Laravel save / update many to many relationship

Question

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 

Answer 1

tldr; Use sync with 2nd param false

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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'); } 

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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] 

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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]