Laravel 5 雄辩的 hasManyThrough/belongsToManyThrough 关系

问题描述

在 Laravel 5.2 应用程序中，我有三个模型:User、Role 和 Task.一个User关联多个Roles，一个Role关联多个Tasks.因此，每个用户都通过他们的角色与多个任务相关联.

In a Laravel 5.2 application I have three models: User, Role and Task. A User is associated with multiple Roles, and a Role is associated with multiple Tasks. Therefore each user is associated to multiple tasks, through their roles.

我正在尝试通过他们的角色访问与 User 关联的所有 Tasks.

I am trying to access all Tasks associated with a User, through their Roles.

我的模型的相关部分如下所示:

The relevant parts of my models look like:

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

    public function tasks()
    {
        return $this->hasManyThrough('AppTask', 'AppRole');
    }
}

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

    public function users()
    {
        return $this->belongsToMany('AppUser');
    }
}

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

以下返回SQL错误；

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

它似乎试图通过 Role 模型中的(不存在的)外键访问关系，而不是通过数据透视表.

It seems to be trying to access the relationship through a (non-existent) foreign key in the Role model, rather than through the pivot table.

$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?

How can I access all tasks related to a user through these relationships?

推荐答案

我开发了一个自定义BelongsToManyThrough 关系，您可能会感兴趣.您需要添加新的关系类(在我的要点中给出；粘贴在这里太长了)，并且还需要按照要点中的描述覆盖您的基本 Model 类以实现 belongsToManyThrough.

I have developed a custom BelongsToManyThrough relationship which might interest you. You would need to add the new relation class (as given in my gist; it is too long to paste here), and also override your base Model class as described in the gist to implement belongsToManyThrough.

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

Then (assuming you are using Laravel's default table naming schemes - if not, you can specify the joining tables as well), you would define your relationship as:

public function tasks()
{
    return $this->belongsToManyThrough(
        'AppTask',
        'AppRole');
}

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

belongsToManyThrough will not only give you a list of Tasks for your User(s), it will also tell you the Role(s) via which each User has each Task. For example, if you had:

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

输出将类似于:

 [
    {
        "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."
            }
        ]
    }
]

我的自定义关系有效地完成了这项工作，只需要几个查询，而不是其他涉及 foreach 的解决方案，后者会创建一个 n+1 查询 问题.

My custom relationship does this efficiently, with only a few queries, as opposed to other solutions involving foreach, which would create an n+1 query problem.

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