How to use an Enum in Concern - ruby-on-rails

Question

I have this (simplified) concern:
module Nobi::Personable
extend ActiveSupport::Concern
included do
belongs_to :person, :autosave => true delegate :gender,
:gender=, :gender_changed?, :gender_was, :to => :person, :allow_nil => true
enum gender: { male: "male", female: "female" }
end
end
A Resident has this concern.
Now when I do this:
2.6.6> Resident.last.gender
Resident Load (16.2ms) SELECT "residents".* FROM "residents" ORDER BY "residents"."id" DESC LIMIT $1 [["LIMIT", 1]]
Person Load (16.1ms) SELECT "people".* FROM "people" WHERE "people"."id" = $1 LIMIT $2 [["id", 48], ["LIMIT", 1]]
=> "male"
However when I ask: male? I get:
2.6.6> Resident.last.male?
Resident Load (17.0ms) SELECT "residents".* FROM "residents" ORDER BY "residents"."id" DESC LIMIT $1 [["LIMIT", 1]]
=> false
How is this possible?
If I include the enum on the Person model, it works fine:
Person.last.male?
Person Load (15.9ms) SELECT "people".* FROM "people" ORDER BY "people"."id" DESC LIMIT $1 [["LIMIT", 1]]
=> true
I've created a minimalistic demo app which demonstrates this behavior:
https://github.com/rept/enum_app
r = Resident.create(gender: :male, local_gender: :local_male)
r.local_male?
=> true
r.male?
=> false

Answer 1

Declare an enum attribute where the values map to integers in the
database, but can be queried by name.
-- ActiveRecord::Enum
You either need to use an integer column with your enum or declare the mapping explicitly. Rails assumes that the values stored in the database are equal to the indices of the array passed to enum. Since "male" != 0 #male? will return false.
module Nobi::Personable
extend ActiveSupport::Concern
included do
belongs_to :person, :autosave => true
enum gender: {
male: "male",
female: "female"
}
end
end
While using a string column kind of defeats the point of using an enum in the first place declaring the mapping explicitly is seen as a best practice as it will prevent hard to debug breakages that can be caused by simply reordering the enum values in the array.
And if you need proof:
class User < ApplicationRecord
enum gender: [:male, :female] # users.gender is an integer column
end
irb(main):003:0> User.first
(0.9ms) SELECT sqlite_version(*)
User Load (2.0ms) SELECT "users".* FROM "users" ORDER BY "users"."id" ASC LIMIT ? [["LIMIT", 1]]
=> #<User id: 9, created_at: "2020-10-29 09:24:12", updated_at: "2020-10-29 09:24:12", gender: "male">
irb(main):004:0> User.first.male?
User Load (0.2ms) SELECT "users".* FROM "users" ORDER BY "users"."id" ASC LIMIT ? [["LIMIT", 1]]
=> true
class Resident < ApplicationRecord
# residents.gender is a string column
enum gender: {
male: 'male',
female: 'female'
}
end
irb(main):001:0> Resident.create!(gender: 'male')
(0.4ms) SELECT sqlite_version(*)
(0.1ms) begin transaction
Resident Create (1.6ms) INSERT INTO "residents" ("gender", "created_at", "updated_at") VALUES (?, ?, ?) [["gender", "male"], ["created_at", "2020-10-29 09:56:59.471917"], ["updated_at", "2020-10-29 09:56:59.471917"]]
(4.7ms) commit transaction
=> #<Resident id: 1, gender: "male", created_at: "2020-10-29 09:56:59", updated_at: "2020-10-29 09:56:59">
irb(main):002:0> Resident.first.male?
Resident Load (0.2ms) SELECT "residents".* FROM "residents" ORDER BY "residents"."id" ASC LIMIT ? [["LIMIT", 1]]
=> true