Writing the domain code

In this section, we will look at some of the things we need to think about as we write the code for our domain model. We’ll cover what kinds of libraries we should and should not use in the domain model, how we deal with application configuration and initialization, and we’ll also think about what impact popular frameworks have.

Deciding what should be in our domain model

Our domain model is the very core of our application and the hexagonal architecture puts it up front and center. A good domain model is written using the language of our users’ problem domain; that’s where the name comes from. We should see the names of program elements that our users would recognize. We should recognize the problem being solved over and above the mechanisms we are using to solve it. Ideally, we will see terms from our user stories being used in our domain model.

Applying the hexagonal architecture, we choose our domain model to be independent...