ActiveRecord outside Rails

It’s possible to use ActiveRecord to handle or test persistence, outside a Rails project. You can generate models, migrate and write specs just by using the AR gem.

And why would you ever want to use AR outside Rails? In my case, I am writing a gem which needs to parse models to generate schema structures and want to write specs within the gem to test for persistence.

There are blogs and gems dedicated to address this topic like:

• http://journal.dedasys.com/2007/01/28/using-migrations-outside-of-rails
• https://github.com/thuss/standalone-migrations
• http://blog.aizatto.com/2007/05/21/activerecord-without-rails/

The steps are pretty simple:

1. Use ActiveRecord gem

gem.add_dependency  "activerecord", "~> 3.2.0" #if using in a gem

gem "activerecord", "~> 3.2.0" #in Gemfile for all other cases

 

2. Write/Generate a Migration

The simplest migration looks like this:

  class CreatePosts < ActiveRecord::Migration
    def self.up
      create_table :posts, :force => true do |t|
        t.timestamps
      end
    end
    def self.down
      drop_table :yetis
    end
  end

 

You can either hand-code this block (Textmate, for one, has a pretty good Ruby-on-Rails bundle to support this) or you code use a gem like standalone-migrations to generate the model.

3. Establish a database connection

SQLite serves well to create a database on the fly:

ActiveRecord::Base.establish_connection adapter: "sqlite3", database: "db/testdb"

 

You can also create a database.yml and pass it as a parameter to establish_connection. A standard database.yml looks like:

adapter: mysql
database: database
username: user
password: password
host: localhost

 

To load the database.yml:

require 'yaml'

dbconfig = YAML::load(File.open('database.yml'))
ActiveRecord::Base.establish_connection(dbconfig)

 

4. Migrate to database

Use ActiveRecord::Migrator to generate the actual table in your database. If your migrations are present in a folder like schema/migrations, then:

ActiveRecord::Migrator.migrate("../schema/migrations")

 

5. Write a Test

describe "Post" do
  it "checks if Post is really an ActiveRecord::Base class" do
    Post.superclass.name.should eq "ActiveRecord::Base"
  end
end

 

This should return a success.