Ruby on Rails and class variable confusion

Question

I have a model in Rails that has an enum attribute "status". I want to have a concept of public and private statuses, like so:

class Something < ActiveRecord::Base
  @public_statuses = [:open, :closed, :current]
  @private_statuses = [:deleted]

  enum status: @public_statuses + @private_statuses
end

So that I can do the following in a view:

<select>

<% Something.public_statuses.each do |status| %>
    <option value="<%= status %>"><%= status.humanize %></option>
<% end %>

</select>

This way, I don't expose the private statuses to the end user.

Unfortunately I don't understand Ruby classes very well and just cannot get this to work regardless of whether I do @public_statuses, @@public_statuses, public_statuses=[...] etc. I'm familiar with Java and other OO languages but just don't get what to do in Ruby here.

What is the right way to do this?

Tiago Farias · Accepted Answer · 2014-08-13 04:17:20Z

2

You can treat your variables like Class methods and define private the ones you don't want to be accessed (that's not absolutely true in Ruby). Like:

    def self.public_statuses
        [:open, :closed, :current]
    end

    def self.private_statuses
        [:deleted]
    end

    private_class_method :private_statuses

But if you really gonna go with variables, in this case, constants, it's very similar:

PUBLIC_STATUSES = [:open, :closed, :current]
PRIVATE_STATUSES = [:deleted]
private_constant :PRIVATE_STATUSES

So, you can use it:

puts Something::PUBLIC_STATUSES
=> [:open, :closed, :current]
puts Something::PRIVATE_STATUSES
NameError: private constant Client::PRIVATE_STATUSES referenced

edited Aug 13, 2014 at 4:17

answered Aug 13, 2014 at 4:11

Tiago Farias

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Comments

vee · Accepted Answer · 2014-08-13 04:24:31Z

What you've done is defined two instance variables not class variables so accessing them as Foo.instance_variable is not going to work. You need an instance of Foo to access them. So you'd replace your view each block with:

<% Something.new.public_statuses.each do |status| %>
  <option value="<%= status %>"><%= status.humanize %></option>
<% end %>

Here you instantiate Something then call pubic_statuses.each on that instance. So this will work for you.

However, if you'd like to use them as class variables then you need to add a class accessor method in your model class:

class Something < ActiveRecord::Base
  @@public_statuses = [:open, :closed, :current]
  @private_statuses = [:deleted]

  enum status: public_statuses + @private_statuses


  def self.public_statuses
    @@public_statuses
  end
end

As you are using Rails, you could also define a cattr_reader :public_statuses instead of the getter method defined in the code above. With these options of adding class method, you needn't change your view.

Another option is to make them constants:

class Something < ActiveRecord::Base
  PUBLIC_STATUSES = [:open, :closed, :current]
  PRIVATE_STATUSES = [:deleted]

  enum status: PUBLIC_STATUSES + PRIVATE_STATUSES
end

Then in your view:

<% Something::PUBLIC_STATUSES.each do |status| %>

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