public SqlTableBase GetReferencedGroupSource (SqlGroupingSelectExpression groupingSelectExpression)
{
ArgumentUtility.CheckNotNull ("groupingSelectExpression", groupingSelectExpression);
SqlTableBase result;
if (_groupReferenceMapping.TryGetValue (groupingSelectExpression, out result))
return result;
var message = string.Format (
"No associated table found for grouping select expression '{0}'.",
FormattingExpressionTreeVisitor.Format (groupingSelectExpression));
throw new InvalidOperationException (message);
}