问题描述
在Laravel 5.2应用程序中，我有三种模型： User ， Role 和 Task 。
一个用户与多个 Roles 和一个 Role 与多个 Tasks 相关联。
因此，每个用户通过其角色都与多个任务相关联。
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.
我正尝试访问所有 Tasks 通过其角色与用户关联。
I am trying to access all Tasks associated with a User, through their Roles.
我模型的相关部分如下：
The relevant parts of my models look like:
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；
The following returns an SQL error;
Column not found: 1054 Unknown column 'roles.user_id'
似乎正在尝试通过角色模型中的（不存在）外键而不是通过数据透视表访问关系。
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
我已经开发了，这可能会让您感兴趣。您将需要添加新的关系类（如我的要点所述；太长了，无法在此处粘贴），并且还按照要点中的描述覆盖了基础 Model 类来实现 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（假设您使用的是Laravel的默认表命名方案，如果没有，则可以指定以及联接表），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(
'App\Task',
'App\Role');
}
belongsToManyThrough 不会只会为您提供用户的任务列表，还会告诉您每个用户通过其执行每个任务的角色。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."
}
]
}
]
我的与涉及 foreach 的其他解决方案相比，自定义关系只需几个查询就能高效地完成此任务，而其他解决方案会创建问题。
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.
这篇关于Laravel 5雄辩的hasManyThrough / belongsToManyThrough关系的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！