Testing Columns in a DataSet
I ran into a nasty little surprise the other day. I was writing some code to see if a Project has a WSS site associated with it. So here is the code that I’ve cut down for brevity:
private string GetWSSSite(Guid projectGuid)
{
ProjectWS.ProjectDataSet pds =
ProjWebSvc.ReadProject(projectGuid,
ProjectWS.DataStoreEnum.PublishedStore);
ProjectWS.ProjectDataSet.ProjectRow pr = pds.Project[0];
string WSSSite = pr.WPROJ_STS_SUBWEB_NAME;
if (WSSSite.Length == 0)
return String.Empty;
else
return WSSSite;
}
Essentially I read the project, and then either pass back the subweb name or an empty string. The only problem was the routine was throwing an exception. I bet you can’t guess which line was throwing the exception…. give up? It was the assignment of the WSSSite. I was getting a System.Data.StrongTyping exception. When I started to debug and dig it thing became a little clearer. It seems I ran across a project that did not have a subweb associated with it. Since the DataSet is built directly from the database tables, the column WPROJ_STS_SUBWEB_NAME was DBNull. The DBNull brought on the StrongTyping exception. To work around this I modified the code as follows:
private string GetWSSSite(Guid projectGuid)
{
try
{
ProjectWS.ProjectDataSet pds =
ProjWebSvc.ReadProject(projectGuid,
ProjectWS.DataStoreEnum.PublishedStore);
ProjectWS.ProjectDataSet.ProjectRow pr = pds.Project[0];
return pr.WPROJ_STS_SUBWEB_NAME;
}
catch (System.Data.StrongTypingException ex)
{
return String.Empty;
}
}
So the lesson here is when testing column value be careful they may throw an exception. To get a better idea of where you may encounter problems you can go into debug mode and put a breakpoint after you fill the DataSet. If you look through the row in watch mode you will see a number of exceptions. See the attached picture for illustration.
Also note in the code above you should be testing for exceptions from the ReadProject call, but I removed that to better illustrate the column exception.
