Practical Event Sourcing with Scala
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Practical Event Sourcing with Scala

A comprehensive example based on Scala, Play and Akka Streams

About the Book

This book takes a very practical and rather unusual approach towards the event sourcing architecture. Instead of diving into the DDD terminology, which is usually popular in the Enterprise, we will use this pattern to implement a typical Web application.

Instead of C# or Java, we will be using Scala as the backend language and JavaScript (ES6) as the frontend one. Along the way, we will also make use of some other supporting technologies such as Play, Akka Streams, Kafka, React (with Redux), Websockets and even Neo4J.

You don't need to be a Scala guru to understand code samples, but some familiarity with the syntax is required. If you're completely new to Scala, I highly recommend you go through the free sample of my other book - Modern Web Development with Scala. The PDF sample could be read in an hour, but it covers most widely used syntax constructs.

Which versions are used

The main examples use Scala 2.13 and Play 2.8. When additional libraries are needed, their latest versions are used.


My special thanks go to Tim Ruhland for his enormous help in eliminating typos and errors. The cover illustration was designed by Freepik

About the Author

Denis Kalinin
Denis Kalinin

Having started as a Java developer in a middle-sized enterprise company, over the course of my career I've worked in several different countries and gained quite a bit of experience. During the last eight years I've used a great number of libraries and frameworks from JavaServer Faces to React. 

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Table of Contents

  • Preface
  • Chapter 1. The initial project
    • Preparing the environment
    • Initializing the project
    • The backend part
    • The frontend part
  • Chapter 2. Handling simple events
    • Event sourcing basics
    • Preparing the event store
    • Working with log records
    • The read service
    • Akka Streams in 5 minutes
    • Updating the state with Akka Streams
    • Producing events
    • Implementing the controller
    • Learning React in 5 minutes
    • Managing tags with React
  • Chapter 3. Data processing pipeline
    • Introducing Kafka
    • Using Kafka from Scala
    • Server-sent events
    • Managing state with Redux
    • Implementing Kafka consumers
  • Chapter 4. Validating and querying data
    • Dealing with questions
    • Linking questions to users
    • Implementing server-side validation
    • Introducing Neo4J
    • The Cypher query language
    • Executing Neo4J statements
    • Rewriting the read service
    • Integrating user-related events
    • Initializing the state
  • Chapter 5. Frontend routing
    • Adding the question controller
    • Designing the views
    • Nested views
    • The Ask question view
    • Showing validation errors
    • The question list view
    • Confirmation service
    • Dealing with question threads
    • The question details view
    • Routing it all together
  • Chapter 6. Answers and upvotes
    • Answers and upvotes
    • Validating new event types
    • Adjusting the read state
    • Answers on the frontend
  • Chapter 7. Time travelling
    • Rewinding in chunks
    • Time travel dashboard
    • Using Websockets
  • Closing remarks
  • Appendix A. Source code

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