I’ve read about CQRS systems that maintain a simple key value store on the command side to represent an application’s state, and others that merely correlate messages (using some sort of saga) and utilise the query store to represent an applications state instead. Either way there’ll no doubt be a persistence technology involved with these … Read more
Commands and Events can be of very different concerns. They can be technical concerns, integration concerns, domain concerns… I assume that if you ask about domain, you’re implementing a domain model (maybe even with Domain Driven Design). If this is the case I’ll try to give you a really simplified response, so you can have … Read more
The framework relies heavily on eventsourcing, which means that all state changes are >written to the data store as events. “ This is completely untrue, it does not rely heavily on event-sourcing. One of the implementations for storing the aggregate in this framework use Event-Sourcing but you can easily use also the classes provided to … Read more
Event Sourcing is optional and in most cases complicates things more than it helps if introduced too early. Especially when transitioning from a legacy architecture and even more when the team has no experience with CQRS. Most of the advantages being attributed to ES can be obtained by storing your events in a simple Event … Read more
I agree with a number of the concepts presented in other responses, but I put them together in my code. First, I agree that using Value Objects for values that include behavior is a great way to encapsulate common business rules and an e-mail address is a perfect candidate. However, I tend to limit this … Read more
CQRS is all about fire-and-forget, and since GUIDs are very reliable (low risk of collision) there is no problem sending in a GUID that you generate your self. The steps would basically be: Create your command Generate and assign your identity (GUID) to it Fire the command Return the identity earlier generated Read more about … Read more
There’s a implementation here MarkNijhof. But after reading the documents from the CQRS Info site my favourite resource is Think Before Coding look at the post Tags. (http://thinkbeforecoding.com/) Some other useful resources… http://distributedpodcast.com/ http://www.udidahan.com/ http://abdullin.com/
Having Commands gives you the benefits of the good old Command pattern: you can parameterize an object, e.g. a UI element, with a Command to perform you can store a Command and execute it later, e.g. in a queue or a transaction log you can track which Commands you executed, giving you a foundation for … Read more
Here is my take on this. CQRS + ES can make things a lot simpler in complex software systems by having rich domain objects, simple data models, history tracking, more visibility into concurrency problems, scalability and much more. It does require a different way thinking about the systems so it could be difficult to find … Read more
What is a saga in contrast to a process manager? The intent of these patterns is different. A process manager is a workflow pattern which can, as you say, be built on top of a state machine. A process manager will retain state between messages, and will contain logic in order to determine which action … Read more