php - Laravel 5 Eloquent hasManyThrough/belongsToManyThrough 关系

Question

在 Laravel 5.2 应用程序中，我有三个模型:User、Role 和 Task。一个 User 与多个 Roles 相关联，一个 Role 与多个 Tasks 相关联。因此，每个用户通过他们的角色关联到多个任务。

我正在尝试通过他们的角色访问与 User 关联的所有 Tasks。

我模型的相关部分如下所示:

class User extends Authenticatable
{    
    public function roles()
    {
        return $this->belongsToMany('App\Role');
    }

    public function tasks()
    {
        return $this->hasManyThrough('App\Task', 'App\Role');
    }
}

class Role extends Model
{
    public function tasks()
    {
        return $this->belongsToMany('App\Task');
    }

    public function users()
    {
        return $this->belongsToMany('App\User');
    }
}

class Task extends Model
{    
    public function roles()
    {
        return $this->belongsToMany('App\Role');
    } 
}

以下返回SQL错误；

Column not found: 1054 Unknown column 'roles.user_id'

它似乎试图通过角色模型中的(不存在的)外键访问关系，而不是通过数据透视表。

$user = Auth::user;
$tasks = $user->tasks;

如何通过这些关系访问与用户相关的所有任务？

Answer 1

我开发了一个 custom BelongsToManyThrough relationship你可能会感兴趣。您需要添加新的关系类(如我的要点中给出；粘贴到此处太长)，并且还需要按照要点中的描述覆盖您的基础 Model 类以实现 belongsToManyThrough 。

然后(假设您正在使用 Laravel 的默认表命名方案 - 如果没有，您也可以指定连接表)，您可以将您的关系定义为:

public function tasks()
{
    return $this->belongsToManyThrough(
        'App\Task',
        'App\Role');
}

belongsToManyThrough 不仅会为您提供用户的任务列表，还会告诉您每个用户拥有每个任务的角色。例如，如果您有:

$user->tasks()->get()

输出看起来像这样:

 [
    {
        "id": 2,
        "name": "Ban spammers",
        "roles_via": [
            {
                "id": 2,
                "slug": "site-admin",
                "name": "Site Administrator",
                "description": "This role is meant for \"site administrators\", who can basically do anything except create, edit, or delete other administrators."
            },
            {
                "id": 3,
                "slug": "group-admin",
                "name": "Group Administrator",
                "description": "This role is meant for \"group administrators\", who can basically do anything with users in their same group, except other administrators of that group."
            }
        ]
    },
    {
        "id": 13,
        "name": "Approve posts",
        "roles_via": [
            {
                "id": 3,
                "slug": "group-admin",
                "name": "Group Administrator",
                "description": "This role is meant for \"group administrators\", who can basically do anything with users in their same group, except other administrators of that group."
            }
        ]
    },
    {
        "id": 16,
        "name": "Reboot server",
        "roles_via": [
            {
                "id": 2,
                "slug": "site-admin",
                "name": "Site Administrator",
                "description": "This role is meant for \"site administrators\", who can basically do anything except create, edit, or delete other administrators."
            }
        ]
    }
]

与涉及 foreach 的其他解决方案相比，我的自定义关系可以高效地执行此操作，这将创建一个 n+1 query问题。