Why external systems are difficult
In this section, we’re going to review the driving force behind the hexagonal architecture approach – the difficulty of working with external systems. Dependencies on external systems cause problems in development. The solution leads to a nice design approach.
Let’s look at a simple way of handling external systems. The task of our user is to pull a report of this month’s sales from a database. We will write one piece of code that does exactly that. The software design looks like this:
Figure 9.1 – One piece of code does everything
In this design, we have sales data stored in a database in the usual way. We write some code to pull the report on behalf of our user. It is a single piece of code that does the whole job as a single step. It will connect to the database, send a query, receive the results, do some processing, and format the results ready for the user to read.
On the...
