Synchronizing a one-to-many relationship

[inxty]

This is a common use case when we need to synchronize a one-to-many relationship.
For example when we have a Product model which contains a list of Specification

class Product extends Model {
    //...
    public function specifications() {
        return $this->hasMany(Specification:class);
    }
}

class Specification extends Model {
    //...
}

and the data in the specifications table

id | product_id | title       | value
10 | 42         | old title   | old val
20 | 42         | del title   | del val

and the specifications to save

$toSave = [
  [
    'id' => 10,
    'title' => 'Updated title',
    'value' => 'Updated value'
  ],
  [
    'id' => null,
    'title' => 'New title',
    'value' => 'New value'
  ]
];

currently we can synchronize the date by

$product = Product::find(42);

// Id of models we wish to keep
$toKeepIds = [10]; 

// deleting the unneeded elements
$product->specifications()->whereNotIn('id', $toKeepIds)->delete();

// update or create new elements
$product->specifications()->upsert(
    $toSave,       // Data to be created or updated
    ['id']             // Unique Id Column Key
);

It will be great to have such a method built-in the framework

public function sync($relation, $toSave) {
    //$toKeepIds = array_filter(array_map(function($elem) { return $elem['id']; }, $toSave));
    $toKeepIds = Arr::whereNotNull(Arr::pluck($toSave, 'id'));

    $this->$relation()->whereNotIn('id', $toKeepIds)->delete();

    $this->$relation()->upsert($toSave, ['id']);
}