Experiment 3: Aggregate with extracted state

This post is third experiment described in post “Experiment: 10 Different implementations of Aggregate“. Experiment 3 is passing sourced IssueState into Issue (AggregateRoot). Business logic is handled by Issue and Issue is emitting domain events. Reflections on this experiment This one seems to be overcomplicated for me. I guess the benefits are in processing events … Read more

Experiment 2: Aggregate with exposed queries

This post is second experiment described in post “Experiment: 10 Different implementations of Aggregate“. This implementation assumed that aggregate is created from a projection of events. Aggregate is not aware of events or anything about event-sourcing. The responsibility of aggregate is to manipulate internal state and business logic. The interesting part for me is about … Read more

Experiment 1: Classical example with AggregateRoot

This post is first experiment described in post “Experiment: 10 Different implementations of Aggregate“. This is a classical and most used example of event-sourcing implementation (Greg Young’s CQRS example). It’s dependent on the framework cause of inheritance from the AggregatRoot base class. I like that it don’t have read methods, so all observability is based … Read more

Experiment: 10 Different implementations of Aggregate

Arkency is a company that shares its experiments with many approaches to DDD aggregate implementation. Some time ago I’ve shared my view on this here. Arkency examples are in Ruby and use an event-sourcing approach. It’s quite different from mine, so some future blog posts will be about reimplementing the Arkency examples in Python. Experiment … Read more

4 ways of mapping Value Object in SQLAlchemy

In the previous post Persistency of DDD aggregate, I described persisting as aggregate with proper application boundaries. Now let’s describe how to persist ValueObject in a relational database using SQLAlchemy and still with boundaries in mind. The persistency of ValueObject in relational databases can be tricky. Unlike entities, there is no id for value objects. We can … Read more

How to add new mutation for cosmic-ray framework

Mutation testing is a concept that I heard some time ago but lately on anti-if course (I highly recommend!) done by Andrzej Krzywda I had a chance to use it in practice. I notice a big difference in the number of mutations generated by different frameworks (mutmut, cosmic-ray, and mutpy) when I was refactoring Gilded … Read more

Tox configuration and integration

Basic tox config Let’s start with a basic config that will run unittest and measure coverage. Important option here is usedevelop = true. With this it won’t install your package to virtualnenv and coverage can be measured. Another thing is to erase previous coverage reports. Codestyle Next, I wanted to check the codestyle. I use pycodestyle, … Read more

Refactoring to BDD-like tests

Sometimes I found myself in a situation where it’s hard to understand what some components suppose to achieve. In these situations, I go to test where scenarios/contracts of this component should be.But then I find some integrations tests with some entries in DB and expected mechanical results.My strategy in this situation is to refactor test … Read more

Process manager VS DDD Aggregate

DDD Aggregate is responsible for encapsulating business logic for the component. But we need to be aware that when we are implementing business logic for a long time process that is coordinating many components, like subscription trial, we have another building block for this. It’s a process manager. Below I pointed out some differences between … Read more