Good Bye Jacaranda and welcome ActiveRecord::Enum

Criado em: 29/12/2013

A time ago I want to create a Gem to learn how this works. But in the Ruby/Rails world we live in a mature community when we have a lot of libs to do our job, so I give up for a moment, until I have a problem that more people have experiencied too.

So in a moment I find a pattern, that I and my friends do. When I have a model, with validation of inclusion like this:

class Post < ActiveRecord::Base
  validates :status, inclusion: { in: %w{published unpublished draft} }
end

I normally need predicate methods like @post.published? and scopes like Post.published. So by this idea and some work born Jacaranda my first gem.

But now in the rails 4.1.0, I testing using 4.1.0.beta1 since no release yet. We have the ActiveRecord::Enum that can do the same thing we do with Jacaranda.

Meeting the ActiveRecord::Enum

Lets create the same behavior of Jacaranda now using the ActiveRecord::Enum.

Migration

We started with a migration like this.

class CreatePosts < ActiveRecord::Migration
  def change
    create_table :posts do |t|
      t.string :title
      t.integer :status, default: 0

      t.timestamps
    end
  end
end

The important part is the column is a integer and we set the default value as 0.

Model

In our model we simply use the macro enum.

class Post < ActiveRecord::Base

  enum status: %w(published unpublished draft)
end

In the Wild

Predicate methods

We start with a post with status is published. Remember you need to pass to the model the string and not integer, a ArgumentError is raised if you try pass the integer value.

Post.create(title: 'Post title', status: 'published')
post = Post.first
post.published? # true
post.draft? # false

Scopes

We can use the scopes with the same name as declareted on our model.

Post.published # SELECT "posts".* FROM "posts"  WHERE "posts"."status" = 0

Search is made using the integer value on the database.

The bang!

The bang are not in Jacaranda, but are cool =)

You can use the bang method to change the status of post.

post.draft!
post.status # "draft"

Now our post have the status as a draft.

One cool thing about the ActiveRecord::Enum is that all values are stored like a integer and accessed as a string.

Using explicit mapping

Add status without key can be annoying since if one new status is added in a wrong position all objects have values changed.

class Post < ActiveRecord::Base

  enum status: %w(reviewed published unpublished draft)
end

We add reviewed before the published, so now all published posts have the status as reviewed.

To avoid this problem, we can use the explicit mapping like.

class Post < ActiveRecord::Base

  enum status: { published: 0, unpublished: 1, draft: 2, reviwed: 3 }
end

This way we dont care about the order but with the value.

Of course good specs ensure we are adding a thing that dont break others.

Conclusion

Jacaranda is now deprecated, since we can use the ActiveRecord::Enum.

I learned a lot in the way using services like:

I used the Semantic Versioning. I learned how hard is the work to maintain a Gem. I started work in others open source projects. And is so enjoyable know that I was in the right direction =)

Groselhas