//The structure of result is a Filter, variable is current node, body is the match condition.
//Previous predicate build logic in XPathPatternBuilder is match from right to left, which have 2^n complexiy when have lots of position predicates. TFS #368771
//Now change the logic to: If predicates contains position/last predicates, given the current node, filter out all the nodes that match the predicates,
//and then check if current node is in the result set.
public QilNode BuildPredicates(QilNode nodeset, List <QilNode> predicates)
{
//convert predicates to boolean type
List <QilNode> convertedPredicates = new List <QilNode>(predicates.Count);
foreach (var predicate in predicates)
{
convertedPredicates.Add(XPathBuilder.PredicateToBoolean(predicate, _f, _predicateEnvironment));
}
QilLoop nodeFilter = (QilLoop)nodeset;
QilIterator current = nodeFilter.Variable;
//If no last() and position() in predicates, use nodeFilter.Variable to fixup current
//because all the predicates only based on the input variable, no matter what other predicates are.
if (_predicateEnvironment.numFixupLast == 0 && _predicateEnvironment.numFixupPosition == 0)
{
foreach (var predicate in convertedPredicates)
{
nodeFilter.Body = _f.And(nodeFilter.Body, predicate);
}
nodeFilter.Body = _predicateEnvironment.fixupVisitor.Fixup(nodeFilter.Body, current, null);
}
//If any preidcate contains last() or position() node, then the current node is based on previous predicates,
//for instance, a[...][2] is match second node after filter 'a[...]' instead of second 'a'.
else
{
//filter out the siblings
QilIterator parentIter = _f.For(_f.Parent(current));
QilNode sibling = _f.Content(parentIter);
//generate filter based on input filter
QilLoop siblingFilter = (QilLoop)nodeset.DeepClone(_f.BaseFactory);
siblingFilter.Variable.Binding = sibling;
siblingFilter = (QilLoop)_f.Loop(parentIter, siblingFilter);
//build predicates from left to right to get all the matching nodes
QilNode matchingSet = siblingFilter;
foreach (var predicate in convertedPredicates)
{
matchingSet = XPathBuilder.BuildOnePredicate(matchingSet, predicate, /*isReverseStep*/ false,
_f, _predicateEnvironment.fixupVisitor,
ref _predicateEnvironment.numFixupCurrent, ref _predicateEnvironment.numFixupPosition, ref _predicateEnvironment.numFixupLast);
}
//check if the matching nodes contains the current node
QilIterator matchNodeIter = _f.For(matchingSet);
QilNode filterCurrent = _f.Filter(matchNodeIter, _f.Is(matchNodeIter, current));
nodeFilter.Body = _f.Not(_f.IsEmpty(filterCurrent));
//for passing type check, explicit say the result is target type
nodeFilter.Body = _f.And(_f.IsType(current, nodeFilter.XmlType), nodeFilter.Body);
}
SetPriority(nodeset, 0.5);
return(nodeset);
}