Are foreign keys really necessary in a database design?

Question

As far as I know, foreign keys (FK) are used to aid the programmer to manipulate data in the correct way. Suppose a programmer is actually doing this in the right manner alr

Answer 1

They are important, because your application is not the only way data can be manipulated in the database. Your application may handle referential integrity as honestly as it wants, but all it takes is one bozo with the right privileges to come along and issue an insert, delete or update command at the database level, and all your application referential integrity enforcement is bypassed. Putting FK constraints in at the database level means that, barring this bozo choosing to disable the FK constraint before issuing their command, the FK constraint will cause a bad insert/update/delete statement to fail with a referential integrity violation.