通过Laravel中多对多关系的has-many-through检索远程关系

Question

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?

Answer 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();