I am using WCF and peer mesh to get "real-time" updates from my server application to my clients.  For one of my operation contracts I wanted to return a typed datatable.  I struggled with this quite a bit and couldn't understand why since a datatable object is inherently serializable.

The problem turned out to be null values in some of the records.  If any of the rows in the datatable contain dbnulls then the receiving side just doesn't receive anything.  Basically WCF malfunctions.  An error is not thrown and when debugging from the sender side everything appears to be sent.  However nothing comes in on the receiving side of things.  This is actually the most frustrating part of WCF, often errors aren't thrown the thing just doesn't work.

Anyway, if you define your tables that you want to pass with WCF to disallow dbnull and provide default values for all the fields you will not have this problem.  That is what I did.  Unfortunately this changes my datatables a bit and I have to make sure that my application isn't check for dbnull to indicate an "unset value" when doing updates etc.  I am guessing that the issue is that dbnull is not serializable which is why it fails.

Hope this is a helpful hint for those struggling with sending datatables with WCF.

Sean