Laravel save / update many to many relationship

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]

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Here's my notes on how to save and update on all the Eloquent relationships.

in One to One:

You have to use HasOne on the first model and BelongsTo on the second model

to add record on the first model (HasOne) use the save function

example:    $post->comments()->save($comment);

to add record on the second model (BelongsTo) use the associate function

example:    $user->account()->associate($account);    $user->save();

in One to Many:

You have to use HasMany on the first model and BelongsTo on the second model

to add record on the first table (HasMany) use the save or saveMany functions

example:    $post->comments()->saveMany($comments);

to add record on the second model (BelongsTo) use the associate function

example:    $user->account()->associate($account);    $user->save();

in Many to Many:

You have to use BelongsToMany on the first model and BelongsToMany on the second model

to add records on the pivot table use attach or sync functions

both functions accepts single ID or array of ID’s

the difference is attach checks if the record already exist on the pivot table while sync don’t

example: $user->roles()->attach($roleId);

in Polymorphic One to Many:

You have to use MorphMany on the main model and MorphTo on all the (***able) models

to add records on all the other models use the save

example:    $course->tags()->save($tag);

the pivot table should have the following columns:

. main model ID

. (***able) ID

. (***able) Type

in Polymorphic Many to Many:

You have to use MorphByMany on the main model and MorphToMany on all the (***able) models

to add records on all the other models use the save or saveMany

example:    $course->tags()->save($tag);

example:    $course->tags()->saveMany([$tag_1, $tag_2, $tag_3]);

the pivot table should have the following columns:

. main model ID

. (***able) ID

. (***able) Type

in Has Many Through (shortcut):

You have to use HasManyThrough on the first table and have the normal relations on the other 2 tables

this doesn’t work for ManyToMany relationships (where there’s a pivot table)

however there’s a nice and easy solution just for that.

Here's an article I wrote, inspired by this answer. Important to check it: https://hackernoon.com/eloquent-relationships-cheat-sheet-5155498c209

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syncWithoutDetaching([$id_one, $id_two, $id_three]); is what you are looking for. Actually it does the exact thing [sync with 2nd param false] does!

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Solved: Use the updateOrInsert(array $attributes, array $values = [])

     DB::table('your_pivot_table')->updateOrInsert([
                'col' => $someValue
                

            ],[

                    'otherColumn' => $otherVlaue,
                   
                ]);
            

        }

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The sync function obliterates the exiting relationships and makes your array the entire list of relations. You want attach instead to add relations without removing others.

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for those who are searching for adding pivot attributes (the middle table attributes), you can use syncWithPivotValues and it also has the second parameter like this

$user->tasks()->syncWithPivotValues($tasksIDs,['day_number' => $day],false);

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