I try to add a foreign key constraint in migrations. For some reason it does work when I set it to nullable, but it doesn't work when I make it not nullable. Why does this happen and how can I solve this?
This does work:
Schema::create('role_user', function (Blueprint $table){
$table->increments('id');
$table->integer('role_id')->unsigned()->index()->nullable();
$table->foreign('role_id')->references('id')->on('roles')->onDelete('set null');
$table->integer('user_id')->unsigned()->index()->nullable();
$table->foreign('user_id')->references('id')->on('users')->onDelete('set null');
$table->timestamps();
});
This throws the exception:
Schema::create('role_user', function (Blueprint $table){
$table->increments('id');
$table->integer('role_id')->unsigned()->index();
$table->foreign('role_id')->references('id')->on('roles')->onDelete('set null');
$table->integer('user_id')->unsigned()->index()->nullable();
$table->foreign('user_id')->references('id')->on('users')->onDelete('set null');
$table->timestamps();
});
Both the role and user tables already excist before making these constraints. I want them to be not nullable (so they must be filled). The error:
SQLSTATE[HY000]: General error: 1215 Cannot add foreign key constraint (SQL: alter table role_user add constraint role_user_role_id_foreign foreign key (role_id) references roles (id) on delete set null)
