Implementing Domain-Driven Design

Avoid Dependency Injection

Dependency injection of a Repository or Domain Service into an Aggregate should generally be viewed as harmful. The motivation may be to look up a dependent object instance from inside the Aggregate. The dependent object could be another Aggregate, or a number of them. As stated earlier under “Rule: Reference Other Aggregates by Identity,” preferably dependent objects are looked up before an Aggregate command method is invoked, and passed in to it. The use of Disconnected Domain Model is generally a less favorable approach.

Additionally, in a very high-traffic, high-volume, high-performance domain, with heavily taxed memory and garbage collection cycles, think of the potential overhead of injecting Repositories and ...