Contents

Setting up for DI is very similar to the setup for a service locator, but instead of passing the locator (we'll call it a _registry_ now), we only pass (or set) the dependencies that the service itself needs.

<pre>
  require 'needle'

  def create_application
    registry = Needle::Registry.define do |b|
      b.view          { View.new }
      b.logger        { Logger.new }
      b.database      { Database.new( b.logger ) }
      b.authenticator { Authenticator.new(b.logger, b.database) }
      b.session       { Session.new(b.logger, b.database) }

      b.app do
        app = Application.new
        app.logger = b.logger
        app.view = b.view
        app.database = b.database
        app.authenticator = b.authenticator
        app.session = b.session
        app
      end
    end

    registry[:app]
  end

  class Application
    attr_writer :view, :logger, :database, :authenticator, :session
  end

  class Session
    def initialize( logger, database )
      @database = database
      @logger = logger
    end
  end

  ...
</pre>

The @create_application@ method is now (necessarily) a little more complex, since it now contains all of the initialization logic for each service in the application. However, look how much simpler this made the other classes, especially the @Application@ class.

Now, each class no longer even needs to care that it is being initialized via another container. All it knows is that when it is created, it will be given each of its dependencies (either as constructor parameters or as property accessors).

Version data entries

4 entries across 4 versions & 1 rubygems

Version	Path
needle-1.0.0	doc/manual/parts/04_setup.txt
needle-1.1.0	doc/manual/parts/04_setup.txt
needle-0.9.0	doc/manual/parts/04_setup.txt
needle-1.2.0	doc/manual/parts/04_setup.txt