Nowadays developing web applications usually requires a flexible process due to changing business logic, shifting priorities or new insights. Besides choosing the right methodology this also requires designing the application in such a way that this flexibility can be achieved. [...] In this article I will show how to implement a specific case using Doctrine 2. Full code accompanying this article can be found on GitHub.
He starts by describing the entities (User/TimeSheet/TimeSheetStatusChange) and how they're defined in Doctrine objects. He modifies them to build in some business-level restrictions like "status changes are only allowed in a certain order". He shows that the domain models presented are about more than just working with the database tables. They enforce rules that effect the flow of the application as well.