Introduction to the Application Layer
Until now, we've been creating ad hoc functions, testing them out at the REPL, occasionally creating a namespace or two that brings them together. We can think of the application layer as bringing all those namespaces and functions together into a working, coherent application with an associated API. In essence, we are designing the backend of our application in this step. We will then learn how to expose that API via REST in the next chapter; it will be useful to bear that in mind as we design our application.
When designing our application layer, it makes sense to take a step back and ask what our requirements are. If we consider the activity tracking application, we might realistically have the following high-level requirements:
- Create a new user.
- Create an activity for a given user.
- Query users and activities.
- Run reports across individual users (that is, by activity or time period).
Implementing the preceding...
