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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 is only properly tested on CouchDB version 1.0 or newer.

WARNING: As of April 2011 and the release of version 1.1.0, the default model type key is 'model' instead of 'couchrest-type'. Simply updating your project will not work unless you migrate your data or set the configuration option in your initializers:

CouchRest::Model::Base.configure do |config|
  config.model_type_key = 'couchrest-type'

This is because CouchRest Model's are not couchrest specific and may be used in any other system such as a Javascript library, the model type should reflect this.



$ sudo gem install couchrest_model


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

gem 'couchrest_model'

You might also consider using the latest git repository. We try to make sure the current version in git is stable and at the very least all tests should pass.

gem 'couchrest_model', :git => 'git://'


There is currently no standard way for telling CouchRest Model how it should access your database, this is something we're still working on. For the time being, the easiest way is to set a COUCHDB_DATABASE global variable to an instance of CouchRest Database, and call use_database COUCHDB_DATABASE in each model.

TODO: Add an example!


CouchRest Model now comes with a Gemfile to help with development. If you want to make changes to the code, download a copy then run:

bundle install

That should set everything up for rake spec to be run correctly. Update the couchrest_model.gemspec if your alterations use different gems.



    $ rails generate model person --orm=couchrest_model

Useful links and extensions

Try some of these gems that add extra funcionality to couchrest_model:

  • memories - object versioning using attachments (Matt Parker)
  • couch_publish - versioned state machine for draft and published documents (Matt Parker)
  • couch_photo - attach images to documents with variations (Matt Parker)
  • copycouch - single document replication on documents (Matt Parker)
  • recloner - clone documents easily (Matt Parker)
  • couchrest_localised_properties - Transparent support for localised properties (Sam Lown)

If you have an extension that you'd us to add to this list, please get in touch!

General Usage

require 'couchrest_model'

class Cat < CouchRest::Model::Base

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

  property :nicknames, [String]


  view_by :name


@cat = => 'Felix', :nicknames => ['so cute', 'sweet kitty'])   # true

@cat['name']   # "Felix"

@cat.nicknames << 'getoffdamntable'

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


A property is the definition of an attribute, it describes what the attribute is called, how it should be type casted and other options such as the default value. These replace your typical add_column methods found in relational database migrations.

Attributes with a property definition will have setter and getter methods defined for them. Any other attibute can be set as if the model were a Hash, this funcionality is inherited from CouchRest Documents.

Here are a few examples of the way properties are used:

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

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

Properties create getters and setters similar to the following:

def name

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

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

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

Boolean or TrueClass types will create a getter with question mark at the end:

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

@cat.awake?   # true

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

A read-only property will only have a getter method, and its value is set when the document is read from the database. 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)

@cat = => "Felix")
@cat.lives    # Now 8!

Mass assigning attributes is also possible in a similar fashion to ActiveRecord:

@cat.attributes = { :name => "Felix" }

Is the same as:

@cat.update_attributes(:name => "Felix")

By default, attributes without a property will not be updated via the #attributes= method. This provents useless data being passed to database, for example from an HTML form. However, if you would like truely dynamic attributes, the mass_assign_any_attribute configuration option when set to true will store everything you put into the Base#attributes= method.

Property Arrays

An attribute may 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]

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

@cat = => '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

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

@cat = => 'Felix', :toys => [{:name => 'mouse', :purchased => 1.month.ago}]) == CatToy == 'mouse'

Any hashes sent to the property will automatically be converted: << {:name => 'catnip ball'} # True!

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, CouchRest Model supports creating anonymous classes:

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

  property :toys do
    property :name, String
    property :rating, Integer

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

Anonymous classes will only create arrays of objects. If you're more of the traditional type, a block parameter can be provided allowing you to use this variable before each method call inside the anonymous class. This is useful if you need to access variables outside of the block.


CouchDB views can be quite difficult to get grips with at first as they are quite different from what you'd expect with SQL queries in a normal Relational Database. Checkout some of the CouchDB documentation on views to get to grips with the basics. The key is to remember that CouchDB will only generate indexes from which you can extract consecutive rows of data, filtering other than between two points in a data set is not possible.

CouchRest Model has great support for views, and since version 1.1.0 we added support for a View objects that make accessing your data even easier.

The Old Way

Here's an example of adding a view to our Cat class:

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

  view_by :name

The view_by method will create a view in the Cat's design document called "by_name". This will allow searches to be made for the Cat's name attribute. Calling Cat.by_name will send a query of to the database and return an array of all the Cat objects available. Internally, a map function is generated automatically and stored in CouchDB's design document for the current model, it'll look something like the following:

function(doc) {
  if (doc['couchrest-type'] == 'Cat' && doc['name']) {
    emit(, null);

By default, a special view called all is created and added to all couchrest models that allows you access to all the documents in the database that match the model. By default, these will be ordered by each documents id field.

It is also possible to create views of multiple keys, for example:

view_by :birthday, :name

This will create an view of all the cats' birthdays and their names called by_birthday_and_name.

Sometimes the automatically generate map function might not be sufficient for more complicated queries. To customize, add the :map and :reduce functions when creating the view:

view_by :tags,
  :map =>
    "function(doc) {
      if (doc['model'] == 'Post' && doc.tags) {
          emit(doc.tag, 1);
  :reduce =>
    "function(keys, values, rereduce) {
      return sum(values);

Calling a view will return document objects by default, to get access to the raw CouchDB result add the :raw => true option to get a hash instead. Custom views can also be queried with :reduce => true to return reduce results. The default is to query with :reduce => false.

Views are generated (on a per-model basis) lazily on first-access. This means that if you are deploying changes to a view, the views for that model won't be available until generation is complete. This can take some time with large databases. Strategies are in the works.

View Objects

Since CouchRest Model 1.1.0 it is now possible to create views that return objects chainable objects, similar to those you'd find in the Sequel Ruby library or Rails 3's Arel. Heres an example of creating a few views:

class Post < CouchRest::Model::Base
  property :title
  property :body
  property :posted_at, DateTime
  property :tags, [String]

  design do
    view :by_title
    view :by_posted_at_and_title
    view :tag_list,
      :map =>
        "function(doc) {
          if (doc['model'] == 'Post' && doc.tags) {
              emit(doc.tag, 1);
      :reduce =>
        "function(keys, values, rereduce) {
          return sum(values);

You'll see that this new syntax requires all views to be defined inside a design block. Unlike the old version, the keys to be used in a query are determined from the name of the view, not the other way round. Acessing data is the fun part:

# Prepare a query:
view = Post.by_posted_at_and_title.skip(5).limit(10)

# Fetch the results:
view.each do |post|
  puts "Title: #{post.title}"

# Grab the CouchDB result information with the same object:
view.total_rows   => 10
view.offset       => 5

# Re-use and add new filters
filter = view.startkey([1.month.ago]).endkey([Date.current, {}])

# Fetch row results without the documents:
filter.rows.each do |row|
  puts "Row value: #{row.value} Doc ID: #{}"

# Lazily load documents (take last row from previous example):
row.doc      => Fetch last Post document from database

# Using reduced queries is also easy:
tag_usage = Post.tag_list.reduce.group_level(1)
tag_usage.rows.each do |row|
  puts "Tag: #{row.key}  Uses: #{row.value}"


The view objects have built in support for pagination based on the kaminari gem. Methods are provided to match those required by the library to peform pagination.

For your view to support paginating the results, it must use a reduce function that provides a total count of the documents in the result set. By default, auto-generated views include a reduce function that supports this.

Use pagination as follows:

# Prepare a query:
@posts =[:page]).per(10)

# In your view, with the kaminari gem loaded:
paginate @posts

Design Documents and Views

Views must be defined in a Design Document for CouchDB to be able to perform searches. Each model therefore must have its own Design Document. Deciding when to update the model's design doc is a difficult issue, as in production you don't want to be constantly checking for updates and in development maximum flexability is important. CouchRest Model solves this issue by providing the auto_update_design_doc configuration option and is true by default.

Each time a view or other design method is requested a quick GET for the design will be sent to ensure it is up to date with the latest changes. Results are cached in the current thread for the complete design document's URL, including the database, to try and limit requests. This should be fine for most projects, but dealing with multiple sub-databases may require a different strategy.

Setting the option to false will require a manual update of each model's design doc whenever you know a change has happened. This will be useful in cases when you do not want CouchRest Model to interfere with the views already store in the CouchRest database, or you'd like to deploy your own update strategy. Here's an example of a module that will update all submodules:

module CouchRestMigration
  def self.update_design_docs
    CouchRest::Model::Base.subclasses.each{|klass| klass.save_design_doc! if klass.respond_to?(:save_design_doc!)}

# Running this from your applications initializers would be a good idea,
# for example in Rail's application.rb or environments/production.rb:
config.after_initialize do

If you're dealing with multiple databases, using proxied models, or databases that are created on-the-fly, a more sophisticated approach might be required:

module CouchRestMigration
  def self.update_all_design_docs
    Company.all.each do |company|
  def self.update_design_docs(db)
    CouchRest::Model::Base.subclasses.each{|klass| klass.save_design_doc!(db) if klass.respond_to?(:save_design_doc!}

# Command to run after a capistrano migration:
$ rails runner "CouchRestMigratin.update_all_design_docs"


Two types at the moment:

belongs_to :person

collection_of :tags

This is a somewhat controvesial feature of CouchRest Model that some document database purists may cringe at. CouchDB does not yet povide many features to support relationships between documents but the fact of that matter is that its a very useful paradigm for modelling data systems.

In the near future we hope to add support for a has_many relationship that takes of the Linked Documents feature that arrived in CouchDB 0.11.

Belongs To

Creates a property in the document with _id added to the end of the name of the foreign model with getter and setter methods to access the model.


class Cat < CouchRest::Model::Base
  belongs_to :mother
  property :name

kitty = => "Felix")
kitty.mother = Mother.find_by_name('Sophie')

Providing a object to the setter, mother in the example will automagically update the mother_id attribute. Retrieving the data later is just as expected:

kitty = Cat.find_by_name "Felix" == 'Sophie'

Belongs_to accepts a few options to add a bit more felxibility:

  • :class_name - the camel case string name of the class used to load the model.
  • :foreign_key - the name of the property to use instead of the attribute name with _id on the end.
  • :proxy - a string that when evaluated provides a proxy model that responds to #get.

The last option, :proxy is a feature currently in testing that allows objects to be loaded from a proxy class, such as ClassProxy. For example:

class Invoice < CouchRest::Model::Base
  attr_accessor :company
  belongs_to :project, :proxy => ''

A project instance in this scenario would need to be loaded by calling #get(project_id) on in the scope of an instance of the Invoice. We hope to document and work on this powerful feature in the near future.

Collection Of

A collection_of relationship is much like belongs_to except that rather than just one foreign key, an array of foreign keys can be stored. This is one of the great features of a document database. This relationship uses a proxy object to automatically update two arrays; one containing the objects being used, and a second with the foreign keys used to the find them.

The best example of this in use is with Labels:

class Invoice < CouchRest::Model::Base
  collection_of :labels

invoice =
invoice.labels << Label.get('xyz')
invoice.labels << Label.get('abc'){|l|} # produces ['xyz', 'abc']

See the belongs_to relationship for the options that can be used. Note that this isn't especially efficient, a get is performed for each model in the array. As with a has_many relationship, we hope to be able to take advantage of the Linked Documents feature to avoid multiple requests.


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

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.


# 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') {

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

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

Pretty cool!

Proxy Support

CouchDB makes it really easy to create databases on the fly, so easy in fact that it is perfectly feasable to have one database per user or per company or per whatever makes sense to split into its own individual database. CouchRest Model now makes it really easy to support this scenario using the proxy methods. Here's a quick example:

# Define a master company class, its children should be in their own DB
class Company < CouchRest::Model::Base
  use_database COUCHDB_DATABASE
  property :name
  property :slug

  proxy_for :invoices

  def proxy_database
    @proxy_database ||= COUCHDB_SERVER.database!("project_#{slug}")

# Invoices belong to a company
class Invoice < CouchRest::Model::Base
  property :date
  property :total

  proxied_by :company

  design do
    view :by_date

By setting up our models like this, the invoices should be accessed via a company object:

company = Company.first            # build a new invoice
company.invoices.by_date.first  # find company's first invoice by date

Internally, all requests for invoices are passed through a model proxy. Aside from the basic methods and views, it also ensures that some of the more complex queries are supported such as validating for uniqueness and associations.


CouchRest Model supports a few configuration options. These can be set either for the whole Model code base or for a specific model of your chosing. To configure globally, provide something similar to the following in your projects initializers or environments:

CouchRest::Model::Base.configure do |config|
  config.mass_assign_any_attribute = true
  config.model_type_key = 'couchrest-type'

To set for a specific model:

class Cat < CouchRest::Model::Base mass_assign_any_attribute true end

Options currently avilable are:

  • mass_assign_any_attribute - false by default, when true any attribute may be updated via the update_attributes or attributes= methods.
  • model_type_key - 'model' by default, is the name of property that holds the class name of each CouchRest Model.
  • auto_update_design_doc - true by default, every time a view is requested and this option is true, a quick check will be performed to ensure the model's design document is up to date. When disabled, you're design documents will never be updated automatically and you'll need to perform updates manually. Results are cached on a per-database and per-design basis to help lower the number of requests. See the View section for more details.

Notable Issues

None at the moment...


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).



Check the wiki for documentation and examples


Please post bugs, suggestions and patches to the bug tracker at

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