CouchRest Model: CouchDB, close to shiny metal with rounded edges

CouchRest Models adds additional functionality to the standard CouchRest Document class such as setting properties, callbacks, typecasting, and validations.

Originally called ExtendedDocument, the new Model structure uses ActiveModel, part of Rails 3, for validations and callbacks.

If your project is still running Rails 2.3, you'll have to continue using ExtendedDocument as it is not possible to load ActiveModel into programs that do not use ActiveSupport 3.0.

CouchRest Model only supports CouchDB 0.10.0 or newer.

Install

From Gem

CouchRest Model depends on Rails 3's ActiveModel which has not yet been released. You'll need to add --pre to the end of the gem install until the dependencies are stable:

$ sudo gem install couchrest_model --pre

Bundler

If you're using bundler, just define a line similar to the following in your project's Gemfile:

gem 'couchrest_model'

You might also consider using the latest git repository. All tests should pass in the master code branch but no guarantees!

gem 'couchrest_model', :git => 'git://github.com/couchrest/couchrest_model.git'

General Usage

require 'couchrest_model'

class Cat < CouchRest::Model::Base

  property :name,      String
  property :lives,     Integer, :default => 9

  property :nicknames, [String]

  timestamps!

  view_by :name

end

@cat = Cat.new(:name => 'Felix', :nicknames => ['so cute', 'sweet kitty'])

@cat.new?   # true
@cat.save

@cat['name']   # "Felix"

@cat.nicknames << 'getoffdamntable'

@cat = Cat.new
@cat.update_attributes(:name => 'Felix', :random_text => 'feline')
@cat.new? # false
@cat.random_text  # Raises error!

Properties

Only attributes with a property definition will be stored be CouchRest Model (as opposed to a normal CouchRest Document which will store everything). To help prevent confusion, a property should be considered as the definition of an attribute. An attribute must be associated with a property, but a property may not have any attributes associated if none have been set.

In its simplest form, a property will only create a getter and setter passing all attribute data directly to the database. Assuming the attribute provided responds to to_json, there will not be any problems saving it, but when loading the data back it will either be a string, number, array, or hash:

class Cat < CouchRest::Model::Base
  property :name
  property :birthday
end

@cat = Cat.new(:name => 'Felix', :birthday => 2.years.ago)
@cat.name        # 'Felix'
@cat.birthday.is_a?(Time)  # True!
@cat.save
@cat = Cat.find(@cat.id)
@cat.name        # 'Felix'
@cat.birthday.is_a?(Time)  # False!

Properties create getters and setters similar to the following:

def name
  read_attribute('name')
end

def name=(value)
  write_attribute('name', value)
end

Properties can also have a type which will be used for casting data retrieved from CouchDB when the attribute is set:

class Cat < CouchRest::Model::Base
  property :name, String
  property :last_fed_at, Time
end

@cat = Cat.new(:name => 'Felix', :last_fed_at => 10.minutes.ago)
@cat.last_fed_at.is_a?(Time)   # True!
@cat.save
@cat = Cat.find(@cat.id)
@cat.last_fed_at < 20.minutes.ago   # True!

Booleans or TrueClass will also create a getter with question mark at the end:

class Cat < CouchRest::Model::Base
  property :awake, TrueClass, :default => true
end

@cat.awake?   # true

Adding the +:default+ option will ensure the attribute always has a value.

Defining a property as read-only will mean that its value is set only when read from the database and that it will not have a setter method. You can however update a read-only attribute using the write_attribute method:

class Cat < CouchRest::Model::Base
  property :name, String
  property :lives, Integer, :default => 9, :readonly => true  

  def fall_off_balcony!
    write_attribute(:lives, lives - 1)
    save
  end
end

@cat = Cat.new(:name => "Felix")
@cat.fall_off_balcony!
@cat.lives    # Now 8!

Property Arrays

An attribute may also contain an array of data. CouchRest Model handles this, along with casting, by defining the class of the child attributes inside an Array:

class Cat < CouchRest::Model::Base
  property :name, String
  property :nicknames, [String]
end

By default, the array will be ready to use from the moment the object as been instantiated:

@cat = Cat.new(:name => 'Fluffy')
@cat.nicknames << 'Buffy'

@cat.nicknames == ['Buffy']

When anything other than a string is set as the class of a property, the array will be converted into special wrapper called a CastedArray. If the child objects respond to the casted_by method (such as those created with CastedModel, below) it will contain a reference to the parent.

Casted Models

CouchRest Model allows you to take full advantage of CouchDB's ability to store complex documents and retrieve them using the CastedModel module. Simply include the module in a Hash (or other model that responds to the [] and []= methods) and set any properties you'd like to use. For example:

class CatToy << Hash
  include CouchRest::Model::CastedModel

  property :name, String
  property :purchased, Date
end

class Cat << CouchRest::Model::Base
  property :name, String
  property :toys, [CatToy]
end

@cat = Cat.new(:name => 'Felix', :toys => [{:name => 'mouse', :purchases => 1.month.ago}])
@cat.toys.first.class == CatToy
@cat.toys.first.name == 'mouse'

Additionally, any hashes sent to the property will automatically be converted:

@cat.toys << {:name => 'catnip ball'}
@cat.toys.last.is_a?(CatToy) # True!

Of course, to use your own classes they must be defined before the parent uses them otherwise Ruby will bring up a missing constant error. To avoid this, or if you have a really simple array of data you'd like to model, the latest version of CouchRest Model (> 1.0.0) supports creating anonymous classes:

class Cat << CouchRest::Model::Base
  property :name, String

  property :toys do |toy|
    toy.property :name, String
    toy.property :rating, Integer
  end
end

@cat = Cat.new(:name => 'Felix', :toys => [{:name => 'mouse', :rating => 3}, {:name => 'catnip ball', :rating => 5}])
@cat.toys.last.rating == 5
@cat.toys.last.name == 'catnip ball'

Using this method of anonymous classes will only create arrays of objects.

Assocations

Two types at the moment:

belongs_to :person

collection_of :tags

TODO: Document properly!

Validations

CouchRest Model automatically includes the new ActiveModel validations, so they should work just as the traditional Rails validations. For more details, please see the ActiveModel::Validations documentation.

CouchRest Model adds the possibility to check the uniqueness of attributes using the validates_uniqueness_of class method, for example:

class Person < CouchRest::Model::Base
  property :title, String
 
  validates_uniqueness_of :title
end

The uniqueness validation creates a new view for the attribute or uses one that already exists. You can specify a different view using the :view option, useful for when the unique_id is specified and you'd like to avoid the typical RestClient Conflict error:

unique_id :code
validates_uniqueness_of :code, :view => 'all'

Given that the uniqueness check performs a request to the database, it is also possible to include a @:proxy@ parameter. This allows you to call a method on the document and provide an alternate proxy object.

Examples:

# Same as not including proxy:
validates_uniqueness_of :title, :proxy => 'class'

# Person#company.people provides a proxy object for people
validates_uniqueness_of :title, :proxy => 'company.people'

A really interesting use of +:proxy+ and +:view+ together could be where you'd like to ensure the ID is unique between several types of document. For example:

class Product < CouchRest::Model::Base
  property :code

  validates_uniqueness_of :code, :view => 'by_product_code'

  view_by :product_code, :map => "
    function(doc) {
      if (doc['couchrest-type'] == 'Product' || doc['couchrest-type'] == 'Project') {
        emit(doc['code']);
      }
    }
  "
end

class Project < CouchRest::Model::Base
  property :code

  validates_uniqueness_of :code, :view => 'by_product_code', :proxy => 'Product'
end

Pretty cool!

Notable Issues

CouchRest Model uses active_support for some of its internals. Ensure you have a stable active support gem installed or at least 3.0.0.beta4.

JSON gem versions 1.4.X are kown to cause problems with stack overflows and general badness. Version 1.2.4 appears to work fine.

Ruby on Rails

CouchRest Model is compatible with rails and provides some ActiveRecord-like methods.

The CouchRest companion rails project http://github.com/hpoydar/couchrest-rails is great for provided default connection details for your database. At the time of writting however it does not provide explicit support for CouchRest Model.

CouchRest Model and the original CouchRest ExtendedDocument do not share the same namespace, as such you should not have any problems using them both at the same time. This might help with migrations.

Rails 3.0

In your Gemfile require the gem with a simple line:

gem "couchrest_model"

Testing

The most complete documentation is the spec/ directory. To validate your CouchRest install, from the project root directory run rake, or autotest (requires RSpec and optionally ZenTest for autotest support).

Docs

API: http://rdoc.info/projects/couchrest/couchrest_model

Check the wiki for documentation and examples http://wiki.github.com/couchrest/couchrest_model

Contact

Please post bugs, suggestions and patches to the bug tracker at http://github.com/couchrest/couchrest_model/issues.

Follow us on Twitter: http://twitter.com/couchrest

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