Answers

1. CQS stands for Command-Query Separation. It’s a software design principle that separates operations that change the state of an object (commands) from those that return data (queries). This helps in minimizing side effects and preventing unexpected changes in program behavior.
2. Yes, you can. The goal of the Mediator pattern is to mediate communication between colleagues.
3. In the original sense of CQS, no, a command can’t return a value. The idea is that a query reads data while commands mutate data. A command can return a value in a looser sense of CQS. For example, nothing stops a create command from returning the created entity partially or totally. You can always trade a bit of modularity for a bit of performance.
4. MediatR is a free, open source project licensed under Apache License 2.0.
5. Yes, you should. Using marker interfaces to add metadata is generally wrong. Nevertheless, you should analyze each use case individually, considering...