Laravel save / update many to many relationship

eloquent, laravel, laravel-4, relationship

Solution

tldr; Use `sync` with 2nd param `false`

Many-to-many relationship is `belongsToMany` on both models:

// Task model
public function users()
{
  return $this->belongsToMany('User', 'user_tasks'); // assuming user_id and task_id as fk
}

// User model
public function tasks()
{
  return $this->belongsToMany('Task', 'user_tasks');
}

In order to add new relation use `attach` or `sync`.

Difference between the two is:

1 `attach` will add new row on the pivot table without checking if it's already there. It's good when you have additional data linked to that relation, for example:

`User` and `Exam` linked with pivot table `attempts: id, user_id, exam_id, score`

I suppose this is not what you need in your situation:

$user->tasks()->getRelatedIds(); // [1,2,3,4,5,6]

$user->tasks()->attach([5,6,7]);
// then
$user->tasks()->getRelatedIds(); // [1,2,3,4,5,6,5,6,7]

2 `sync` on the other hand, will either remove all relations and set them up anew:

$user->tasks()->getRelatedIds(); // [1,2,3,4,5,6]

$user->tasks()->sync([1,2,3]);
// then
$user->tasks()->getRelatedIds(); // [1,2,3]

or it will setup new relations without detaching previous AND without adding duplicates:

$user->tasks()->sync([5,6,7,8], false); // 2nd param = detach
// then
$user->tasks()->getRelatedIds(); // [1,2,3,4,5,6,7,8]

Problem

Can anyone help me on how to save many to many relationship? I have tasks, user can have many tasks and task can have many users (many to many), What I want to achieve is that in update form admin can assign multiple users to specific task. This is done through html multiple select input ``` name="taskParticipants[]" ``` The catch here is that through the same form (input) you can add/remove users, that's why I have to use sync(). Maybe I should start from the beginning but don't know where to start... This is my User model: ``` public function tasks() { return $this->belongsToMany('Task','user_tasks'); } ``` Task model ``` public function taskParticipants() { return $this->belongsToMany('User','user_tasks'); } ``` TaskController ``` public function update($task_id) { if (Input::has('taskParticipants')) { foreach(Input::get('taskParticipants') as $worker) { $task2 = $task->taskParticipants->toArray(); $task2 = array_add($task2,$task_id,$worker); $task->taskParticipants()->sync(array($task2)); } } } ``` This is structure of tables tasks id|title|deadline ``` user_tasks id|task_id|user_id ```

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