After destroy hook usage example for Sequel

gistfile1.rb

require 'sequel'
require 'sqlite3'

DB = Sequel.connect 'sqlite:/'

DB.create_table?(:people) do
  primary_key :id
  String :name
  foreign_key :address_id, :addresses
end

DB.create_table?(:addresses) do
  primary_key :id
  String :street
end

class Person < Sequel::Model
  many_to_one :address

  def after_destroy
    address.destroy if Person.where(address_id: address_id).empty?
  end
end

class Address < Sequel::Model
  one_to_many :people
end

address = Address.create(street: "Elm Street")
adam = Person.create(name: "Adam", address: address)
john = Person.create(name: "John", address: address)

puts "Before destroying people: #{Address.count}"

adam.destroy

puts "After destroying adam: #{Address.count}"

john.destroy

puts "After destroying john: #{Address.count}"


# Should output:
#
# Before destroying people: 1
# After destroying adam: 1
# After destroying john: 0

It's a real simple change, take this line out:

foreign_key :address_id, :addresses

and replace it with this one instead:

foreign_key :address_id, :addresses, null: false, on_delete: :cascade

Now every time you delete a parent object (Person), their addresses are mass-deleted automatically for you :) - it also has the added benefits of referential integrity

Thanks for the comment! :)

So, I applied your change but it did not work as intended:

Before destroying people: 1
After destroying adam: 1
After destroying john: 1

I guess it's because I do not want specifically to remove an address every time a person is deleted, I want to remove an address always when the last person that belonged to that address is deleted.

Oh I see. Addresses is not something I'd share between users, but I guess you were just illustrating the point, right? Even though, I'd rather use what I call a use case to encapsulate the person[+address] deletion process, at least that's how I see it now. Models are just for hitting the database, I strive to use regular ruby classes for implementing application-specific logic.

I have some good examples I'd like to bounce off you (and anyone else you'd like to listen). Please remind me to do so the next time we see each other :)

badosu was kindly helping me out, cristianrasch. As it happens, what he proposed works the way I had hoped.

As a parish minister, it works well for me to have addresses in a different table from people. The reason for that is that the addresses are generally geographically grouped into pastoral+administrative districts. It is often useful to know how many addresses are in a district as well as how many people are in a household. It is more helpful for my purpose to have a list of unique addresses for a district than to list multi-occupant addresses for each occupant.