9. Use 2 layered architectural style for reads

Date: 2019-07-01

Log date: 2019-11-04

Status

Accepted

Context

We applied the CQRS style (see ADR 7. Use CQRS architectural style), now we need to decide how to handle reading (querying) requests.

Decision

We will use 2 layered architecture to handle queries: API layer and Application Service layer. As we applied the CQRS and created a separated read model, querying should be straightforward so 2 layers are enough. The API layer is responsible for Query creation based on HTTP request and the module Application layer is responsible for query handling.

Consequences

• Whole query handling logic is in Application Service layer
• Application Service layer is coupled to the database and querying framework
• Solution is simple, easy to understand
• We don't abstract over database
• Performance is better (no object mapping between layers, querying database almost immediately)