Question

Imagine this setup:

create table ObservationType 
(
ObservationTypeId int primary key identity(1,1),
Name nvarchar(32) not null
)

create table Observation
(
ObservationId int primary key identity(1,1),
ObservationTypeId int foreign key references ObservationType(ObservationTypeId),
Title nvarchar(32) not null,
Description nvarchar(1024) not null,
StudentId int foreign key references Student(StudentId)
)

create table Student
(
 foo bar
)

Now imagine this is full of data, it’s working fine. How do you deal when the user wants to delete an observation type? Do you automatically delete any observation that has that particular type as FK?

In the real world, how did you handle this situation?

Answer 1

In many cases, that’s the right thing to do – that’s why ON DELETE CASCADE exists.

This means that for the deleted row, any row in another table that is defined as such a foreign key on that row will also be deleted.

The question that you need to ask is whether it is something that the user will really want? Does it make sense within the application domain to perform such deletes? Ask your user/s what they expect to happen if they delete an observations type – what do they think should happen to the existing observations.

Sometimes, it is better to go with a soft delete (marking a row with a delete status in a status field), so you can recover/undelete. This is not without its share of problems.