[Masterclass] Building an Event-Sourced System in .NET with Marten | Hannes Lowette

Most systems built on traditional CRUD models only store the current state of data, discarding the valuable history that led there. This creates challenges: we can’t easily see how data looked at any point in time, nor can we replay history to test new features against past events.

Event sourcing addresses these problems by capturing every event that leads to the current state. This not only allows us to reconstruct history and re-derive state but also opens the door to powerful new capabilities in system design.

In this hands-on workshop, you’ll dive deep into the concepts of event sourcing while implementing a fully event-sourced system in C#. Guided by Hannes Lowette, you’ll work with Marten, a production-ready, open-source event sourcing framework for .NET, to see how theory translates into practice.

Goals & Outcomes

By the end of this masterclass, participants will:

• Understand the core principles of event sourcing and how it differs from CRUD-based systems.
• Learn how to capture and persist domain events effectively.
• Be able to replay event streams to rebuild state and test new features against historical data.
• Gain hands-on experience building an event-sourced system in C# using Marten.
• Recognize the benefits and trade-offs of event sourcing in real-world distributed systems.
• Leave with practical implementation patterns to apply in their own projects.

Equipment & Prerequisites

Participants should bring:

• A laptop with admin rights to install/run software.
• .NET 8 SDK (or the latest stable version) installed.
• A modern IDE or editor (Visual Studio, Rider, or VS Code recommended).
• Docker installed and running (for database setup).
• A basic understanding of C# and .NET development.
• Familiarity with databases and general system design concepts will be helpful but not strictly required.

Speaker: Hannes Lowette

Head of Learning & Development — Microsoft MVP

Hannes is a developer, coach, and father of three. In .NET development, he has always had a passion for performance, databases, distributed systems, and large-scale applications. Above all, he enjoys playing devil’s advocate in technical discussions, often drawing the famous “it depends” card.

As a coach, Hannes is enthusiastic about knowledge sharing, personal growth, and career building, all while emphasizing sustainable pace.

In his free time, when he’s not building LEGO® castles with his kids, he enjoys guitar building, chess, poker, whisky tasting, and all-around geeky hobbies. You might also spot him performing on stage at PubConf or jamming with Dylan Beattie & the Linebreakers.