match User1 to the 1st row found for him within task_users . In order to list the unasigned users, your query would look similar to this:

public static function remainingUser($task_id)
{
return \DB::table('task_users')
    ->rightJoin('users', 'task_users.user_id', '=', 'users.id')
    ->select(
      \DB::raw("DISTINCT(`users`.`id`)"),
      'users.name as name'
    )
    ->where('task_id', '!=', $task_id)
    ->orWhere('task_id', null)
    ->get();
}