PlanCacheKey PlanCache::computeKey(const CanonicalQuery& cq) const {
StringBuilder keyBuilder;
encodeKeyForMatch(cq.root(), &keyBuilder);
encodeKeyForSort(cq.getQueryRequest().getSort(), &keyBuilder);
encodeKeyForProj(cq.getQueryRequest().getProj(), &keyBuilder);
return keyBuilder.str();
}
/**
* Traverses expression tree pre-order.
* Appends an encoding of each node's match type and path name
* to the output stream.
*/
void PlanCache::encodeKeyForMatch(const MatchExpression* tree,
StringBuilder* keyBuilder) const {
// Encode match type and path.
*keyBuilder << encodeMatchType(tree->matchType());
encodeUserString(tree->path(), keyBuilder);
// GEO and GEO_NEAR require additional encoding.
if (MatchExpression::GEO == tree->matchType()) {
encodeGeoMatchExpression(static_cast<const GeoMatchExpression*>(tree), keyBuilder);
}
else if (MatchExpression::GEO_NEAR == tree->matchType()) {
encodeGeoNearMatchExpression(static_cast<const GeoNearMatchExpression*>(tree),
keyBuilder);
}
// Encode indexability.
const IndexabilityDiscriminators& discriminators =
_indexabilityState.getDiscriminators(tree->path());
if (!discriminators.empty()) {
*keyBuilder << kEncodeDiscriminatorsBegin;
// For each discriminator on this path, append the character '0' or '1'.
for (const IndexabilityDiscriminator& discriminator : discriminators) {
*keyBuilder << discriminator(tree);
}
*keyBuilder << kEncodeDiscriminatorsEnd;
}
// Traverse child nodes.
// Enclose children in [].
if (tree->numChildren() > 0) {
*keyBuilder << kEncodeChildrenBegin;
}
// Use comma to separate children encoding.
for (size_t i = 0; i < tree->numChildren(); ++i) {
if (i > 0) {
*keyBuilder << kEncodeChildrenSeparator;
}
encodeKeyForMatch(tree->getChild(i), keyBuilder);
}
if (tree->numChildren() > 0) {
*keyBuilder << kEncodeChildrenEnd;
}
}
