Let’s have a model called Car and we want to keep information such as whether the car is rented, available or unavailable.
Let’s imagine that we added these fields to our table as follows.
class AddStatusesToCars < ActiveRecord::Migration def change add_column :cars, :rented, :boolean add_column :cars, :available, :boolean add_column :cars, :unavailable, :boolean endendAccording to this scenario, the car must be either rented,... read more
Let’s have a model called Car and we want to keep information such as whether the car is rented, available or unavailable.
Let’s imagine that we added these fields to our table as follows.
class AddStatusesToCars < ActiveRecord::Migration
def change
add_column :cars, :rented, :boolean
add_column :cars, :available, :boolean
add_column :cars, :unavailable, :boolean
end
end
According to this scenario, the car must be either rented, available or unavailable. It should not be both rented and available at the same time. We can handle this with validation. However, this time, when one is true, the other two columns will be empty. So let’s look at a way to do this in a single column:
class AddStatusToCars < ActiveRecord::Migration
def change
add_column :cars, :status, :integer, default: 0
end
end
class Car < ActiveRecord::Base
STATUSES = %w{rented available unavailable}
def status_to_s
STATUSES[status]
end
def available?
status_to_s == 'available'
end
def rented?
status_to_s == 'rented'
end
def unavailable?
status_to_s == 'unavailable'
end
end
Let’s look at its usage:
> Car.first.status_to_s
# => “available”
> Car.first.available?
# => true
> Car.first.rented?
# => false
> Car.first.unavailable?
# => false
This may be preferable instead of creating three columns. But, how do we solve the process of creating extra methods?
Let’s call the Enum into play.
Add the status field to our car model:
class AddStatusToCars < ActiveRecord::Migration
def change
add_column :cars, :status, :integer, default: 0
end
end
Define our statuses with enum in our car model.
class Book < ActiveRecord::Base
enum status: [:available, :rented, :unavailable]
# or define with number
# enum status: [
# available: 1,
# rented: 2,
# unavailable: 3
# ]
end
Let’s look at its usage:
> car = Car.first
> car.status
# => “available”
> car.rented?
# => false
# Change the car status to rented
car.status = :rented
car.rented! # updated
car.rented?
# => true
# To find all rented cars (scope method)
> Car.rented
# => SELECT "cars".* FROM "cars" WHERE "cars"."status" = ? [["status", 1]]
# [#<Car:0x007f41d3eeeeee
# id: 1,
# status: 1,
# ]
# To find all unavailable cars (scope method)
> Car.unavailable
# => SELECT "cars".* FROM "cars" WHERE "cars"."status" = ? [["status", 2]]
# => [] (There isn't any available car)
