Ruby ORMs

Abstract

Rails is really a collection of pieces that can be put together to create a web app. You can enhance or replace many of the components - how you write views, how controllers work, and how you build models. While models are built on top of ActiveRecord in the default Rails stack, you've got a lot of other choices.

In this presentation, we'll take a look at ActiveRecord and alternative ORMs. We'll discuss the pros and cons of each, and take a look at what the future will bring us.

ORMs

ActiveRecord
DataMapper
Sequel
ROM
Perpetuity
Mongoid
MongoMapper
Mince

ActiveRecord Pros

ActiveRecord is the 800-pount gorilla.

Ubiquitous
- Everyone knows it
- Lots of people improving on it
- Plugins usually assume you're using it
- Plenty of documentation
Well-tested
Well-understood
Super easy to get started
- It's included in Rails by default
ARel behind the scenes

ActiveRecord Cons

Class inheritance
- Not (current) idiomatic Ruby
- Prevents a hierarchical class structure
  - TODO: Show an example where this would be useful
Persistence and behavior in one class
- Violates SRP
- Makes testing harder and slower
  - TODO: Show examples of slow tests and fast test
Validations are also included (another responsibility)
No Identity Map
- TODO: Show example of where this is a problem
Have to look 2 places to find everything:
- Attributes (fields) are declared in the schema
- Relations are declared in the model itself

ActiveRecord Add-Ons

Includable ActiveRecord
- Solves the inheritance issue
Annotated Models (TODO: or its replacement)
- Kind of solves the problem of fields and relations in different places
Virtus::ActiveRecord or mini_record
- Solves the problem of fields and relations in different places
Squeel
- Gives a more Ruby-like API for scopes
Attachments (Paperclip, etc.)
Authentication (Devise, etc.)

DataMapper

Actually uses the Active Record pattern
Supports a lot more than just SQL on the back end
No further development (last updated 2012-08-27)

Sequel

Probably the best alternative right now
Good documentation
Leverages database features (like foreign key constraints)
Supports almost any SQL database you can think of
Thread safety, connection pooling
Awesome feature - set a model to a subset of a table:

DB = Sequel.connect('sqlite://blog.db')
class Post < Sequel::Model
  set_primary_key [:category, :title]
  set_dataset DB[:my_posts].where(category: 'ruby').select(:category, :title, :content).order(:date)
end

ROM

Should be the best alternative in the future
Previously was called DataMapper 2
- But has diverged a lot since the name change
Truly implements the Data Mapper pattern
Taking longer to get to 1.0 than hoped
- Developers seem to be low-level / bottom-up types
Supports in-memory (PostgreSQL in the works)
More pieces:
- Axiom
- ROM::Relation
- ROM::Mapper
- ROM::Session
- Model
Identity Map

Perpetuity

Worth looking at
Simple
Implements the Data Mapper patter
Supports MongoDB, PostgreSQL, in-memory
Identity Map

Mongoid and MongoMapper

See Sarah Mei's essay on why to avoid MongoDB in most cases
Mongoid
- Pretty simple
- Be sure to turn on MongoDB persistence!
- Pretty stable
TODO: Why to avoid MongoMapper

Mince

Simple and light-weight (no relations)
Supports MongoDB, Hashy (in-memory), and DynamoDB
Multi-tier architecture
- Collections and items
- Causes some un-DRYness declaring fields
No further development (last updated 2013-06-07)

	require 'mince'

	class BookDataModel
	  include Mince::DataModel
	  data_collection :books
	  data_fields :title, :publisher
	end

	class Book
	  include Mince::Model
	  data_model BookDataModel
	  fields :title, :publisher
	end

	book = Book.new title: 'The World In Photographs', publisher: 'National Geographic'
	book.save

Others

Swift
ORM Adapter
- Gives a standard API, sitting atop AR, DM, MM, or Mongoid

NoORM

POROs
Sometimes you don't need persistence for all your models
- TODO: Show examples
MagLev

The Future

ROM will reach 1.0 and be usable in production
Hopefully ROM will become the go-to ORM many cases
Perpetuity might become useful before ROM
MageLev might gather a following
Virtus::ActiveRecord might be a stepping-stone to ROM
ActiveRecord will continue to improve
We'll learn how to better use ActiveRecord

booch/Ruby ORMs.md