list<intrusive_ptr<DocumentSource>> DocumentSourceChangeStream::createFromBson(
BSONElement elem, const intrusive_ptr<ExpressionContext>& expCtx) {
// TODO: Add sharding support here (SERVER-29141).
uassert(
40470, "The $changeStream stage is not supported on sharded systems.", !expCtx->inMongos);
uassert(40471,
"Only default collation is allowed when using a $changeStream stage.",
!expCtx->getCollator());
auto replCoord = repl::ReplicationCoordinator::get(expCtx->opCtx);
uassert(40573,
"The $changeStream stage is only supported on replica sets",
replCoord &&
replCoord->getReplicationMode() == repl::ReplicationCoordinator::Mode::modeReplSet);
Timestamp startFrom = replCoord->getMyLastAppliedOpTime().getTimestamp();
intrusive_ptr<DocumentSource> resumeStage = nullptr;
auto spec = DocumentSourceChangeStreamSpec::parse(IDLParserErrorContext("$changeStream"),
elem.embeddedObject());
if (auto resumeAfter = spec.getResumeAfter()) {
ResumeToken token = resumeAfter.get();
auto resumeNamespace = UUIDCatalog::get(expCtx->opCtx).lookupNSSByUUID(token.getUuid());
uassert(40615,
"The resume token UUID does not exist. Has the collection been dropped?",
!resumeNamespace.isEmpty());
startFrom = token.getTimestamp();
if (expCtx->needsMerge) {
DocumentSourceShardCheckResumabilitySpec spec;
spec.setResumeToken(std::move(token));
resumeStage = DocumentSourceShardCheckResumability::create(expCtx, std::move(spec));
} else {
DocumentSourceEnsureResumeTokenPresentSpec spec;
spec.setResumeToken(std::move(token));
resumeStage = DocumentSourceEnsureResumeTokenPresent::create(expCtx, std::move(spec));
}
}
const bool changeStreamIsResuming = resumeStage != nullptr;
auto fullDocOption = spec.getFullDocument();
uassert(40575,
str::stream() << "unrecognized value for the 'fullDocument' option to the "
"$changeStream stage. Expected \"default\" or "
"\"updateLookup\", got \""
<< fullDocOption
<< "\"",
fullDocOption == "updateLookup"_sd || fullDocOption == "default"_sd);
const bool shouldLookupPostImage = (fullDocOption == "updateLookup"_sd);
auto oplogMatch = DocumentSourceOplogMatch::create(
buildMatchFilter(expCtx->ns, startFrom, changeStreamIsResuming), expCtx);
auto transformation = createTransformationStage(elem.embeddedObject(), expCtx);
list<intrusive_ptr<DocumentSource>> stages = {oplogMatch, transformation};
if (resumeStage) {
stages.push_back(resumeStage);
}
auto closeCursorSource = DocumentSourceCloseCursor::create(expCtx);
stages.push_back(closeCursorSource);
if (shouldLookupPostImage) {
stages.push_back(DocumentSourceLookupChangePostImage::create(expCtx));
}
return stages;
}
