How do I 'validate' on destroy in rails

Question

On destruction of a restful resource, I want to guarantee a few things before I allow a destroy operation to continue? Basically, I want the ability to stop the destroy operation if I note that doing so would place the database in a invalid state? There are no validation callbacks on a destroy operation, so how does one "validate" whether a destroy operation should be accepted?

Answer 1

You can raise an exception which you then catch. Rails wraps deletes in a transaction, which helps matters.

For example:

class Booking < ActiveRecord::Base   has_many   :booking_payments   ....   def destroy     raise "Cannot delete booking with payments" unless booking_payments.count == 0     # ... ok, go ahead and destroy     super   end end 

Alternatively you can use the before_destroy callback. This callback is normally used to destroy dependent records, but you can throw an exception or add an error instead.

def before_destroy   return true if booking_payments.count == 0   errors.add :base, "Cannot delete booking with payments"   # or errors.add_to_base in Rails 2   false   # Rails 5   throw(:abort) end 

myBooking.destroy will now return false, and myBooking.errors will be populated on return.