Architecture Patterns with Python

Chapter 4. Our First Use Case: Flask API and Service Layer

Back to our allocations project! Figure 4-1 shows the point we reached at the end of Chapter 2, which covered the Repository pattern.

Figure 4-1. Before: we drive our app by talking to repositories and the domain model

In this chapter, we discuss the differences between orchestration logic, business logic, and interfacing code, and we introduce the Service Layer pattern to take care of orchestrating our workflows and defining the use cases of our system.

We’ll also discuss testing: by combining the Service Layer with our repository abstraction over the database, we’re able to write fast tests, not just of our domain model but of the entire workflow for a use case.

Figure 4-2 shows what we’re aiming for: we’re going to add a Flask API that will talk to the service layer, which will serve as the entrypoint to our domain model. Because our service layer depends on the AbstractRepository, we can unit test it by using FakeRepository but run our production code using SqlAlchemyRepository.

Figure 4-2. The service layer will become the main way into our app

In our diagrams, we are using the convention that new components are highlighted with bold text/lines (and yellow/orange color, if you’re reading a digital version).

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