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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?
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Rails validation defines valid states for each of your Active Record model classes. They are used to ensure that only valid details are entered into your database. Rails make it easy to add validations to your model classes and allows you to create your own validation methods as well.
Basically destroy runs any callbacks on the model while delete doesn't. Deletes the record in the database and freezes this instance to reflect that no changes should be made (since they can't be persisted). Returns the frozen instance.
Rails delete operation using destroy methodBy using destroy, you can delete the record from rails as well as its other existing dependencies. So in the context of our rails application, if we delete a book record using the destroy function, the authors associated with the book will also be deleted.
If you set the :dependent option to: :destroy, when the object is destroyed, destroy will be called on its associated objects. :delete, when the object is destroyed, all its associated objects will be deleted directly from the database without calling their destroy method.
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.
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