emanuele delbono

Emanuele DelBono

ruby loves DDD (part 3)

In the last post we saw how the controller issue a command to the pipeline, now we will see how this command in managed.

The CommandExecutor finds the handler for the given commmand. In our case the command was AddToBasketCommand and the relative handler is AddToBasketHandler. The code is here:

class AddToBasketHandler
  def execute(add_to_basket_command)
    basket = @repository.get_basket(add_to_basket_command.basket_id)
    basket.add_item (add_to_basket_command.article_id) 
  # more code here...

The aim of a handler is to find the interested aggregate and send messages to it so that it can execute the needed tasks. In our case, we get from the repository an instance of Basket class using the id attribute of the command and we call add_item on that so that our operation will be done. This calls should be made in transaction, but for the sake of simplicity I don’t manage them now. The last call is a message sent to commit method on the aggreate root. This is necessary to confirm the operation, we are saying: ok, we have done with our job. Internally the commit simply apply all the events that were generated in previous methods.