Should we write dependent: destroy on a join table model?

Question

I have 3 models A, B and C. B is the join table between A & C. The association is made through a has_many :through.

I was wondering if the non-join-table models (A & C in my case) should have dependent: :destroy with the join table association or if it's taken care automatically by rails ?

Is it the same answer for a HABTM association ?

Answer 1

No, because you can delete records without instantiating them which wouldn't call dependent destroy and you'd be left with orphaned records.

For example delete_all

Instead if you add a foreign key the database will handle the delete and it doesn't matter if you instantiate the object or not.

For example in a migration you can add

def change
  add_foreign_key :as, :bs, on_delete: :cascade
end

Or in the table creation migration

t.belongs_to :a, foreign_key: { on_delete: :cascade }