As more developers apply Command/Query Responsibility Segregation to their projects, many find that it INCREASES the complexity of their systems rather than decreasing it, often without any performance benefits either. Join Udi for a look at where you should, and more importantly SHOULDN'T be using CQRS in your projects.
Derek Comartin asked for questions about Event Sourcing and CQRS and took some of them to Greg Young for answers about frameworks, Legacy Systems, Use Cases, Projections, Eventual Consistency and Versioning.
The article discusses the development of a Read Model for a Bounded Context, which is a separate persistence store optimized for reading data. Data is inserted into the Read Model by using Event Handlers, which listen to events emitted from the Write Model after changes in Aggregate state. Nick implements a Bus to transport Commands and Events to appropriate Handlers. The article includes discussing how the Read Model can be made consistent with the Write Model.
How to signify acknowledgement, or negative-acknowledgement, of Commands when applying CQRS.
Whenever we send asynchronous messages and modify state in database within same action, we put ourselves at risk. The risk come from the possibility that state will be persisted and message will fail...
Engineers from Auto Trader explain how they use User behaviour to improve the quality of search results for customers. An interesting article exploring events, relays, derived data projections, Customer Data Platform and API gateways.
A quick and simple overview of what CQRS and Event Sourcing is.
Gently down the stream provides an introduction to event streaming - as a children's book! It isn't overly specific to Kafka making it a nice introduction even if you are planning on using a different message broker.
What are Repositories? Why should you treat them as collections? How should you interact with them, and should they create your entities? Shawn covers many of these topics to provide a solid introduction to the Repository pattern.
Apache Kafka is a cool product, but if you are thinking about using it for event sourcing Jesper Hammarbäck thinks you should think again.
In this article, Oskar takes us through his thought process and provides his answer to one of the most-asked questions regarding CQRS: can a Command return a value?
As we all know, naming things is one of the really hard problems in computer science. Maybe this is the reason the term “event” is used for what feels like at least twenty different concepts. It’s all too easy to get confused when people talk about Event Sourcing, Event Streaming, Event-Carried State Transfer, Notification Events, Domain Events, Fat Events, Event Storming and possibly yet other types of events. Serverless Functions - triggered by events, Apache Kafka users like to speak of events, as do those of the Axon framework - are they even meaning the same thing at all? And above all - why should I even bother with an Event-driven architecture, what are the benefits? Time for a proper clean-up. Let's start with a clear and bounded definition of events, and from there explore the patterns of using events in micro- and macro-architecture, their benefits as well as challenges. After the talk, participants will know what questions to ask if someone suggests to go event-driven, and will be able to assess the applicability of different approaches to their architectural tasks.
Event Modeling was coined by Adam Dymitruk by building on long-running process specifications that Greg Young used in CQRS/ES systems. Scott sits down with Adam to understand this process and how it makes your systems - and your life making those systems - easier to write, understand, and maintain.
A step-by-step overview of cqrs and event sourcing focusing on the flow from Command through to Read Model.
A quick step-by-step guide to building your own Aggregate Root for CQRS and Event Sourcing. With example C# code.
In this architecture lesson Mark Richards describes the CQRS pattern (Command Query Responsibility Segregation) and shows how it can be applied in a Microservices architecture.
Greg Young is an independent consultant and serial entrepreneur. He has 10-plus years of varied experience in computer science from embedded operating systems to business systems, and he brings a pragmatic and often unusual viewpoint to discussions.
Define a queryable replica that is kept up to date by subscribing to events published by the services that own the data.
CQRS (Command Query Responsibility Segregation) is the notion that you can use a different model to update information than the model you use to read information
After listening how the community has interpreted Command-Query Responsibility Segregation I think that the time has come for some clarification. Some have been tying it together to Event Sourcing. Most have been overlaying their previous layered architecture assumptions on it. Here I hope to identify CQRS itself, and describe in which places it can connect to other patterns.
The command query responsibility segregation (CQRS) pattern, derived from the principle of command-query separation, has been popularized by the domain-driven design community. CQRS architectures that use event sourcing save generated events in an append-only log called an event store. By using event sourcing, you can, among other benefits: Design applications to update a database and [...]
In this article, I introduce a form of Accidental Complexity I've been referring to as Accidental Intent Cancelling.