Auditability, diagnostics, time travelling are usually the first mentioned features when speaking about Event Sourcing. All of them are great, but to me, projections are the real killer feature of an event-driven approach. Why? By Oskar Dudycz.
Projections are different interpretations of the same fact. Look at the photo below. Muhammad Ali is standing in triumph over Sonny Liston. Each of them interprets the same fact from an entirely different perspective.
Projections have multiple advantages for the development process. The one that I’d like to highlight especially is reducing the cognitive load. You can break down a process into two parts. At first, on modelling the business logic and capturing its result. Then thinking about how to interpret it. This is a liberating experience from thinking all at once in the relational approach. “Gosh, when I add that field, then this will break foreign key. How do I do this migration?”. Of course, we’ll eventually need to think about connecting our event with the read model, but we can split that thought process.
Projections are powerful but also non-trivial. In theory, it’s just a left-fold approach: you take the current state and apply event data, getting a new one. Yet, things can get more complex if we want a robust, fault-tolerant solution. To learn more and get access to code on TypeScript please follow the link to the full article. Good read!
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