BeckDesignRules for Database Developers Part 1: Passes the tests

Software design and software architecture are topics which are sometimes associated with distant, slightly mad geniuses, living in an ivory tower and regularly throwing UML diagrams to their ground crew of “normal” developers. They are seen as arcane knowledge which can only be absorbed by the most experienced, most talented “10x developers“, “rockstars” and “ninjas”.

From my experience, this point of view couldn’t be farther from reality. On the contrary I see software design and architecture as fundamental parts of any kind of development work. The moment we start writing code, we will make decisions and are creating software design, no matter if we are aware or not.
Of course there might be guidelines, there might be an architecture given by others, there might even be detailed API descriptions and an abstract design which paints the big picture, but in the end the little, daily decisions will have a huge impact on the result.

Understanding the rules of good software design is therefore a topic which affects developers of any skill and experience level.
Knowledge in that field will be extremely beneficial for every task related to software development.

Four Rules of Simple Design

Kent Beck, developer of Extreme Programming (XP) and Test-Driven Development (TDD), came up with four rules of simple software design in the late 1990s, which Martin Fowler expresses like this:


Martin gives a great, comprehensible description in his article about the “BeckDesignRules” which is also the source of the picture above.

I will try to take a deep dive into these rules, their spirit and how they can be practically done in database development. There is also much personal interpretation from my side and I’m not entirely sure whether Kent Beck would agree on all of my thoughts (of course I hope so).

I will split this up into several blog posts (you wouldn’t believe how hard it is anyway to keep my personal goal of one post per month) and today’s post will cover the first, probably most important and impactful of Beck’s design rules:

Passes the Tests

This one is clearly about Unit-Testing, Test-Driven Development and lots of green lights in your testing report, isn’t it? It means that good software design must adopt specific patterns from XP or other agile methodologies, right?
Continue reading


“One does not simply update a database” – migration based database development


I already described in a previous post why databases are different to applications from a development perspective. The most impactful difference in my opinion is, that you can deploy applications by state. You pick a certain point in your version control system, build your application and have a certain state of your application at hand.

Best case, this state is backed by a number of self-tests and has a unique version number (well, it has one by the hash of your specific commit). You take that build and can deploy it, no matter if your customer had a different version (state) of your application installed or not.

Of course this is simplified, there might be external APIs, libraries, configuration files or – who had thought – databases which prevent you from easily switching application states, but normally such constraints are relatively few.

Databases are different. You can’t preserve state in a database once it’s shipped to a customer. The moment you give it out of your hands, a database starts to change its state continuously. You cannot simply “install” a new version of your database schema on a customer database – there’s data to be preserved and in most cases it’s not even possible to clearly separate schema and data.
And yes, data changes for applications, too, but in my experience database schema is usually much tighter coupled to the data than applications are (which makes sense, doesn’t it?).

So, how do we overcome these difficulties, especially if we are aiming towards frequent releases and agile, collaborative development? Continue reading