Strange SPQuery Behaviour

I have been working on a very simple web part for a long time, the actual code for the web part takes less than an hour to write and merely displays a colour coded letter based on a query from a SharePoint list taking the date as a parameter.

It has taken a long time because of some strange behaviour with the SPQuery object, initially there was a problem with every row in the table being returned irrespective of the query, the odd thing was that if you ran the query in U2U CAML Query Builder it worked and the SPListItemCollection.count method would return 1 suggesting the query was working.

After adding a copious number of debugging command, I built up a pattern of what was happening and why. However no matter what I changed it either threw an exception as expected or returned all of the rows. I started commenting out lines of code one at a time trying to find the culprit, eventually moving on to commenting out the Debug.WriteLine statements, until I hit this line:

Debug.WriteLine(fetchCurrentWeek.ViewXml);

After commenting out this line the whole thing worked perfectly, I can put the date forward on the server and it will update I can change the source table and it reflects the changes after the cache has been cleared. I have looked over the Microsoft Documentation on SPQuery.ViewXml and can’t find any reference to it actually affecting the functionality of the object. I have included my code at the end of this post for anyone to see, feel free to experiment with it. If you figure it out please do let me know.

using (SPWeb site = SPControl.GetContextSite(Context).OpenWeb())
{
 SPList weekList = site.GetList(this.SourceList);
 // sharepoint requires that we use a ISO8601 DateTime string,
 // generate it and insert it into the query
 string mondayOfCurrentWeek = SPUtility.CreateISO8601DateTimeFromSystemDateTime(GetMondayOfCurrentWeek().Date);
 StringBuilder camlBuilder = new StringBuilder();
 camlBuilder.AppendLine  ("<Where>");
 camlBuilder.AppendLine  ("  <Eq>");
 camlBuilder.AppendLine  ("    <FieldRef Name='WeekCommencing'/>");
 camlBuilder.AppendFormat("    <Value Type='DateTime'>{0}</Value>\r\n", mondayOfCurrentWeek);
 camlBuilder.AppendLine  ("  </Eq>");
 camlBuilder.AppendLine  ("</Where>");

 string getWeekCAML = camlBuilder.ToString();
 SPQuery fetchCurrentWeek = new SPQuery(weekList.DefaultView);
 // fetch all of the matching weeks from the table
 fetchCurrentWeek.Query = getWeekCAML;
 SPListItemCollection matchingWeeks = weekList.GetItems(fetchCurrentWeek); // the results of the query should only ever equal 1 if it dosn't something is wrong
 if (matchingWeeks.Count == 1)
 {
  SPListItem week = (SPListItem)matchingWeeks\[0\];
  WeekType = week\["Week Type"\].ToString();
  WeekType = SPEncode.HtmlEncode(WeekType); // HtmlEncode the result to make sure it dosn't contain any nastys
  String WeekNumber = week\["Week Number"\].ToString();
  WeekNumber = SPEncode.HtmlEncode(WeekNumber);
  Debug.WriteLine(String.Format(CultureInfo.InvariantCulture, "\[WeekWidget\] Found record for {0} as Week {1} - Number {2}", mondayOfCurrentWeek, WeekType, WeekNumber));
  // cache the WeekType for 7 days from midnight on Monday as this is when the changeover between weeks happenswou
  Context.Cache.Insert(CACHE\_WEEKTYPE, WeekType, null, GetMondayOfCurrentWeek().AddDays(7), TimeSpan.Zero);
 } // end if matchingWeeks count equal to 1
 else
 {
  // more than one week matched, we can not determine the output correctly
  ErrorText.Text = "More than one week matched in the table, please check the table.";
  LogEvent("More than one week (" + matchingWeeks.Count.ToString() + ") matched in the table, please check the table.");
 } // end else

Happy Hunting