Rails - Constants Hash?

Question

I have a need for a model(?) on my app which basically contains a status of another entity. In the entity I want to store the id of the status, but in my app, the view is talking in terms of a nice word description. For instance, 1=New, 2=Used etc etc.

How can I go about implementing this in the best way that means I can easily set and retrieve this status column without repeating myself?

Ultimately I would like something like

Foo.status = 'New'  (actually sets value to 1)

and

Foo.status  (returns 'New', but stores 1)

Am I even thinking about this in the right way?

Answer 1

You can code a custom writer method:

STATUS_VALUES = { 1 => 'new', 2 => 'modified', 3 => 'deleted' }

class Foo
  attr_reader :status_id

  def status
    STATUS_VALUES[@status_id]
  end

  def status=(new_value)
    @status_id = STATUS_VALUES.invert[new_value]
    new_value
  end
end

For example, the following program:

foo_1 = Foo.new

foo_1.status = 'new'
puts "status: #{foo_1.status}"
puts "status_id: #{foo_1.status_id}"

foo_1.status = 'deleted'
puts "status: #{foo_1.status}"
puts "status_id: #{foo_1.status_id}"

outputs:

status: new
status_id: 1
status: deleted
status_id: 3

Answer 2

One way could be using constants

module MyConstants
  New  = 1
  Used = 2
end

Then you can use them like this

Foo.status = MyConstants::New

or even like this if you're carefull about namespace polution

include MyConstants
Foo.status = New

On another thought, maybe you want to use a state machine.

Answer 3

I'd just go ahead and use symbols, something like

Foo.status = :new

They're basically immutable strings, meaning that no matter how many times you use the same symbol in your code, it's still one object in memory:

>> :new.object_id
=> 33538
>> :new.object_id
=> 33538
>> "new".object_id
=> 9035250
>> "new".object_id
=> 9029510 # <- Different object_id