What is the difference between attach and sync in laravel

In Laravel, attach and sync are methods used for managing many-to-many relationships between models. While both are used to associate records in a pivot table, they serve different purposes. Here’s a detailed breakdown of the differences:

1. Attach

attach() method is used to add new entries to the pivot table without removing any existing ones. When we want to add a new relationship without altering any existing ones then we can use the attach() method.

use App\Models\User;

$user = User::find(1);

$user->roles()->attach([2, 3]);

This will add the roles with IDs 2 and 3 to the user_role pivot table. If the user already has roles (e.g., 1), those relationships will remain untouched.

2. Sync

sync() method in laravel synchronizes the pivot table by adding the specified relationships and removing any that are not in the list. It overwrites the existing relationships in the pivot table. This is used when we want to replace the current relationships with a new set of data.

use App\Models\User;

$user = User::find(1);

$user->roles()->sync([2, 3]);

This will ensure that the user has only the roles with IDs 2 and 3. If the user previously had roles (e.g., 1), that relationship will be removed.

Conclusion:

Use attach to add relationships incrementally. Use sync to replace the current relationships with a new set, ensuring no outdated relationships remain.