Ardm

ActiveRecord plugin to provide a smooth migration from DataMapper to ActiveRecord.

Why

Ardm is intended for applications running Rails with DataMapper 1.2 who need to migrate to ActiveRecord. Lets examine some of the reasons why you might move to ActiveRecord.

• DataMapper is no longer under development. Ruby Object Mapper (ROM) is the imlicit replacement for DataMapper, but it's not a supported migration. ROM is a completely new codebase and very few of the idioms transfer.
• DataMapper produces inefficient queries. Includes, joins, and subqueries are either not supported or incorrect. Enabling subqueries in DM speeds up queries but causes other subtle query problems than can produce bad SQL that may select incorrect records.
• DataMapper cannot currently run on Rails4. Someone may take the initiative to upgrade DataMapper to work on Rails4, but I think you're much better off moving to ActiveRecord.
• Arel is awesome. ActiveRecord and Arel together is quite nice. With the added support properties and the advances in Rails4, I think this upgrade is a must.
• ActiveRecord is used in more applications, better tested, and more performant.

Installation

Incremental migration from DataMapper to ActiveRecord.

ActiveRecord requires your models to inherit from ActiveRecord::Base, but makes it difficult to approach the migration incrementally. All or nothing is a scary way to switch ORMs. To solve this, Ardm supplies Ardm::Record.

Ardm::Record will be the new base class. You'll need to search and replace all models that include DataMapper::Resource, remove it, and add Ardm::Record as the base class. If your model is STI, add it to the base model and remove DataMapper::Resource from all models.

Example:

class MyModel
  include DataMapper::Resource
  # ...
end

# The model above changes to:

class MyModel < Ardm::Record
  # ...
end

With this new base clase you can switch between ActiveRecord and DataMapper by flipping a swith in your application. This approach allows you to continue developing your application in DataMapper while you work on teasing out all the "datamapper-isms" from your code. This library attempts to take care of most DataMapper features, but there are probably tons of small variations that are not accounted for.

Usage

require 'ardm'

Copyright

This is an adaptation of the original DataMapper source code to allow users of the now defunct DataMapper to migrate to ActiveRecord. Much of this code was originally written by Sam Smoot and Dan Kubb as dm-types and dm-core. See LICENSE for details.