Idempotent 'create' commands

Imported from Google Groups
1

My application needs its command interface to be idempotent.
For update commands I see no other option other than allowing commands to be replayed - we will have to live with multiple updated events each simply repeating the previous update. But for create commands - what should I do? What is the CQRS best practise?

I can use the repo to load the aggregate before I fire the create command, and catch the AggregateNotFound exception, but I would rather not have my logs littered with stack traces...

Or should I use the query model to check for the pre-existence of the aggregate?

Regards

Phil

2

Have decided to use the Command model to check for pre-existence, rather than create a further dependency on the Query model.
But would still be interested to hear how others have approached this...

3

This concern is part of your domain. Create an interface that uses the query model from the command handler. You may also want to review the Reservation design pattern.