prevent double calendar entry on same date and time programmatically

Question

Can this be done programatically while saving a recurring entry?

Answer 1

Yes, it can be done but unfortunately it requires either a lot of code or the willingness to access unsupported parts of SharePoint.

Microsoft has marked both the class Microsoft.SharePoint.ApplicationPages.Calendar.OverbookChecker and the usefull method static bool IsOverbook(SPList list, string currentId, SPItem target, bool isTargetRecurrence) as being Internal to Microsoft.SharePoint