In fact, it's feasible to wrap collections of domain objects inside a fairly flexible business transactional model and just perform several database writes/deletes in one go, therefore avoiding having to break down the process into more atomic and expensive database calls, which always lead to the session-per-operation antipattern. Moreover, this transaction-based mechanism rests on the academic formalities of a design pattern commonly known as Unit of Work (UOW), and its implementation in several popular enterprise-level packages, such as Hibernate, is quite prolific and prosperous.
He shows how to implement the "Unit of Work" design pattern via a "UnitOfWorkInterface" and a "UnitOfWork" class that implements it. The class provides methods for things like entity handling (CRUD operations) and working with the data mapper for the transactions. He also includes the code to implement the data mapper, a layer on top of a PDO-based interface that also provides CRUD operations for the data records. From this, he defines a domain model, "User", and shows how to create a new user, register it with the UnitOfWork instance and do things like update a property, delete the record and pull out the user's information.