Domain-Driven Design in PHP

Small Aggregates Vs. Big Aggregates

For most of the websites and projects where we've worked, almost 95 percent of Aggregates were formed by one single root Entity and some Value Objects. No other Entities were required to be in the same Aggregate. So in most cases, there was no real true business invariant to keep consistent.

Be careful with the has-a/has-many relations that don't necessarily make two Entities become one Aggregate, with one of those being the root. Relations, as we will see, can be handled by referencing Entity Identities.

As explained in the introduction, an Aggregate is a transactional boundary. The smaller the boundary is, the fewer chances there are for conflicts when committing multiple concurrent transactions. When ...