---
title: Refactoring From Model to View Helper to Null Object
teaser:
tags: web,rails,ruby,upcase
author: Tute Costa
published_on: 2014-10-10
---

We are working to add more thorough progress tracking to
[upcase.com](https://thoughtbot.com/upcase/?utm_source=giant-robots-blog).

Chad and I were pairing on the backend for this feature, and we created a model
called `Status`, that belongs both to a `User` and to an `Exercise`. This is a
many-to-many relationship that holds a `state` attribute. That way we can query,
for each exercise, what its `state` is for the currently signed in user.

![''](https://images.thoughtbot.com/upcase-refactor-post/upcase-statuses.png)

When a user starts an exercise, we create a `Status` object, with a `state` of
`"Started"`. If there is no related `Status`, then the exercise was not yet
started (and we display to the user `"Not Started"`).

## Initial Implementation: Model method

Initially we implemented the following method in the `Exercise` model:

```ruby
class Exercise < ActiveRecord::Base
  def state_for(user)
    if status = status_for(user)
      status.state
    else
      "Not Started"
    end
  end

  def status_for(user)
    statuses.where(user: user).order(:created_at).last
  end
end
```

This made the tests green, and now it was time to refactor. The model was
responsible of knowing what to display in the view for an exercise that was not
started (the `"Not Started"` string). This was obvious while writing tests. We
moved from integration into unit tests, and discovered we were asserting the
label shown to the user inside of the model spec.

## First Refactoring: View Helpers

We felt this belonged to the View layer, and moved the method into a helper:

```ruby
module ExercisesHelper
  def state_for(user:, exercise:)
    if status = exercise.status_for(user)
      status.state
    else
      "Not Started"
    end
  end
end
```

At this point, Chad and I pushed up our latest changes and opened a pull
request. The feedback we received provided us with an even better solution:

![''](https://images.thoughtbot.com/upcase-refactor-post/null-object-comment.png)

## Second Refactoring: Null Objects

The helper's conditional decides what is the `state` for a `Status` that doesn't
yet exist. The `state` of a `NullStatus`. We chose to name this null object
`NotStarted` because it makes explicit _why_ we need it, rather than just
denoting _what_ it is.

The third and best implementation we found is:

```ruby
class NotStarted
  def state
    "Not Started"
  end
end

class Exercise < ActiveRecord::Base
  def status_for(user)
    statuses.where(user: user).order(:created_at).last || NotStarted.new
  end
end
```

In the view we always show `state`, and the corresponding object will always
tell us:

```erb
<%= exercise.status_for(current_user).state %>
```

We [Replaced Conditional with
Polymorphism](https://thoughtbot.com/blog/refactoring-replace-conditional-with-polymorphism).
No wonder the reviewer was also the author of the Polymorphism blog post, thank
you Joe! Thank you twice.

## What's next

Upcase subscribers get access to the [Upcase GitHub
repo](https://thoughtbot.com/upcase/upcase-repo?utm_source=giant-robots-blog), where they
are welcome to see all new features, improvements, and refactorings as we make
them.

If you already have access, you may check the pull request with the whole
discussion (PR #914). Otherwise, you can always get access to this and more
thoughtbot content and repositories through
[Upcase](https://thoughtbot.com/upcase/subscription/new?utm_source=giant-robots-blog).

Enjoy!