DDD in PHP Experiment

Domain-Driven Design in PHP Experiment and Project Seed

A current and difficult software development project has recently sent me scurrying for answers. In that search I’ve rediscovered the book Domain-Driven Design: Tackling Complexity in the Heart of Software by Eric Evans. In addition to re-reading the book and reviewing a handful of slide-decks at SlideShare; I have found that there a few different and even wide varying implementations of the principles of domain-driven design. So I have started a Github project to test out the implementation differences.

  • First, I am looking at the differences in the persistence and database access (DBAL) components in the infrastructure layer.

    • For example one question that needs to be answered is should a DataMapper reside in the Domain or Infrastructure layer.
    • Another is should the DataMapper be implemented following the pattern religiously or with application specific variations.
    • Is it really a DataMapper or is it better called a DomainMapper that then uses TableDataGateways and RowDataGateways to read from persistence storage?
    • Is there a DataMapper class in the infrastructure layer that communicates with the DomainMapper in the domain layer? That these two objects can pull from multiple tables using SQL and create a single entity or a single aggregate entity.

  • Second, I am looking at the differences in how domain classes versus infrastructure classes are constructed via factories.

    • Which factory pattern is a best practice?
    • If the factory method pattern is the best practice should it be implemented religiously or with variations?

  • Thirdly, where can I use things like memcached or an op-code cache to improve the performance of large data sets.

    • Data sets such as a repository might easily grow beyond a thousand aggregate root entities with maybe over tens times that in regular entities.
    • Large data sets could easily cause the database syndrome known as ‘death by a thousand cuts’ meaning that a repository during a load process could easily ask the infrastructure layer to make a lot of database calls bringing the server to it’s knees.

Anyways, it should turn into a great learning experience.