Question

One of the basic tenets of CQRS, as I understand it, is that commands should be behaviour-centric, and have a value in the business or the UL, and not data-centric, ie., CRUD. Instead of focusing on updating a customer, we have commands like CustomerHasMoved. What if you have CRUD screens which are there to correct certain data. For example, we need to change the name of a customer which is misspelled. This doesn t really have much value in the business. Should this just be under the umbrella of an UpdateCustomer command?

Answer 1

Actually, there could be various reasons to update the name of a customer. As you were saying, it could be misspelled or... you could get married and change your name to your husband s.

If you had only an UpdateCustomer command, you would loose the original intent and you would not be able to have different behaviours for each of them. If the name was misselled it could be as simple as updating the database, whereas if your customer got married you might need to notify the marketing departement so tthat they can offer a discount.

In the case that your entity is purely CRUD, that is there is no intent that you can associate with modifying the properties, then it s OK to have an UpdateEntityCommand. You can then transition slowly to something more task based

Answer 2

I just want to put a comment on this quickly as it popped up.

It is important to note that some objects are actually CRUD and thats ok. I may not really care why a name is changing in my domain where I ship products to people and only need that data to print mailing labels. The trick is in making behavior the default and THEN reverting to a CRUD interface once you are sure you really don t care about the reasons as opposed to vice versa.

Greg

Answer 3

CustomerHasMoved is the event that is fired after you have updated the customers location. This event updates the read databases/cache databases. The command from the gui should be MoveCustomer or something like that. I think I would put the update of the customer name in a command like UpdateCustomer.

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