Domain queries in CQRS

Question

We are trying out CQRS. We have a validation situation where a CustomerService (domain service) needs to know whether or not a Customer exists. Customers are unique by their

Answer 1

Hope I am not too late...but we faced a similar situation in our project, we actually intercept the command executor and attach it with the set of rules created for that command, which in turn uses a query to fetch the data.

So in this case, We can have a class by the name, CustomerEmailMustBeUniqueRule which is fetched by the RuleEngine when the command "RegisterCustomerCommand" is about to be executed by RegisterCustomerCommandExecutor. This rule class has the responsibility to query the database to find if the email id exist and stop the execution by raising the invalid flag...