Even when I’m panicking I’m a fan of datamapper.  I like how clean it generally makes my code, but I do notice that I tend to have the same queries cropping up from time to time either in the same application or in other apps using my model library.  This just wasn’t dry enough for me, so I made dm-is-viewable.  It gives sql-like view functionality to DataMapper Resources.  It’s a pretty simple plugin, but lets take a look, um kay?

Let’s start with a really simple User class…

class User
  include DataMapper::Resource
  belongs_to :location

  property :id, Serial
  property :name, String
  property :username, String
  property :password, String

  property :gender, String
  property :age, Integer

  property :favorite_color, String
  property :favorite_number, Integer
end

class Location
  include DataMapper::Resource

  has n, :users

  property :id, Serial
  property :name, String
  property :desc, String
end

Making your resource viewable is pretty easy, first grab the dm-is-viewable gem, then say that your resource is viewable. Views take the exact same parameters that you could pass to Resource.all. The only difference is that dm-is-viewable stores them until they are called.

class User
  include DataMapper::Resource
  is :viewable  

  #lets create some views
  create_view :legal_women, :gender => 'female', :age.gt => 18
  create_view :serial_killers, :favorite_number => 666, :favorite_color => 'black'

  #... Resource code *SNIP SNIP*
end

See the befores and afters below:

# Legal Women Before
User.all(:gender => 'female', :age.gt => 18)

# Legal Women After
User.view :legal_women

# Serial killers before
User.all(:favorite_number => 666, :favorite_color => 'black')

# Serial killers after
User.view :serial_killers

# You can also pass further limiting query parameters to #view.
# Legal Local Women Before
User.all(:gender => 'female', :age.gt => 18, User.location.name => 'Los Angeles')

# Legel Local Women After
User.view :legal_women, User.location.name => 'Los Angeles'

# Passing additional parameters FURTHERS the limitation of records, so..
User.view :legal_women, :gender => 'male'
# => Would return nil, the query would essentially be generated as:
#  SELECT * from users where gender = 'male' and gender = 'female'

Simply, clean, useful. Woot.

Tags: datamapper, dm-is-viewable, ruby

This entry was posted on Friday, December 5th, 2008 at 1:53 pm and is filed under Feature Updates. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.