Rails3: Defining enum and using it as a custom type for db column

Question

New to rails so not sure what the best approach is here. I want to define a simple c++ style enum which can then be used as a custom type in my db. The enum can be simulated with an array or a custom module but how do I go about turning that into a custom type for my table?

Answer 1

Have you considered using the built-in enumeration support in your database? Lots of common RDMBSes have enum support, such as Postgres (see http://www.postgresql.org/docs/9.1/static/datatype-enum.html) and MySQL (see http://dev.mysql.com/doc/refman/5.5/en/enum.html). With that, you can directly create the type in your data store and then use it via one of the ActiveRecord plugins (such as enum_type for Postgres: https://github.com/riscfuture/enum_type).

Alternatively, you could use something like active_enum to structure the enumeration as you described and store fields as integers in the database.

Answer 2

Here's a pattern I follow in rails:

In my model class, I add a module to hold the possible values of the column. Then I put them into an array and define validation against the array of possible values.

Imagine I have a column/attribute called status and it can be three possible values. I'd do this:

class MyModel < ActiveRecord::Base

  # This validates that status can't be null
  validates :status, :presence => true  

  # Define a module with all possible values
  module Status
    IN_DEVELOPMENT = 'in development'
    DISABLED = 'disabled'
    ACTIVE  = 'active'
  end

  # Now create an array of possible status values, and add a validation
  STATUSES = [ Status::DISABLED, Status::ACTIVE, Status::IN_DEVELOPMENT]
  validates :status, :inclusion => { :in => STATUSES, :message => "%{value} is not a valid status value" }

end

Answer 3

Depending on how you plan to utilize this enum type in your code I've found that using scopes accomplishes close to the same thing along with an enum type in the database to ensure only specific values are set.

Example:

scope :trial, :conditions => { :utype => 'TRIAL' }
scope :registered, :conditions => { :utype => 'REGISTERED' }
scope :active, :conditions => { :status => 'ACTIVE' }
scope :abuse, :conditions => { :status => 'ABUSE' }