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? JavaScript questions and answers, JavaScript questions pdf, JavaScript question bank, JavaScript questions and answers pdf, mcq on JavaScript pdf, JavaScript questions and solutions, JavaScript mcq Test , Interview JavaScript questions, JavaScript Questions for Interview, JavaScript MCQ (Multiple Choice Questions)

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.