I think my question has just been solved by another article, Clarified CQRS by Udi Dahan. The section “Commands and Validation” starts as follows: Commands and Validation In thinking through what could make a command fail, one topic that comes up is validation. Validation is different from business rules in that it states a context-independent … Read more
You’re on the right lines with or a mockup – you need to mock the IMediator There’s a few mocking libraries out there: Moq FakeItEasy NSubstitute Moq is one of the most popular, so, using your test as an example: [Fact] public async void UpdateCustomerCommand_CustomerDataUpdatedOnDatabase() { //Arrange var mediator = new Mock<IMediator>(); UpdateCustomerCommand command = … Read more
Yes, event sourcing is like a transaction log for your domain objects and the transaction log is the authoritative source of all of your data. You might have copies of the data in other forms designed for easy querying but they’re merely copies that can be deleted and rebuilt at any time. The transaction log … Read more
NEventStore is a persistence agnostic event sourcing library for .NET with multiple storage options such as relational and document databases. EventStoreDB is a newer and high performing event sourcing solution with its own persistence engine and API’s for multiple protocols and languages. It has open source and commercial options. As far as I know you … Read more
Please take a look at my DDDsample.Net project on CodePlex. The GUI is implemented using ASP.NET MVC while the business logic using DDD practices in 4 different variants: classic (no CQRS) CQRS with two NHIbernate relational data stores CQRS with LINQ to SQL on reporting side CQRS with Event Sourcing on command side
Yeah, there’s a confusion that arises. Here’s how it happens: First, in order to really help new people understand what CQRS is all about, and to really drive home how it differs from the typical layered architecture, people say things like, “Your view models can be completely flat”, and “You should have one table per … Read more
The easiest way to generate a task based UI is to protect all attributes/properties of your models. i.e. remove all setters. From this (pseudo code): public class TodoTask { public Date getDateAssigned(); public void setDateAssigned(Date); public string getAssignedTo(); public void setAssignedTo(string); } to this: public class TodoTask { public Date getDateAssigned(); public string getAssignedTo(); public … Read more
The solution I went with was to add a System aggregate root that could maintain a list of the current Facility names. When creating a new Facility, I use the System aggregate (only one System as a global object / singleton) as a factory for it. If the given facility name already exists, then it … Read more
Personally I think there’s nothing wrong with looking up the user’s name from within the event handler. But if you’re in a position where you can’t query the name from the User’s read model then I’d introduce an additional event handler to QuestionEventsHandler, to handle the UserRegistered event. That way the QuestionEventsHandler could maintain its … Read more