Ruby Constant Lookup

Question

This is probably a simple question, but I'm trying to lookup the constant name in Ruby from the value. For example:

class Xyz < ActiveRecord::Base
  ACTIVE    = 1
  PENDING   = 2
  CANCELED  = 3
  SENT      = 4
  SUSPENDED = 5
end

I have a status of 1 in my db. I want to retrieve ACTIVE based on this so that I can display it in a view.

What's a good way to do that?

Answer 1

class Module
  def constant_by_value( val )
    constants.find{ |name| const_get(name)==val }
  end
end

class Xyz
  ACTIVE    = 1
  PENDING   = 2
  CANCELED  = 3
  SENT      = 4
  SUSPENDED = 5
end

p Xyz.constant_by_value(4)
#=> :SENT

However, I wouldn't do this: using programmatic names as values for a view seems like a bad idea. You're likely to run into a situation where you want to change the display name (maybe "suspended" should be shown as "on hold") and then you have to refactor your code.

I'd put a mapping in your view or controller, using the constants from the model:

status_name = {
  Xyz::ACTIVE    => "Active",
  Xyz::PENDING   => "Pending", 
  Xyz::CANCELED  => "Canceled", 
  Xyz::SENT      => "Away!", 
  Xyz::Suspended => "On Hold"
}
@status = status_name[@xyz.status_id]

Answer 2

I would put it into a constant array.

class xzy < ActiveRecord::Base
  STATUSES = %w{ACTIVE PENDING CANCELLED SENT SUSPENDED}

  def get_status
    STATUSES[self.status-1]
  end

  def get_status_id(name)
    STATUSES.index(name) + 1
  end
end

The minus 1 in #get_status and + 1 in #get_status_id are for zero-indexed arrays. I added the second method as I have found myself needing that from time to time.