Comment by zapov | Hacker News Reader

Comment by zapov | Hacker News Reader

While I like DDD very much (created much tooling over last 10 years to help develop software in such a way), but if you move outside of useful implementations, you don't end up with much. Talking to domain experts, analyzing your domain... that's just a straw man arguments to sell DDD. Ubiquitous language is a good argument for DDD, but I don't see that practised a lot. There is often a noticeable disconnect between how experts talk about the system and the abstractions in the system which represent them.

Also, on technical level, while there are a lot of useful things in DDD (aggregate roots, value objects, repositories, ...) there is also a cargo-cult like notion what is a good way to develop software. And when you listen to "the experts" you often get a feeling they can fake the talk, but surely don't know how to walk.

My single question to see if someone is practicing DDD is: do you refactor your codebase on deeper insights? I'm yet to see someone say yes to that. Often you get excuses not to touch code which is working since refactoring large codebase is impractical/risky.

I refactor my code fairly regularly (as specifications change). The use of TDD, DDD, CQRS and Event Sourcing gives me immense flexibility to be able to refactor a large codebase and then test it through its whole lifespan (with actual data).

> The use of TDD, DDD, CQRS and Event Sourcing gives me immense flexibility to be able to refactor a large codebase and then test it through its whole lifespan (with actual data).

What is your experience in applying those principles in a team? It would be very interesting to get some insight on it.

1. TDD is simple enough. Everyone should be doing it. 2. DDD - this usually results in plenty of healthy debates on naming conventions. Acronyms are abhorred and we try to agree with the stakeholders on the meaning of each word they use. 3. CQRS and Event Sourcing - this has required our team quite a bit more of startup time than a CRUD application would have. We have been lucky to have a very understanding Product Owner who gives us plenty of time to deal with tech debt. Although single features may have originally taken us longer (than the time it would have taken to do the same with CRUD) at the start of the project, years on this time and the complexity of refactoring or adding features has not really increased, as any functionality is contained within its bounded context.

The biggest difficulty has been explaining what we are doing and why to senior management. But we haven't had any bad incidents so far, so I think they like us.

Do you do full-blown event sourcing or apply it to specific areas only? If the latter, how do you decide which? How do you deal with performance? Specialized database (e.g. Event Store) or not?

Real life success stories about ES are rare, so I'd love to get more insight in the anatomy of the solution (way beyond these few questions). Blog post request, I guess.

We have full-blown event sourcing for pretty much everything. The performance on the read side is great (obviously). We have an Event Store and we rebuild the Domain for every new command, so it isn't particularly fast, but we have a situation where commands are only issued a few times every year by a single person, whereas there are millions of reads every day (hence justifying CQRS as a solution). We have a mixed solution around replaying events though, largely around the issues we have with file uploads. Every file upload triggers multiple events (uploaded, processed etc) and we have different solutions for different files. Small files we store in the events as a blob, whereas big file events upload the data to a projection store and will not be replayed, so we don't have the issue of having to keep the original files forever as well as the database. I should probably write a blog post about the project at some point, but I'd like to investigate with my bosses as to how much I can actually reveal about the domain (because it would make the read so much more interesting if I could say everything).

> My single question to see if someone is practicing DDD is: do you refactor your codebase on deeper insights?

I've been wanting to do this for a long time, I've devoted a lot of thought to working out when and how to perform these refactorings. But the reality is, business concerns drive the development of software, not the other way around.

The big reason why refactoring is needed is technical debt, not because the vision of the project changes. You have to get the code clean and well-designed before you'll be able to easily have insights about it. It's all a team can do to chip away at the debt slowly over time barring a bunch of resources devoted to a big cleanup.

In order to make insight-driven refactoring work, you first need to finish cleaning up your debt. Otherwise whenever you try to get started, the debt will get in your way and you'll start yak-shaving until another feature request or bug pops up.

Debt cleanup never gets finished, so refactoring on the basis of insight never gets done either.

Well thats kind of to the point. DDD is all about investing into your core domain since that gives you a business advantage.

In reality domain experts are not available (if existant at all). You implement features in shortest path possible and most of the time never really refactor. Gap between domain and implementation widens... and if you are lucky at one point decide on rewrite which only works if your devs became domain experts themselves.

My solution to that problem is to write software with tools which make refactoring cheap and it's kind of working for me.

> My solution to that problem is to write software with tools which make refactoring cheap and it's kind of working for me.

That. This is how much of a silver bullet as we have had since Brooks wrote his book... Except that it is older, was just kind of forgotten by that time.

> My solution to that problem is to write software with tools which make refactoring cheap and it's kind of working for me.

Relevant link posted a couple of days ago, to optimize for deletion rather than refactoring: https://vimeo.com/108441214.

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