Decor

Define multiple representations of an object.

Read the documentation or see an example scenario and usage below.

Scenario

You have an API. It returns provides access to a User resource. This resource:

create_table do |t|
  t.string :screen_name
  t.string :state,  :default => "active"
  t.string :role,   :default => "user"
end

class User < ActiveRecord::Base
  STATES  = ["active", "inactive"]
  ROLES   = ["user", "admin"]
end

At one point, you had just defined booleans for active and admin, but you have plans to expand the states and roles of a User. However, you already provide an API that you do not wish to break.

How do you transition your code and your data over and not break backwards compatibility? How do you do this modularly and in an easily testable way without making your API endpoints (controllers et al) heavy?

How about:

class User < ActiveRecord::Base
  include Decor
  
  STATES  = ["active", "inactive"]
  ROLES   = ["user", "admin"]
  
  version "v1" do
    def active
      state == "active"
    end
    def admin
      role == "admin"
    end
    
    def as_json(options = {})
      super(options.merge(:only => [:screen_name],
                          :methods => [:active, :admin]))
    end
  end
  
  version "v2" do
    def as_json(*args)
      super(options.merge(:only => [:screen_name, :state, :role]))
    end
  end
  
end

Then, our endpoint:

get '/api/:version/users/:id' do
  @user = User.find(params[:id])
  @user.for(version).to_json
end

You can also include external resources providing some contextual influence over how your resources choose to represent themselves:

class User < ActiveRecord::Base
  include Decor
  
  version "v3" do
    def screen_name
      "%s (%s)" % [super, organization.name]
    end
  end
  
end

get '/api/:version/organizations/:org_id/users/:id' do
  @organization = Organization.find(params[:org_id])
  @user = User.find(params[:id]).for(version, :organization => @organization)
  @user.to_json
end

Example Usage

Defining your class and versions:

class Resource < Struct.new(:name, :value)
  include Decor
  
  version "v1" do
    # a computed value specific to this version
    def computed
      value * 10
    end
  end
  
  version "v2" do
    # overloaded name
    def name
      super.reverse
    end
    
    # different computed value for this version
    def computed
      value * 100
    end
  end
  
  def unversioned
    "yes"
  end
end

Using the versioned instance:

resource = resource.for(version)

TODOs

• delegate to other versions

Contributing

Feel free to open Issues or fork and create Pull Requests.

The minimum for contribution is a failing spec. If you can at least convey what the problem is or the feature you’d like to add in a failing spec, I will be much more motivated to fix the issue or add the feature.

If you’d like to fix the bug or implement the feature yourself, feel free to! Please document and test your code thoroughly and in similar fashion to what already exists.

Copyright and License

The MIT License

Copyright © 2010 Matt Todd.

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the “Software”), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.