What’s New?

• 2009-05-27
  • Added minimal support for data migrations. Although CouchDB’s nature removes the necessity for migrations, certain knowledge that all objects possess a particular property can simplify client logic. This desire for simplification is the rationale behind this change.
• 2009-04-19
  • Defaults to taf2-curb, falling back to Net/HTTP if it taf2-curb can’t be loaded. Thanks to Fred Cheung.
  • For those interested in using RelaxDB with an ETag based cache, look here

• 2009-03-31
  • RelaxDB 0.3 released – compatible with CouchDB 0.9.

Overview

RelaxDB provides a Ruby interface to CouchDB. It offers a simple idiom for specifying object relationships. The underlying objects are persisted to CouchDB and are retreived using CouchDB idioms.

A few facilities are provided including pretty printing of GET requests and uploading of JavaScript views.

A basic merb plugin, merb_relaxdb is also available.

For more complete documentation take a look at docs/spec_results.html and the corresponding specs.

Note: While RelaxDB 0.3 is explicitly compatible with CouchDB 0.9, HEAD typically tracks CouchDB HEAD.

Details

Getting started

  require 'rubygems'
  require 'relaxdb'

  RelaxDB.configure :host => "localhost", :port => 5984, :design_doc => "app"
  RelaxDB.use_db "relaxdb_scratch"
  
  RelaxDB.enable_view_creation # creates views when class definition is executed

Defining models

class User < RelaxDB::Document
  property :name
end

class Invite < RelaxDB::Document
  
  property :created_at
  
  property :event_name
  
  property :state, :default => "awaiting_response",
    :validator => lambda { |s| %w(accepted rejected awaiting_response).include? s }
  
  references :sender, :validator => :required
  
  references :recipient, :validator => :required
  
  property :sender_name,
   :derived => [:sender, lambda { |p, o| o.sender.name } ]
  
  view_by :sender_name
  view_by :sender_id
  view_by :recipient_id, :created_at, :descending => true
  
  def on_update_conflict
    puts "conflict!"
  end
  
end

Exploring models

# Saving objects

sofa = User.new(:name => "sofa").save!
futon = User.new(:name => "futon").save!

i = Invite.new :sender => sofa, :recipient => futon, :event_name => "CouchCamp"
i.save!

# Loading and querying

il = RelaxDB.load i._id
puts i == il # true

ir = Invite.by_sender_name "sofa"
puts i == ir # true

ix = Invite.by_sender_name(:key => "sofa").first
puts i == ix # true

# Denormalization

puts ix.sender_name # prints sofa, no requests to CouchDB made
puts ix.sender.name # prints sofa, a single CouchDB request made

# Saving with conflicts

idup = i.dup
i.save!
idup.save     # conflict printed

# Saving with and without validations

i = Invite.new :sender => sofa, :event_name => "CouchCamp"

i.save! rescue :ok      # save! throws an exception on validation failure or conflict
i.save                  # returns false rather than throwing an exception
puts i.errors.inspect   # prints {:recipient=>"invalid:"}

i.validation_skip_list << :recipient  # Any and all validations may be skipped
i.save                                # succeeds

Paginating models

  # Controller

  def show(page_params={})
    uid = @user._id
    @invites = Invite.paginate_by_sender_name :startkey => [uid, {}], 
        :endkey => [uid], :descending => true, :limit => 5, :page_params => page_params
    render
  end
  
  # In your view
  
  <% @invites.each do |i| %>
    <%= i.event_name %>
  <% end %>
  
  <%= link_to "prev", "/invites/?#{@invites.prev_query}" if @invites.prev_query %>
  <%= link_to "next", "/invites/?#{@invites.next_query}" if @invites.next_query %>  

More illustrative examples are listed in the .paginate_view spec in spec/paginate_spec.rb

Creating views by hand

  $ cat view.js 
  function Invites_by_state-map(doc) {
    if(doc.relaxdb_class === "Invite")
      emit(doc.state, doc);
  }

  function Invites_by_state-reduce(keys, values, rereduce) {
    if (rereduce) {
      return sum(values);
    } else {
      return values.length;
    }
  }
  $

  RelaxDB::ViewUploader.upload("view.js")
  RelaxDB.view "Invites_by_state", :key => "accepted", :reduce => true

Migrations

  $ cat 001_double.rb
  RelaxDB::Migration.run Primitives do |p| 
    p.num *= 2 
    p
  end
  
  $ ruby -e 'RelaxDB::Migration.run_all Dir["./*.rb"]'

Visualise

Fuschia offers a web front end for visualising inter-document relationships.

Incomplete list of limitations

• Destroying an object results in non transactional nullification of child/peer references
• Objects can talk to only one database at a time. Similarly for design docs.