What are the differences between attach, detach, and sync methods in Laravel

attach()

- The `attach()` method adds new records to the pivot table without affecting existing ones. It simply creates new associations between models.
- It is used when you want to incrementally add relationships without removing any current links.
- For example, if a user already has roles `[1,[2]` and you attach roles `[3][4]`, the resulting roles will be `[1,[2][3][4]`.
- It allows duplicates if you call attach multiple times with the same IDs (unless prevented by database constraints).
- Example usage:

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

This adds roles 2 and 3 to the user, keeping any existing roles intact[1][3][5].

detach()

- The `detach()` method removes records from the pivot table.
- It is used to delete relationships between models. You can detach specific IDs or all relationships.
- For example, `$user->roles()->detach([2])` removes role 2 from the user.
- Calling `$user->roles()->detach()` without arguments removes all roles from the user.
- It is useful for clearing or selectively removing relationships[6].

sync()

- The `sync()` method synchronizes the pivot table with the given list of IDs.
- It adds new relationships that are not currently attached and removes any existing relationships that are not in the given array.
- This means the pivot table will exactly match the array passed to `sync()`.
- For example, if a user has roles `[1][2][3]` and you call `$user->roles()->sync([2][4])`, the resulting roles will be `[2,[4]` - role 1 and 3 are removed, role 4 is added.
- This method is very useful when you want to replace the entire set of relationships with a new set.
- Laravel also provides `syncWithoutDetaching()` which adds new IDs without removing existing ones.
- Example usage:

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

This ensures the user only has roles 2 and 3, removing any others[1][3][5].

Summary of Differences

- attach(): Adds new pivot records without removing existing ones.
- detach(): Removes specified pivot records or all if no argument is provided.
- sync(): Replaces the current pivot records with the given array, adding new and removing old relationships as needed.

These methods provide flexible ways to manage many-to-many relationships in Laravel's Eloquent ORM, depending on whether you want to add, remove, or fully update related models in the pivot table.

Citations:
[1] https://stackoverflow.com/questions/23968415/laravel-eloquent-attach-vs-sync
[2] https://laravelmagazine.com/demystifying-the-attach-and-sync-methods-in-laravel-streamlining-many-to-many-relationships
[3] https://www.amitmerchant.com/attach-detach-sync-laravel/
[4] https://laracasts.com/discuss/channels/eloquent/confusion-related-to-sync-method
[5] https://krishna-bhandari.com.np/posts/what-is-the-difference-between-sync-and-attach-in-laravel/
[6] https://www.reddit.com/r/laravel/comments/gjw7h0/many_to_many_attach_working_but_not_detach/
[7] https://laravel.com/docs/11.x/eloquent-relationships
[8] https://laracasts.com/discuss/channels/eloquent/how-to-use-sync-eloquent-method