A really new way to look at software development in 2025 and beyond

Understanding Eventsourcing

PLANNING AND IMPLEMENTING SCALABLE SYSTEMS WITH EVENT MODELING AND EVENTSOURCING.

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"The first book to combine Event Modeling, Eventsourcing and Vertical Slice Architectures in one consistent software process."
Understanding Eventsourcing Book Cover
Martin Dilger

Why This Book?

I started to work on Software Projects around 2005. I went into professional development in 2008 and naturally evolved into the role of an IT Architect over the years. But something always felt off.
No matter how hard we tried, Architectures seemed to converge into this big ball of mud.
Not immediately, but steadily over the years.
Agile did not help. SOA certainly did not help. Microservices did not help. And AI also does not help.
I was pretty disappointed.
Everything changed when I discovered Event Modeling in 2021.
But learning Event Modeling, Event Sourcing, and Vertical Slice Architectures took an unbelievable amount of time and energy.
There is simply not a lot of information available. Especially when it comes down to building these systems.
Weeks went into months. And months into years.
I always waited for someone to put all together. Someone to confirm what I thought was the way forward.
Nobody did. So I wrote on LinkedIn in July 2024, simply asking, "Should I write it?"
The response was huge. So I started writing and finished the book in 3 months. And there was always this one thing on my mind - I wanted to write the book I so desperately needed 5 years ago.
Here it is.

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"This is not just another technical book—it’s a roadmap to more predictable, maintainable, and successful software projects. Martin Dilger has created an invaluable resource that I believe will influence how we approach software development for years to come."

- Gabriel N. Schenker

"By reading this book, you won’t just learn new techniques — you’ll transform the way you approach software development. You’ll gain clear, actionable steps to solve problems, communicate with unprecedented clarity, and estimate projects more accurately. In essence, you’ll be equipped to dismantle complexity and foster collaboration like never before."

- Adam Dymitruk

"Focusing on a practical implementation really worked for me. I appreciate the work you have done here."

- Gary Craine

"Highly recommended reading"

- Michael Plagge

"Thanks for writing the book, it will save me so much time and toil. I really like the Todo pattern to simplify the Saga. Also using an aggregate for uniqueness check is very nice."

- William Power

"The book is packed with knowledge and provides concrete example implementations. It advances the entire topic and makes it easier for developers to access. I can only recommend it."

- Sebastian Bortz

"The book is really great, practical, easy to read !"

- Vincent Vermesh

"I just finished reading Part 1 of your book, and I’m thrilled. The book has truly captivated me—I can’t stop reading!"

- Domenic Cassisi

Table of Contents

    • Foreword by Adam Dymitruk
    • Foreword by Gabriel N. Schenker
    • Why I Care
    • Foundations
    • Why You Should Care

    Part I: Foundations

    • 1.Event Sourcing - What Is It?
    • 2.Planning Systems Using Event Modeling
    • 3.CQRS, Concurrency, (Eventual) Consistency
    • 4.Internal vs. External Data
    • 5.The Anatomy of an Event-Sourced Application
    • 6.Event Streaming, Event Sourcing, and Stream Design
    • 7.Domain-Driven Design
    • 8.Sagas - Handling Transactions in Distributed Systems
    • 9.Vertical Slicing

    Part II: Modeling the System

    • 10.Modeling the System
    • 11.Brainstorming
    • 12.Modeling Use Cases with Wireframes
    • 13."Given / When / Then" Scenarios
    • 14.Use Case: Clear Cart
    • 15.Use Case: Submit Cart
    • 16.Use Case: Inventory Changed
    • 17.Use Case: Price Changed
    • 18.Structuring an Event Model

    Part III: From Zero to Running Software

    • 19.From Zero to Running Software
    • 20.Technology Stack
    • 21.Brief Introduction to Axon
    • 22.Implementing the First Slice - "Add Item"
    • 23.Implementing State View Slices Using Live-Projections
    • 24.Implementing Remove-Item and Clear-Cart
    • 25.Example Integration with Apache Kafka and Translations
    • 26.Implementing a Database Projection for Inventories
    • 27.Implementing Automations
    • 28.Submitting the Cart
    • 29.Handling Breaking Changes

    Part IV: Implementation Patterns

    • 30.Implementation Patterns
    • 31.What This Part Is About
    • 32.Pattern: Database Projected Read Model
    • 33.Pattern: Live Model
    • 34.Pattern: The (Partially) Synchronous Projection
    • 35.Pattern: The Logic Read Model
    • 36.Pattern: Snapshots
    • 37.Pattern: "Processor-TODO-List" Pattern
    • 38.Pattern: The Reservation Pattern
    • 39.Where to Go From Here?
    • 40.Notes
Cover for Ebook

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Understanding Eventsourcing

THE MISSING CHAPTERS

Buy the book on Leanpub to get immediate access to all new chapters

"We are not done yet. One new chapter added every 2 weeks (only on Leanpub)."

Next chapter in:
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missing chapters planned

    • 1. Handling Metadata
    • 2. Modelling & Implementing Security
    • 3. GDPR - Handling sensitive data
    • 4. Internal vs. External Data
    • 5. Rewriting History
    • 6. Building the UI for an eventsourced System
    • 7. Functional Modelling with the Decider Pattern
    • 8. API-Design & Eventsourcing
    • 9. Legacy Systems & Eventsourcing

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Technologies used in the book

The book is hands-on and guides you from the first idea and the first requirement to a complete and running implementation, showing you step by step how I do it on the way.
The ideas in the book are implementation agnostic and can be translated to any language or technology stack.

Happy Eventsourcerers