如何在删除时处理 MySql + Laravel 中的外键约束？

Question

I have a slots table that looks something like this. Overly simplified, but it helps for demonstration:

Date	Service_id
2021-11-03	1
2021-11-04	2

Basically, a user picks a date and the service he wants. This is a booking system. There is also a foreign key relationship from service_id above to the id of the services table.

id	name
1	Haircut
2	Manicure
3	Massage

My migration for the slots table contains the following:

Schema::table('slots', function (Blueprint $table) {
     $table->foreignId('service_id')->nullable()->constrained();
});

What I want to do now is to be able to delete a service without having any errors being thrown from existing records in the slots table.

Answer 1

you can$table->nullOnDelete(); but this way the column Service_id in slots table should be nullable:

Schema::table('slots', function (Blueprint $table) {
     $table->foreignId('service_id')->nullable()->constrained()->nullOnDelete();
});

this way, the corresponding row in slots will have null in Service_id column.

the other way is to use ->cascadeOnDelete() , this way, when you delete a service, all related slots will be deleted:

 Schema::table('slots', function (Blueprint $table) {
         $table->foreignId('service_id')->nullable()->constrained()->cascadeOnDelete();
});