To be honest, I thought that my previous post would be the last in the CQRS/ES series, but I forgot to discuss one more thing related to that topic. Many developers don’t know how we should handle the following scenario in our systems:   „During the creation of user’s new account I would like to verify rather a username is unique in the whole database. Should I use Event Store or Read Database for a query? Where should I check that?”   Seriously, that question is one of the most popular topics connected ...