Implementing Domain-Driven Design

Command-Query Responsibility Segregation, or CQRS

It can be difficult to query from Repositories all the data users need to view. This is especially so when user experience design creates views of data that cuts across a number of Aggregate types and instances. The more sophisticated your domain, the more this situation tends to occur.

Using only Repositories to solve this can be less than desirable. We could require clients to use multiple Repositories to get all the necessary Aggregate instances, then assemble just what’s needed into a Data Transfer Object (DTO) [Fowler, P of EAA]. Or we could design specialized finders on various Repositories to gather the disjointed data using a single query. If these solutions seem unsuitable, perhaps we ...