Event sourcing example
Usage
Note: This project depends on a personal GitHub Package Registry. In order to build locally, it is necessary to set USERNAME and TOKEN environment variables. Instructions for the generation of a token are available in Creating a personal access token.
Run tests: mvn clean test
Run mutation coverage: mvn org.pitest:pitest-maven:mutationCoverage
Use case
A business has to manage interventions.
For each intervention, it is possible to create some reminders.
- A reminder is scheduled at a given time.
- A reminder can be assigned to a country and to a person.
- A reminder has a status in a lifecycle.
Event sourcing
Event Sourcing is an architectural approach, which consists of keeping track not of the current state, but of the entire sequence of state transitions (Events) which led to it. Events are the "source of truth" of the system, from which the current state (or any past state) is inferred.
The aggregate contains 2 types of functions:
- The decide function basically consists in deciding which events need to be created following a command. This is where all the business logic of the aggregate is located.
- Input: command + former state
- Output: event(s)
- The apply function consists in updating the state of the aggregate from an event.
- Input: event + former state
- Output: updated state