SalesEngine Demo

This very-light skeleton demonstrates on way to connect a merchant to their items. Things to notice:

• repository_integration_test.rb has the one test. Run it with ruby test/repository_integration_test.rb
• It creates an instance of SalesEngine. Look at the sales_engine.rb to see that the new SalesEngine initializes both a MerchantRepository and a ItemRepository, but most importantly that it passes those objects self which is a reference to the SalesEngine instance.
• The initializers of both MerchantRepository and ItemRepository store that reference as engine so they can later reach back up to the SalesEngine they came from
• When MerchantRepository creates Merchant instances (line 9 in the merchants method), it again passes self in as a parameter. That self is the MerchantRepository instance.
• The test calls the .items method on a Merchant instance. In merchant.rb see how the items method reaches up to the repository (the parent instance of MerchantRepository) and asks for the items_for and passes itself up to the repo.
• In MerchantRepository#items_for, the repo reaches up to the engine and calls the items_for_merchant_id and passes in the ID number of the merchant parameter
• In SalesEngine, the items_for_merchant_id method just calls find_all_by_merchant_id on the item_repository instance it instantiated in the initialize
• ItemRepository#find_all_by_merchant_id actually does the select, and passes the results back to the SalesEngine, which passes them back to the MerchantRepository, which passes them back to the Merchant instance, which passes them back to the test.
• The test assertion succeeds, having found three items.

No problem, right? :)