laravel pivot table with nullable foreign key

Question

I have a pivot table set up as follows:

user_roles
  user_id //fk->users.id
  assoc_id //nullable fk->association.id
  role //varchar

I set my database up this way because roles represent a many to many relationship: an association has many users, and a user may be in many associations. every user has a role within an association.

However, there are some roles that exist that can exist outside of an association. The database is configured to accept a null value in the assoc_id field and I can manually insert one from the command line, but when I attempt to execute

$user->roles()->attach(NULL, "outside contractor");

in my seed file, I get an error saying

[Illuminate\Database\QueryException]                                         
SQLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or update   
a child row: a foreign key constraint fails (`database`.`user_roles`, CONSTR  
AINT `user_roles_user_id_foreign` FOREIGN KEY (`user_id`) REFERENCES `users  
` (`id`)) (SQL: insert into `user_roles` () values ()) 

this is particularly confusing because shouldn't the first argument here be referring to the assoc_id? When I replace the NULL with a valid assoc_id,

$user->roles()->attach(1, "outside contractor");

the insert works fine, and the first argument refers to the assoc_id in the table.

What is going wrong?

Answer 1

If you don't provie a key/keys for attach/sync, Eloquent will not insert anything. It's rather expected behaviour, since what you are trying to do is:

Create a link between X and null

this is not what ORM is supposed to do.

Instead insert those rows manually:

$data = [
   'user_id' => 99, 
   'assoc_id' => null, 
   'role' => 'outside contractor'
];

DB::table('user_roles')->insert($data);