通过在拉拉维尔的多对多关系通过多元化交换获得遥远的关系 [英] Retrieve distant relation through has-many-through for many-to-many relation in Laravel

问题描述

我的应用程序中有以下型号

• 用户


• 组


• 任务

其中具有以下关系

• 用户和组具有多对多关系


• 任务和组具有多对多关系

所以基本上一个用户可以属于多个组，每个组可以有多个任务。

以下是表格结构。

用户

• id


• name

groups

• id


• 名称

任务

• id


• 名称

group_user

• id


• group_id（带有表的外键）


• user_id（带用户的外键s表）

group_tasks

• id


• group_id（带有表的外键）


• task_id（带有任务表的外键）

现在我想检索用户的所有任务。

我尝试了以下方法并且两者都不起作用。

方法1

• $ user-> groups（）给出用户的组列表


• $ group-> tasks（）给出组的任务列表

所以我尝试了

$ user-> groups（） - > tasks（）但没有起作用。 >

方法2

我尝试了有许多通过将其添加到我的用户模型中

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

但即使没有工作。以下是我得到的错误

  Connection.php行713中的QueryException：
 SQLSTATE [42S22]：列未找到：1054'字段列表'中的未知列'groups.user_id'（SQL：选择`tasks`。*，`groups`.`user_id从`tasks`内部连接`groups`在`groups`.`id `=`tasks`.`group_id`其中`groups`.`user_id` = 1）
  

我的猜测是这样的，因为它期待着一对多的关系，但是我有多对多关系。

那么有一种方法来检索

解决方案

 用户模型
 
 public function groups（）
 {
 return $ this-> belongsToMany（'App \Group'）; 
} 
 
组模型
 
 public function tasks（）
 {
 return $ this-> belongsToMany（'App \Task ）; 
} 
 
任务模型
 
 public function groups（）
 {
 return $ this-> belongsToMany（'App \Group ）; 
} 
  

检索用户的所有任务。

  $ user = User :: find（1）; 
 
 $ user-> load（'groups.tasks'）; 
 
 $ tasks = $ user-> groups-> pluck（'tasks'） - > collapse（）; 
  

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?

解决方案

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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