Responsibilities of a persistence adapter

Let’s have a look at what a persistence adapter usually does:

1. Takes the input.
2. Maps the input into database format.
3. Sends the input to the database.
4. Maps the database output into application format.
5. Returns the output.

The persistence adapter takes input through a port interface. The input model may be a domain entity or an object dedicated to a specific database operation, as specified by the interface.

It then maps the input model to a format it can work with to modify or query the database. In Java projects, we commonly use the Java Persistence API (JPA) to talk to a database, so we might map the input into JPA entity objects that reflect the structure of the database tables. Depending on the context, mapping the input model into JPA entities may be a lot of work for little gain, so we’ll talk about strategies without mapping in Chapter 9, Mapping between Boundaries.

Instead of using JPA...