Since EF DB first generates it's entities automatically, I don't want to make changes inside the entities classes. I thought to create a computed fields inside VistaDB but I didn't find how to do it. Is it possible? Do you might have a better solution for this issue?
Simple and brilliant :-)
What most folks do in this situation is add a partial class file with the extra methods. This way you're not modifying the generated code (don't do that!) and you can add all kinds of extra stuff. We do this ourselves where we use EF within Loupe and when we've done client projects (where we typically use the Db First approach)