In a RavenDB ASP.NET MVC app I was recently working on, I was constantly seeing good ol’ System.FormatException – “Input string was not in a correct format”.

My entities all use ints for their Ids.

After a while I noticed (via the RavenDB Management Console) that my entities had Ids like “tab/123”, but previously the Ids were like “tab-123”.

The problem turned out to be that I had accidentally removed this line while doing some refactoring:

documentStore.Conventions.IdentityPartsSeparator = "-";

Once I put that back in I stopped seeing the System.FormatException and all was right in the world.