Mathias Noback has posted another in his series looking at the concepts and implementation of command bus handling in PHP. In this new post he looks at some of the responsibilities of the bus and provides a few examples to help drive the point home.
In the previous post we looked at commands and how you can use them to separate technical aspects of the input, from the actual behavior of your application. Commands are simple objects, handed over to the command bus, which performs the change that is needed. [...] So the command bus contains some kind of a lookup mechanism to match commands with their handlers. Some command bus libraries use a naming convention here (e.g. handler name = command name + "Handler"), some use a kind of service locator, etc.
He starts off talking about the main point of the article, giving an overview of what he sees are the basic responsibilities of the command bus. He also sheds some light on methods he's seen for keeping it from becoming a "big inarticulate unmaintainable class". He then gets into his two examples: database transaction handling and protecting the original order of commands. He shows how his SimpleBus package handles most of this for you and shows how it follows the "chain of responsibility" design pattern to make it work.