Quick Tip: Use Enums in Rails for Mapped Values

William Kennedy

When I worked in a call center, we used to mark cases with different statuses. This allowed upper management to get a handle on where cases stood, what the bottlenecks were and flow of calls. Thankfully it has been a long time since I worked in a call center, but I have pondered how I would accomplish this task with Rails. Thankfully, Rails has a solution known as Enums.

When you are adding statuses to a model, you might be tempted to use strings to set the status. This makes perfect sense because different statuses tend to be named things like ‘pending’, ‘under review’, and ‘completed’.

However, Rails encourages you to take advantage of Enums to replace these strings with integers. It seems counter-intuitive at first, but it is actually a perfect fit for the problem.

Enums allow you to map string values to integers in the database so they can be queried by name:

class CustomerCase < ApplicationRecord
  enum status: [:open, :closed,:under_review, :pending]

Now in the Rails console, we can do the following:

$ customer_case.open?

We can even use scopes:

$ CustomerCase.open

Just so we can really practice using Enums, I highly recommend creating a small Rails App:

$ rails new call_center

Change into that directory and generate a quick scaffold with lots of attributes:

$ rails generate scaffold CustomerCase title:string description:text status:integer agent:string

Notice that the status field is an integer.

Migrate the database:

$ rails db:migrate

Open up app/models/customer_case.rb and input the following:

class CustomerCase < ApplicationRecord
  enum status: [:open, :closed, :under_review, :pending]

Now we have a small application up and running. Go ahead and create a couple of cases yourself with different attributes in the rails console (rails c):

$ CustomerCase.create(title: "Case 1", description: "Our first case", status: :open, agent: "Me")
=> #<CustomerCase id: 1, title: "Case 1"...status: "open"
$ CustomerCase.create(title: "Case 2", description: "Our second case", status: :pending, agent: "Me")
=> #<CustomerCase id: 2, title: "Case 2"...status: "pending"

It’s also a good idea to change the line in app/views/customercase/form.html.erb that corresponds to the Enums so you can pick the actual statuses:

<div class="field">
  <%= f.label :status %><br>
  <%=  f.collection_select :status, CustomerCase.statuses.map{ |a| [a.first,a.first] },  :first, :second %>

I suggest creating as many different cases as possible and testing the different possibilities from the Rails console:

$ bundle exec rails c
$ cse = CustomerCase.create(title:"Case Title", description:"what has happend", status: "open" )
$ cse.open?
=> true
$ cse.closed?
=> false
$ cse.pending?
=> false
$ CustomerCase.open.to_a
CustomerCase Load (0.1ms)  SELECT "customer_cases".* FROM "customer_cases" WHERE "customer_cases"."status" = ?  [["status", 0]]
=> #<ActiveRecord::Relation..

The last example calling the open scope shows the SQL used to query the database. The query is using 0 for the value, not open, as expected.

You can also change the status of the case:

$ cse.pending!

(0.1ms) begin transaction
SQL (1.0ms) UPDATE “customercases” SET “status” = ?, “updatedat” = ? WHERE “customercases”.”id” = ? [[“status”, 3], [“updatedat”, 2016-10-05 13:34:28 UTC], [“id”, 3]]
(0.6ms) commit transaction
=> true

Enums, when used properly, can be a great addition to creating readable code. Now that we have explored Enums along with a possible use case, I hope that it will make implementing other Enum-related features into your Rails app easier.

CSS Master, 3rd Edition