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/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#include "mongo/db/pipeline/document_source_limit.h"
#include "mongo/platform/basic.h"
#include "mongo/db/pipeline/document_source_unwind.h"
#include "mongo/db/exec/document_value/document.h"
#include "mongo/db/exec/document_value/value.h"
#include "mongo/db/jsobj.h"
#include "mongo/db/matcher/expression_algo.h"
#include "mongo/db/pipeline/document_source_sort.h"
#include "mongo/db/pipeline/expression.h"
#include "mongo/db/pipeline/lite_parsed_document_source.h"
namespace mongo {
using boost::intrusive_ptr;
using std::string;
using std::vector;
/** Helper class to unwind array from a single document. */
class DocumentSourceUnwind::Unwinder {
public:
Unwinder(const FieldPath& unwindPath,
bool preserveNullAndEmptyArrays,
const boost::optional<FieldPath>& indexPath,
bool strict);
/** Reset the unwinder to unwind a new document. */
void resetDocument(const Document& document);
/**
* @return the next document unwound from the document provided to resetDocument(), using
* the current value in the array located at the provided unwindPath.
*
* Returns boost::none if the array is exhausted.
*/
DocumentSource::GetNextResult getNext();
private:
// Tracks whether or not we can possibly return any more documents. Note we may return
// boost::none even if this is true.
bool _haveNext = false;
// Path to the array to unwind.
const FieldPath _unwindPath;
// Documents that have a nullish value, or an empty array for the field '_unwindPath', will pass
// through the $unwind stage unmodified if '_preserveNullAndEmptyArrays' is true.
const bool _preserveNullAndEmptyArrays;
// If set, the $unwind stage will include the array index in the specified path, overwriting any
// existing value, setting to null when the value was a non-array or empty array.
const boost::optional<FieldPath> _indexPath;
// Specifies if input to $unwind is required to be an array.
const bool _strict;
Value _inputArray;
MutableDocument _output;
// Document indexes of the field path components.
vector<Position> _unwindPathFieldIndexes;
// Index into the _inputArray to return next.
size_t _index = 0;
};
DocumentSourceUnwind::Unwinder::Unwinder(const FieldPath& unwindPath,
bool preserveNullAndEmptyArrays,
const boost::optional<FieldPath>& indexPath,
bool strict)
: _unwindPath(unwindPath),
_preserveNullAndEmptyArrays(preserveNullAndEmptyArrays),
_indexPath(indexPath),
_strict(strict) {}
void DocumentSourceUnwind::Unwinder::resetDocument(const Document& document) {
// Reset document specific attributes.
_output.reset(document);
_unwindPathFieldIndexes.clear();
_index = 0;
_inputArray = document.getNestedField(_unwindPath, &_unwindPathFieldIndexes);
_haveNext = true;
}
DocumentSource::GetNextResult DocumentSourceUnwind::Unwinder::getNext() {
// WARNING: Any functional changes to this method must also be implemented in the unwinding
// implementation of the $lookup stage.
if (!_haveNext) {
return GetNextResult::makeEOF();
}
// Track which index this value came from. If 'includeArrayIndex' was specified, we will use
// this index in the output document, or null if the value didn't come from an array.
boost::optional<long long> indexForOutput;
uassert(
5858203, "an array is expected", (_strict && _inputArray.getType() == Array) || !_strict);
if (_inputArray.getType() == Array) {
const size_t length = _inputArray.getArrayLength();
invariant(_index == 0 || _index < length);
if (length == 0) {
// Preserve documents with empty arrays if asked to, otherwise skip them.
_haveNext = false;
if (!_preserveNullAndEmptyArrays) {
return GetNextResult::makeEOF();
}
_output.removeNestedField(_unwindPathFieldIndexes);
} else {
// Set field to be the next element in the array. If needed, this will automatically
// clone all the documents along the field path so that the end values are not shared
// across documents that have come out of this pipeline operator. This is a partial deep
// clone. Because the value at the end will be replaced, everything along the path
// leading to that will be replaced in order not to share that change with any other
// clones (or the original).
_output.setNestedField(_unwindPathFieldIndexes, _inputArray[_index]);
indexForOutput = _index;
_index++;
_haveNext = _index < length;
}
} else if (_inputArray.nullish()) {
// Preserve a nullish value if asked to, otherwise skip it.
_haveNext = false;
if (!_preserveNullAndEmptyArrays) {
return GetNextResult::makeEOF();
}
} else {
// Any non-nullish, non-array type should pass through.
_haveNext = false;
}
if (_indexPath) {
_output.getNestedField(*_indexPath) =
indexForOutput ? Value(*indexForOutput) : Value(BSONNULL);
}
return _haveNext ? _output.peek() : _output.freeze();
}
DocumentSourceUnwind::DocumentSourceUnwind(const intrusive_ptr<ExpressionContext>& pExpCtx,
const FieldPath& fieldPath,
bool preserveNullAndEmptyArrays,
const boost::optional<FieldPath>& indexPath,
bool strict)
: DocumentSource(kStageName, pExpCtx),
_unwindPath(fieldPath),
_preserveNullAndEmptyArrays(preserveNullAndEmptyArrays),
_indexPath(indexPath),
_unwinder(new Unwinder(fieldPath, preserveNullAndEmptyArrays, indexPath, strict)) {}
REGISTER_DOCUMENT_SOURCE(unwind,
LiteParsedDocumentSourceDefault::parse,
DocumentSourceUnwind::createFromBson,
AllowedWithApiStrict::kAlways);
const char* DocumentSourceUnwind::getSourceName() const {
return kStageName.rawData();
}
intrusive_ptr<DocumentSourceUnwind> DocumentSourceUnwind::create(
const intrusive_ptr<ExpressionContext>& expCtx,
const string& unwindPath,
bool preserveNullAndEmptyArrays,
const boost::optional<string>& indexPath,
bool strict) {
intrusive_ptr<DocumentSourceUnwind> source(
new DocumentSourceUnwind(expCtx,
FieldPath(unwindPath),
preserveNullAndEmptyArrays,
indexPath ? FieldPath(*indexPath) : boost::optional<FieldPath>(),
strict));
return source;
}
DocumentSource::GetNextResult DocumentSourceUnwind::doGetNext() {
auto nextOut = _unwinder->getNext();
while (nextOut.isEOF()) {
// No more elements in array currently being unwound. This will loop if the input
// document is missing the unwind field or has an empty array.
auto nextInput = pSource->getNext();
if (!nextInput.isAdvanced()) {
return nextInput;
}
// Try to extract an output document from the new input document.
_unwinder->resetDocument(nextInput.releaseDocument());
nextOut = _unwinder->getNext();
}
return nextOut;
}
DocumentSource::GetModPathsReturn DocumentSourceUnwind::getModifiedPaths() const {
std::set<std::string> modifiedFields{_unwindPath.fullPath()};
if (_indexPath) {
modifiedFields.insert(_indexPath->fullPath());
}
return {GetModPathsReturn::Type::kFiniteSet, std::move(modifiedFields), {}};
}
bool DocumentSourceUnwind::canPushSortBack(const DocumentSourceSort* sort) const {
// If the sort has a limit, we should also check that _preserveNullAndEmptyArrays is true,
// otherwise when we swap the limit and unwind, we could end up providing fewer results to the
// user than expected.
if (!sort->hasLimit() || _preserveNullAndEmptyArrays) {
auto unwindPath = _unwindPath.fullPath();
// Checks if any of the $sort's paths depend on the unwind path (or vice versa).
SortPattern sortKeyPattern = sort->getSortKeyPattern();
bool sortPathMatchesUnwindPath =
std::any_of(sortKeyPattern.begin(), sortKeyPattern.end(), [&](auto& sortKey) {
// If 'sortKey' is a $meta expression, we can do the swap.
if (!sortKey.fieldPath)
return false;
return expression::bidirectionalPathPrefixOf(unwindPath,
sortKey.fieldPath->fullPath());
});
return !sortPathMatchesUnwindPath;
}
return false;
}
bool DocumentSourceUnwind::canPushLimitBack(const DocumentSourceLimit* limit) const {
// If _smallestLimitPushedDown is boost::none, then we have not yet pushed a limit down. So no
// matter what the limit is, we should duplicate and push down. Otherwise we should only push
// the limit down if it is smaller than the smallest limit we have pushed down so far.
return !_smallestLimitPushedDown || limit->getLimit() < _smallestLimitPushedDown.get();
}
Pipeline::SourceContainer::iterator DocumentSourceUnwind::doOptimizeAt(
Pipeline::SourceContainer::iterator itr, Pipeline::SourceContainer* container) {
tassert(5482200, "DocumentSourceUnwind: itr must point to this object", *itr == this);
if (std::next(itr) == container->end()) {
return container->end();
}
// If the following stage is $sort (on a different field), push before $unwind.
auto next = std::next(itr);
auto nextSort = dynamic_cast<DocumentSourceSort*>(next->get());
if (nextSort && canPushSortBack(nextSort)) {
// If this sort is a top-k sort, we should add a limit after the unwind so that we preserve
// behavior and not provide more results than requested.
if (nextSort->hasLimit()) {
container->insert(
std::next(next),
DocumentSourceLimit::create(nextSort->getContext(), nextSort->getLimit().get()));
}
std::swap(*itr, *next);
return itr == container->begin() ? itr : std::prev(itr);
}
// If _preserveNullAndEmptyArrays is true, and unwind is followed by a limit, we can add a
// duplicate limit before the unwind to prevent sources further down the pipeline from giving us
// more than we need.
auto nextLimit = dynamic_cast<DocumentSourceLimit*>(next->get());
if (nextLimit && _preserveNullAndEmptyArrays && canPushLimitBack(nextLimit)) {
_smallestLimitPushedDown = nextLimit->getLimit();
auto newStageItr = container->insert(
itr, DocumentSourceLimit::create(nextLimit->getContext(), nextLimit->getLimit()));
return newStageItr == container->begin() ? newStageItr : std::prev(newStageItr);
}
return std::next(itr);
}
Value DocumentSourceUnwind::serialize(boost::optional<ExplainOptions::Verbosity> explain) const {
return Value(DOC(getSourceName() << DOC(
"path" << _unwindPath.fullPathWithPrefix() << "preserveNullAndEmptyArrays"
<< (_preserveNullAndEmptyArrays ? Value(true) : Value())
<< "includeArrayIndex"
<< (_indexPath ? Value((*_indexPath).fullPath()) : Value()))));
}
DepsTracker::State DocumentSourceUnwind::getDependencies(DepsTracker* deps) const {
deps->fields.insert(_unwindPath.fullPath());
return DepsTracker::State::SEE_NEXT;
}
intrusive_ptr<DocumentSource> DocumentSourceUnwind::createFromBson(
BSONElement elem, const intrusive_ptr<ExpressionContext>& pExpCtx) {
// $unwind accepts either the legacy "{$unwind: '$path'}" syntax, or a nested document with
// extra options.
string prefixedPathString;
bool preserveNullAndEmptyArrays = false;
boost::optional<string> indexPath;
if (elem.type() == Object) {
for (auto&& subElem : elem.Obj()) {
if (subElem.fieldNameStringData() == "path") {
uassert(28808,
str::stream() << "expected a string as the path for $unwind stage, got "
<< typeName(subElem.type()),
subElem.type() == String);
prefixedPathString = subElem.str();
} else if (subElem.fieldNameStringData() == "preserveNullAndEmptyArrays") {
uassert(28809,
str::stream() << "expected a boolean for the preserveNullAndEmptyArrays "
"option to $unwind stage, got "
<< typeName(subElem.type()),
subElem.type() == Bool);
preserveNullAndEmptyArrays = subElem.Bool();
} else if (subElem.fieldNameStringData() == "includeArrayIndex") {
uassert(28810,
str::stream() << "expected a non-empty string for the includeArrayIndex "
" option to $unwind stage, got "
<< typeName(subElem.type()),
subElem.type() == String && !subElem.String().empty());
indexPath = subElem.String();
uassert(28822,
str::stream() << "includeArrayIndex option to $unwind stage should not be "
"prefixed with a '$': "
<< (*indexPath),
(*indexPath)[0] != '$');
} else {
uasserted(28811,
str::stream() << "unrecognized option to $unwind stage: "
<< subElem.fieldNameStringData());
}
}
} else if (elem.type() == String) {
prefixedPathString = elem.str();
} else {
uasserted(
15981,
str::stream()
<< "expected either a string or an object as specification for $unwind stage, got "
<< typeName(elem.type()));
}
uassert(28812, "no path specified to $unwind stage", !prefixedPathString.empty());
uassert(28818,
str::stream() << "path option to $unwind stage should be prefixed with a '$': "
<< prefixedPathString,
prefixedPathString[0] == '$');
string pathString(Expression::removeFieldPrefix(prefixedPathString));
return DocumentSourceUnwind::create(pExpCtx, pathString, preserveNullAndEmptyArrays, indexPath);
}
} // namespace mongo
|