Define and use array of text values corresponding to numeric values

Question

I'm new to the Ruby on Rails environment, so I am stuck on what might be a simple question: I'm looking to define some text strings/labels that correspond to a numeric value. These values will be stored in the database and then used in my code instead of the numeric values.

In C, I would to something like this:

    #define Accounting  0
    #define Engineering 1
    #define Education   2

...to be used like this:

    if (field_of_study == Accounting) ...

I want to be able to do this in Rails controllers/views. I currently have to do something like this in my views to display items:

    <tr>
      <td><%= link_to user.name, user %></td>
      <% if user.studyField == 0 %>
        <td>Accounting</td>
      <% elsif user.studyField == 1 %>
        <td>Engineering</td>
      <% elsif user.studyField == 2 %>
        <td>Education</td>
      <% end %>
    </tr>

I would also like to use the text strings/labels in a drop-down menu in the form_for form and then save it using the numeric identifier. Do I need a before_save method to translate the two or is their an automatic way of doing this?

If I understand correctly, you could set up an Enumerable to do this. — 4444, Aug 02 '13 at 19:29
I completely understand how coming from a C environment, this would be your approach, but it's very un-ruby like. In ruby, you are more likely to use symbols like `:accounting :engineering :education` — Daiku, Aug 02 '13 at 20:08
Robert Reynolds - did one of the answers help you or do you have additional questions? If one of the answers meets your needs, can you please mark it as correct? Thanks. — Powers, Aug 04 '13 at 18:53

score 1 · Accepted Answer · edited May 23 '17 at 11:59

You might find this helpful: Ruby on Rails: Where to define global constants?.

In Rails, since all models are autoloaded by default, you might find it convenient to define your constants in the models, as follows

class User < ActiveRecord::Base
  ACCOUNTING = 0
  ENGINEERING = 1
  EDUCATION = 2
end

or even

class User < ActiveRecord::Base
  FIELDS = { accounting: 0, engineering: 1, education: 2 }
end

These can be used anywhere with User::ACCOUNTING or User::FIELDS[:accounting]. To use the second version inside a form, you can use

select('user', 'study_field', User::FIELDS)

Refer to select for more details.

This is what I was needing to understand in Ruby. Thanks for the help! — Robert Reynolds, Aug 07 '13 at 23:52

score 0 · Answer 2 · answered Aug 02 '13 at 19:33

There are a couple of ways to do this. You can assign the constants to integers and they should be saved to the database as integers:

# config/initializers/constants.rb
Accounting = 0
Engineering = 1

This is a bit ugly because Accounting is literally equal to zero. In Rails console:

Accounting == 0
=> true

However, this is probably the most straightforward way to meet your requirement and it looks like this is how your approached the problem with C.

Define and use array of text values corresponding to numeric values

2 Answers2