問題描述

在 Laravel 5.2 應用程序中，我有三個模型:User、Role 和 Task.一個User關聯多個Roles，一個Role關聯多個Tasks.因此，每個用戶都通過他們的角色與多個任務相關聯.

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.

我正在嘗試通過他們的角色訪問與 User 關聯的所有 Tasks.

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

我的模型的相關部分如下所示:

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錯誤；

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

它似乎試圖通過 Role 模型中的(不存在的)外鍵訪問關系，而不是通過數據透視表.

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;

如何通過這些關系訪問與用戶相關的所有任務?

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

推薦答案

我開發了一個自定義BelongsToManyThrough 關系，您可能會感興趣.您需要添加新的關系類(在我的要點中給出；粘貼在這里太長了)，并且還需要按照要點中的描述覆蓋您的基本 Model 類以實現 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(假設您使用 Laravel 的默認表命名方案 - 如果沒有，您也可以指定連接表)，您可以將關系定義為:

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 不僅會為您提供用戶的任務列表，還會告訴您每個用戶通過其擁有每個任務的角色.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()

輸出將類似于:

 [
    {
        "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."
            }
        ]
    }
]

我的自定義關系有效地完成了這項工作，只需要幾個查詢，而不是其他涉及 foreach 的解決方案，后者會創建一個 n+1 查詢 問題.

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.

這篇關于Laravel 5 雄辯的 hasManyThrough/belongsToManyThrough 關系的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！