before destroy call back

Question

I am a novice Ruby programmer working on a Rails API. I have a Location model and a User model, and a location has many users. They are related like this:

class Location << ActiveRecord::Base
  has_many: :users
end

class User << ActiveRecord::Base
  belongs_to :location
end

I want to put a constraint on the Location model so that a Location model object won't be destroyed if it has one or more associated Users.

Consider the case of Mumbai, which is a Location and it has one or more Users. As such, I cannot destroy that Location; I can destroy only if there are no users for a particular location.

How do to handle destroying records in a protected manner, such as this?

Answer 1

You can update your Location model to look like this:

class Location << ActiveRecord::Base
  before_destroy :confirm_safe_to_destroy

  has_many: :users

private

  def confirm_safe_to_destroy
    return false if users.any?
  end
end

This will use the before_destroy handler to check if it's safe to destroy the Location model object. The confirm_safe_to_destroy method returns false to halt the destroy process if there are any users associated with the location.