update or delete on table "service_registrations" violates foreign key constraint "fk_rails_afa9afc72b" on table code example
Example: PG::ForeignKeyViolation: ERROR: update or delete on table violates foreign key constraint
has_many :comments, dependent: :delete_all - just automatically delete them when the user is deleted
has_many :comments, dependent: :destroy - like above, but call
has_many :comments, dependent: :nullify - don't delete comments when the user is deleted, just null out their user_id column