Events schema versioning, or in other words, events evolution, is one of the first questions I get when explaining Event Sourcing. The topic may look scary, as how to evolve data that, by definition, is immutable.

I won’t lie; migrations are never easy., even in relational databases. You always have to think about the following:

• What caused the change?

• What are the possible solutions?

• Is the change breaking?

• What to do with old data?

When working in event schema evolution, you must ask yourself the same questions. Based on the answers, you need to choose your strategy.

During the webinar, I showed simple techniques that should take you far enough:

• simple mapping scenarios, where serialiser features are good enough,

• upcasting and downcasting, so how to transform our events on the fly to the latest schema or to the schema that’s compatible with previous versions,

• explicit (de)serialisation to handle the payload transformation without additional magic,

• more advanced scenarios.

All of that was put into a broader context together with considerations on how to apply that:

• inside module,

• cross-module communication,

• business logic and projections,

• differences between environments like C#, Java, TypeScript,

• using EventStoreDB, Marten, but also messaging tooling.

In the end, in Grand Finale, we also discussed the trick of not needing to do versioning at all!

You can also read my articles:

• Simple patterns for events schema versioning

• How to (not) do the events versioning?

• Explicit events serialisation in Event Sourcing

• Fun with serial JSON

• Mapping event type by convention

• Event Versioning with Marten

• Let's take care of ourselves! Thoughts on compatibility

• Internal and external events, or how to design event-driven API

Source codes are available here:

• - C#,

  - Java,

  - Typescript.

Or just watch the webinar, as it’s all there and more!

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Webinars:

• #1 - From CRUD to Event Sourcing

• #2 - Keep your streams short! Or how to model Event-Sourced systems efficiently

• #3 - Implementing Distributed Processes

• #4 - From CRUD to CQRS in practice

• #5 - Architecture Weekly 100 Edition - Live Q&A

• #6 - Alexey Zimarev - You don't need an Event Sourcing framework. Or do you?

• #7 - Design and test Event-Driven projections and read models

• #8 - Slim down your aggregates!

• #9 - Radek Maziarka - Modularization with Event Storming Process Level

• #10 - PostgreSQL Superpowers in Practice

• #11 - Maciej "MJ" Jędrzejewski - Evolutionary Architecture: The What. The Why. The How.

• #12 - Jeremy D. Miller: Simplify your architecture with Wolverine

• #13 - Yves Goeleven - The Fantastic 9

• #14 - Mateusz Jendza: Why Verified Credentials is the Future of Digital Identity!

• #15 - Mário Bittencourt: Leveraging BPMN for Seamless Team Collaboration in Software Development

• Papers We Love #1 - Sagas (Hector Garcia-Molina, Kenneth Salem)

• #16 - Simple patterns for events schema versioning...