Couch Potato

... is a persistence layer written in ruby for CouchDB.

Mission

The goal of Couch Potato is to create a minimal framework in order to store and retrieve Ruby objects to/from CouchDB and create and query views.

It follows the document/view/querying semantics established by CouchDB and won't try to mimic ActiveRecord behavior in any way as that IS BAD.

Code that uses Couch Potato should be easy to test.

Lastly Couch Potato aims to provide a seamless integration with Ruby on Rails, e.g. routing, form helpers etc.

Core Features

• persisting objects by including the CouchPotato::Persistence module
• declarative views with either custom or generated map/reduce functions
• extensive spec suite

Installation

Couch Potato is hosted as a gem on gemcutter.org which you can install like this:

sudo gem install couch_potato --source http://gemcutter.org

Using with your ruby application:

require 'rubygems'
require 'couch_potato'

Alternatively you can download or clone the source repository and then require lib/couch_potato.rb.

You MUST specify the name of the database:

CouchPotato::Config.database_name = 'name_of_the_db'

The server URL will default to http://localhost:5984/ unless specified:

CouchPotato::Config.database_name = "http://example.com:5984/name_of_the_db"

Using with Rails

Add to your config/environment.rb:

config.gem 'couch_potato', :source => 'http://gemcutter.org'
config.frameworks -= [:active_record] # if you switch completely

Then create a config/couchdb.yml:

development: development_db_name
test: test_db_name
production: http://db.server/production_db_name

Alternatively you can also install Couch Potato directly as a plugin.

Introduction

This is a basic tutorial on how to use Couch Potato. If you want to know all the details feel free to read the specs and the rdocs.

Save, load objects

First you need a class.

class User
end

To make instances of this class persistent include the persistence module:

class User
  include CouchPotato::Persistence
end

If you want to store any properties you have to declare them:

class User
  include CouchPotato::Persistence

  property :name
end

Properties can be typed:

class User
  include CouchPotato::Persistence

  property :address, :type => Address
end

In this case Address also implements CouchPotato::Persistence which means its JSON representation will be added to the user document.
Couch Potato also has support for the basic types (right now only Fixnum is supported):

class User
  include CouchPotato::Persistence

  property :age, :type => Fixnum
end

With this in place when you set the user's age as a String (e.g. using an hTML form) it will be converted into a Fixnum automatically.

Properties can have a default value:

class User
  include CouchPotato::Persistence

  property :active, :default => true
end

Now you can save your objects. All database operations are encapsulated in the CouchPotato::Database class. This separates your domain logic from the database access logic which makes it easier to write tests and also keeps you models smaller and cleaner.

user = User.new :name => 'joe'
CouchPotato.database.save_document user # or save_document!

You can of course also retrieve your instance:

CouchPotato.database.load_document "id_of_the_user_document" # => <#User 0x3075>

Properties

You can access the properties you declared above through normal attribute accessors.

user.name # => 'joe'
user.name = {:first => ['joe', 'joey'], :last => 'doe', :middle => 'J'} # you can set any ruby object that responds_to :to_json (includes all core objects)
user._id # => "02097f33a0046123f1ebc0ebb6937269"
user._rev # => "2769180384"
user.created_at # => Fri Oct 24 19:05:54 +0200 2008
user.updated_at # => Fri Oct 24 19:05:54 +0200 2008
user.new? # => false

If you want to have properties that don't map to any JSON type, i.e. other than String, Number, Boolean, Hash or Array you have to define the type like this:

class User
  property :date_of_birth, :type => Date
end

The date_of_birth property is now automatically serialized to JSON and back when storing/retrieving objects.

Dirty tracking

CouchPotato tracks the dirty state of attributes in the same way ActiveRecord does:

user = User.create :name => 'joe'
user.name # => 'joe'
user.name_changed? # => false
user.name_was # => nil

You can also force a dirty state:

user.name = 'jane'
user.name_changed? # => true
user.name_not_changed
user.name_changed? # => false
CouchPotato.database.save_document user # does nothing as no attributes are dirty

Object validations

Couch Potato uses the validatable library for validation (http://validatable.rubyforge.org/)\

class User
  property :name
  validates_presence_of :name
end

user = User.new
user.valid? # => false
user.errors.on(:name) # => [:name, 'can't be blank']

Finding stuff

In order to find data in your CouchDB you have to create a view first. Couch Potato offers you to create and manage those views for you. All you have to do is declare them in your classes:

class User
  include CouchPotato::Persistence
  property :name

  view :all, :key => :created_at
end

This will create a view called "all" in the "user" design document with a map function that emits "created_at" for every user document.

CouchPotato.database.view User.all

This will load all user documents in your database sorted by created_at.

CouchPotato.database.view User.all(:key => (Time.now- 10)..(Time.now), :descending => true)

Any options you pass in will be passed onto CouchDB.

Composite keys are also possible:

class User
  property :name

  view :all, :key => [:created_at, :name]
end

You can also pass conditions as a JavaScript string:

class User
  property :name

  view :completed, :key => :name, :conditions => 'doc.completed = true'
end

The creation of views is based on view specification classes (see CouchPotato::View::BaseViewSpec and its descendants for more detailed documentation). The above code uses the ModelViewSpec class which is used to find models by their properties. For more sophisticated searches you can use other view specifications (either use the built-in or provide your own) by passing a type parameter:

If you have larger structures and you only want to load some attributes you can use the PropertiesViewSpec (the full class name is automatically derived):

class User
  property :name
  property :bio

  view :all, :key => :created_at, :properties => [:name], :type => :properties
end

CouchPotato.database.view(User.everyone).first.name # => "joe" CouchPotato.database.view(User.everyone).first.bio # => nil

You can also pass in custom map/reduce functions with the custom view spec:

class User
  view :all, :map => "function(doc) { emit(doc.created_at, null)}", :include_docs => true, :type => :custom
end

If you don't want the results to be converted into models the raw view is your friend:

class User
  view :all, :map => "function(doc) { emit(doc.created_at, doc.name)}", :type => :raw
end

When querying this view you will get the raw data returned by CouchDB which looks something like this: 2, 'rows': [{'value': 'alex', 'key': '2009-01-03 00:02:34 +000', 'id': '75976rgi7546gi02a']}

To process this raw data you can also pass in a results filter:

class User
  view :all, :map => "function(doc) { emit(doc.created_at, doc.name)}", :type => :raw, :results_filter => lambda {|results| results['rows'].map{|row| row['value']}}
end

In this case querying the view would only return the emitted value for each row.

You can pass in your own view specifications by passing in :type => MyViewSpecClass. Take a look at the CouchPotato::View::*ViewSpec classes to get an idea of how this works.

Associations

Not supported. Not sure if they ever will be. You can implement those yourself using views and custom methods on your models.

Callbacks

Couch Potato supports the usual lifecycle callbacks known from ActiveRecord:

class User
  include CouchPotato::Persistence

  before_create :do_something_before_create
  before_update {|user| user.do_something_on_update}
end

This will call the method do_something_before_create before creating an object and run the given lambda before updating one. Lambda callbacks get passed the model as their first argument. Method callbacks don't receive any arguments.

Supported callbacks are: :before_validation, :before_validation_on_create, :before_validation_on_update, :before_validation_on_save, :before_create, :after_create, :before_update, :after_update, :before_save, :after_save, :before_destroy, :after_destroy.

If you need access to the database in a callback: Couch Potato automatically assigns a database instance to the model before saving and when loading. It is available as database accessor from within your model instance.

Attachments

There is basic attachment support: if you want to store any attachments set that _attachments attribute of a model before saving like this:

class User
  include CouchPotato::Persistence
end

user = User.new
user._attachments = {'photo' => {'data' => '[image byte data]', 'content_type' => 'image/png'}}

When saving this object an attachment with the name photo will be uploaded into CouchDB. It will be available under the url of the user object + /photo. When loading the user at a later time you still have access to the content_type and additionally to the length of the attachment:

user_reloaded = CouchPotato.database.load user.id
user_reloaded._attachments['photo'] # => {'content_type' => 'image/png', 'length' => 37861}

Testing

To make testing easier and faster database logic has been put into its own class, which you can replace and stub out in whatever way you want:

class User
  include CouchPotato::Persistence
end

# RSpec
describe 'save a user' do
  it 'should save' do
    couchrest_db = stub 'couchrest_db',
    database = CouchPotato::Database.new couchrest_db
    user = User.new
    couchrest_db.should_receive(:save_doc).with(...)
    database.save_document user
  end
end

By creating you own instances of CouchPotato::Database and passing them a fake CouchRest database instance you can completely disconnect your unit tests/spec from the database.

Testing map/reduce functions

Couch Potato provides custom RSpec matchers for testing the map and reduce functions of your views. For example you can do this:

Class User
  include CouchPotato::Persistence

  view :by_name, :key => :name
  view :by_age, :key => :age
end

#RSpec
require 'couch_potato/rspec/matchers'

describe User, 'by_name' do
  it "should map users to their name" do
    User.by_name.should map({:name => 'bill', :age => 23}).to(['bill', null])
  end

  it "should reduce the users to the sum of their age" do
    User.by_age.should reduce([], [[23], [22]]).to(45)
  end

  it "should rereduce" do
    User.by_age.should rereduce([], [[23], [22]]).to(45)
  end
end

This will actually run your map/reduce functions in a JavaScript interpreter, passing the arguments as JSON and converting the results back to Ruby. For more examples see the spec.

In order for this to work you must have the js executable in your PATH. This is usually part of the spidermonkey package/port. (On MacPorts that's spidemonkey, on Linux it could be one of libjs, libmozjs or libspidermonkey). When you installed CouchDB via your packet manager Spidermonkey should already be there.

Helping out

Please fix bugs, add more specs, implement new features by forking the github repo at http://github.com/langalex/couch_potato.

You can run all the specs by calling 'rake spec_unit' and 'rake spec_functional' in the root folder of Couch Potato. The specs require a running CouchDB instance at http://localhost:5984

I will only accept patches that are covered by specs - sorry.

Contact

If you have any questions/suggestions etc. please contact me at alex at upstream-berlin.com or @langalex on twitter.