dougou5844
2016-07-01 06:15 阅读 212
已采纳

通过Laravel中多对多关系的has-many-through检索远程关系

I have the following models in my application

  • User
  • Group
  • Task

which have the following relationships

  • User and Group have a many-to-many relationship
  • Task and Group have a many-to-many relationship

So basically a user can belong to more than one group and each group can have more than one task.

Following is the table structure.

users

  • id
  • name

groups

  • id
  • name

tasks

  • id
  • name

group_user

  • id
  • group_id (foreign key with groups table)
  • user_id (foreign key with users table)

group_tasks

  • id
  • group_id (foreign key with groups table)
  • task_id (foreign key with tasks table)

Now I want to retrieve all the tasks for the user.

I tried the following approaches and both didn't work.

Approach 1

  • $user->groups() gives the list of groups for a user
  • $group->tasks() gives the list of tasks for a group

So I tried

$user->groups()->tasks() but it didn't work.

Approach 2

I tried Has Many Through by adding this to my User model

public function tasks()
{
    return $this->hasManyThrough(Task::class, Group::class);
}

but even that didn't work. The following is the error that I am getting

QueryException in Connection.php line 713:
SQLSTATE[42S22]: Column not found: 1054 Unknown column 'groups.user_id' in 'field list' (SQL: select `tasks`.*, `groups`.`user_id` from `tasks` inner join `groups` on `groups`.`id` = `tasks`.`group_id` where `groups`.`user_id` = 1)

My guess is that this is happening because it is expecting one-to-many relationship, but I have a many-to-many relationship.

So is there a way to retrieve it without getting all groups and then looping through them?

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2条回答 默认 最新

  • 已采纳
    dt614037527 dt614037527 2016-07-01 10:53
    User Model
    
    public function groups()
    {
        return $this->belongsToMany('App\Group');
    }
    
    Group Model
    
    public function tasks()
    {
        return $this->belongsToMany('App\Task');
    }
    
    Task Model
    
    public function groups()
    {
        return $this->belongsToMany('App\Group');
    }
    

    Retrieving all tasks for a user.

    $user = User::find(1);
    
    $user->load('groups.tasks');
    
    $tasks = $user->groups->pluck('tasks')->collapse();
    
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  • dqyuipw44576 dqyuipw44576 2019-02-14 15:24

    You can also take a look at the extension of the HasManyThrough here: https://github.com/staudenmeir/eloquent-has-many-deep

    It helps you to retrieve many sub-levels of your relationships. In your case, it would be User -> belongsToMany(Groups) -> blongsToMany (Tasks) just add your method to the user model like:

    public function tasks()
        {
            return $this->hasManyDeep(
                'App\Task',['App\Group']
            );
        }
    
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