Retrieve distant relation through has-many-through for many-to-many relation in Laravel

问题

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?

回答1:

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();

回答2:

You can also take a look at the extension of the HasManyThrough here: https://github.com/staudenmeir/eloquent-has-many-deep

It helps you to retrieve many sub-levels of your relationships. In your case, it would be User -> belongsToMany(Groups) -> blongsToMany (Tasks) just add your method to the user model like:

public function tasks()
    {
        return $this->hasManyDeep(
            'App\Task',['App\Group']
        );
    }

来源：https://stackoverflow.com/questions/38138290/retrieve-distant-relation-through-has-many-through-for-many-to-many-relation-in

标签

php

laravel

eloquent

laravel-5.2