Establishing a relationship between two models through a Concern - ruby-on-rails

Question

I have the models Province and User and I need to stop a Province from being deleted if a User has that Province in it's address.
I can do User.province thanks to the following concern included in the model User:
module MyAddressable
extend ActiveSupport::Concern
included do
has_one :address, as: :addressable, dependent: :destroy
has_one :city, through: :address
has_one :province, through: :city
has_one :zone, through: :city
accepts_nested_attributes_for :address, reject_if: :reject_address, allow_destroy: true
end
end
I'm trying to establish the relationship between Province and User to be able to do something like Province.users, in the following way:
has_many :users, through: :myaddresable
With the following result:
ActiveRecord::HasManyThroughAssociationNotFoundError: Could not find the association :myaddresable in model Province
Same thing if I try to define the relationship as
has_many :users, through: :addressable
Can this be done? If so, what would be the right way to do it?

Answer 1

has_many :users, through: :addressable doesn't work because Province model has no knowledge about the Address model.
We can build the relationship between the Province model and User model through Address model.
The following setup works in rails 6
User Model
class User < ApplicationRecord
has_one :address, as: :addressable, dependent: :destroy
has_one :city, through: :address
has_one :province, through: :city
end
Province Model
class Province < ApplicationRecord
has_many :cities
has_many :users, through: :cities
end
City Model
class City < ApplicationRecord
has_many :addresses
has_many :users,
through: :addresses,
source: :addressable,
source_type: 'User'
belongs_to :province
end
Address Model
class Address < ApplicationRecord
belongs_to :addressable, polymorphic: true
belongs_to :city
end
Let's assume the migrations are defined correctly as per the model associations. Now the following queries work...
irb(main): > User.first.province
DEBUG -- : User Load (0.6ms) SELECT "users".* FROM "users" ORDER BY "users"."id" ASC LIMIT $1 [["LIMIT", 1]]
DEBUG -- : Province Load (0.3ms) SELECT "provinces".* FROM "provinces" INNER JOIN "cities" ON "provinces"."id" = "cities"."province_id" INNER JOIN "addresses" ON "cities"."id" = "addresses"."city_id" WHERE "addresses"."addressable_id" = $1 AND "addresses"."addressable_type" = $2 LIMIT $3 [["addressable_id", 1], ["addressable_type", "User"], ["LIMIT", 1]]
irb(main): > Province.first.users
DEBUG -- : Province Load (0.5ms) SELECT "provinces".* FROM "provinces" ORDER BY "provinces"."id" ASC LIMIT $1 [["LIMIT", 1]]
DEBUG -- : User Load (0.5ms) SELECT "users".* FROM "users" INNER JOIN "addresses" ON "users"."id" = "addresses"."addressable_id" INNER JOIN "cities" ON "addresses"."city_id" = "cities"."id" WHERE "cities"."province_id" = $1 AND "addresses"."addressable_type" = $2 [["province_id", 1], ["addressable_type", "User"]]
In your case, as the MyAddressable concern is already included in the User model, only the other associations and migrations need to be defined.
Hope this helps. Thank you.