We'll respond shortly.
Let’s say you have a has_many relationship – project has_many stories. You don’t have dependent: destroy on the association.
If you call project.stories.delete_all, it does not delete the stories. Instead, it inserts NULL into the stories’ project_id field.
As a bonus, if the project_id field in the stories table has a not null constraint, then all of the project_ids become 0 – potentially attaching themselves to a completely different project.
delete_all works properly if the association has a dependent: destroy clause, and destroy_all works properly in either case.