Get value from SPFieldUser with AllowMultipleValues fails only in a Timer Job - sharepoint-2010

Question

This one is weird.
I'm executing this code in a Timer Job in SharePoint 2010 ...
...
// Get the field by it's internal name
SPField field = item.Fields.GetFieldByInternalName(fieldInternalName);
if (field != null)
{
SPFieldUser userField = (SPFieldUser)field;
object value = null;
if (userField.AllowMultipleValues)
{
// Bug when getting field value in a timer job? Throws an ArgumentException
users = new SPFieldUserValueCollection(item.ParentList.ParentWeb, item[userField.Id].ToString());
}
else
{
// Get the value from the field, no exception
value = item[userField.Id];
}
}
...
This code works perfectly when run in a simple ConsoleApplication but when run in the context of a Timer Job in SharePoint 2010 it throws an ArgumentException in the line ...
users = new SPFieldUserValueCollection(item.ParentList.ParentWeb, item[userField.Id].ToString());
I've tried many variations to retreive a value from a SPFieldUser but all fail only when a Timer Job is executing it and the field has AllowMultipleValues property set to TRUE.
I have tried debugging with Reflector and it seems that the exception is being thrown here in SPListItem ...
public object this[Guid fieldId]
{
get
{
SPField fld = this.Fields[fieldId];
if (fld == null)
{
throw new ArgumentException();
}
return this.GetValue(fld, -1, false);
}
...
And this here would be the exception stack trace...
System.ArgumentException was caught
Message=Value does not fall within the expected range.
Source=Microsoft.SharePoint
StackTrace:
at Microsoft.SharePoint.SPFieldMap.GetColumnNumber(String strFieldName, Boolean bThrow)
at Microsoft.SharePoint.SPListItemCollection.GetColumnNumber(String groupName, Boolean bThrowException)
at Microsoft.SharePoint.SPListItemCollection.GetRawValue(String fieldname, Int32 iIndex, Boolean bThrow)
at Microsoft.SharePoint.SPListItem.GetValue(SPField fld, Int32 columnNumber, Boolean bRaw, Boolean bThrowException)
at Microsoft.SharePoint.SPListItem.get_Item(Guid fieldId)
at FOCAL.Point.Applications.Audits.AuditUtility.GetPeopleFromField(SPListItem item, String fieldInternalName)
Sighh... any thoughts?

Answer 1

This generally means that you have requested too many lookup fields in a single SPQuery which would cause too many self-joins of the true-lookup-table in the content database unless SharePoint Foundation throttled resources. There is a threshold setting that is at 8 lookups per query for ordinary users. Make sure your query only returns the necessary lookup or person/group fields. If you can't decrease the usage, then consider altering the threshold setting.