How to restrict values for a column

Question

I want to restrict available values for a field. So the value of the column must be from specified set of values. Is it possible using migration/models? Or I have to do it manually in my DB?

Answer 1

You'll use validations for this. There's a whole Rails guide on the topic. The specific helper you're looking for in this case is :inclusion, e.g.:

class Person < ActiveRecord::Base
  validates :relationship_status,
    :inclusion  => { :in => [ 'Single', 'Married', 'Divorced', 'Other' ],
    :message    => "%{value} is not a valid relationship status" }
end

Edit Aug. 2015: As of Rails 4.1, you can use the enum class method for this. It requires that your column be an integer type:

class Person < ActiveRecord::Base
  enum relationship_status: [ :single, :married, :divorced, :other ]
end

It automatically defines some handy methods for you, too:

p = Person.new(relationship_status: :married)

p.married? # => true
p.single? # => false

p.single!
p.single? # => true

You can read the documentation for enum here: http://api.rubyonrails.org/v4.1.0/classes/ActiveRecord/Enum.html

Answer 2

It depends on the amount of confidence you need. You could just add a validator to your model to restrict it to those values but then you wont be sure that existing data will match (and will cause subsequent saves to fail because of validation) and also that other changes could be made by other apps/raw sql that would get around it.

If you want absolute confidence, use the database.

Here's what you might want to use if you do it in the database (which is quite limited compared to what a rails validator could do: http://www.w3schools.com/sql/sql_check.asp