Laravel 8: how to manage Many-to-Many relationships with sync() method
If you’re using Laravel, you know that you can manage Many-to-Many relationships pretty easily.
An example of a many-to-many relationship is a library that has many best-seller books and those books are also shared by other libraries in the application.
So, a library has many books and a book has many libraries.
Usually, to define/manage the relationship between two resources, you can use the attach( ) method -to create the relationship- and the detach( ) method -to delete the Foreing Key Restraint-.
But Laravel also gives us a method called sync( ) to manage this type of relationship.
But what it does exactly? It syncronize the resources, automatically attaching the chosen ID’s and detaching the discarded ones.
It’s very easy to implement it:
It becomes very clear when using a <select> tag when creating a new Library resource.
With this result:
What will happen in the case above? In the pivot table book_library, the library resource will be attached with the selected book resources and the unselected will be detached.
In a resource update scenario, the relationships related to that specific resource would be updated (attached or detached) based on the selected/unselected items on the form.
To help manage this scenario, I’ll leave here a useful snippet to give a better visual feedback to the user:
With the if stated in the <option> tag, we’re usign the contains( ) method to check which books are related to the specific resource, to help the user for a better choice.