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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.
*/
#pragma once
#include "mongo/db/pipeline/document_source.h"
#include "mongo/db/pipeline/document_source_limit.h"
#include "mongo/db/pipeline/document_source_sort.h"
#include "mongo/db/pipeline/field_path.h"
namespace mongo {
class DocumentSourceUnwind final : public DocumentSource {
public:
static constexpr StringData kStageName = "$unwind"_sd;
// virtuals from DocumentSource
const char* getSourceName() const final;
Value serialize(boost::optional<ExplainOptions::Verbosity> explain = boost::none) const final;
/**
* Returns the unwound path, and the 'includeArrayIndex' path, if specified.
*/
GetModPathsReturn getModifiedPaths() const final;
StageConstraints constraints(Pipeline::SplitState pipeState) const final {
StageConstraints constraints(StreamType::kStreaming,
PositionRequirement::kNone,
HostTypeRequirement::kNone,
DiskUseRequirement::kNoDiskUse,
FacetRequirement::kAllowed,
TransactionRequirement::kAllowed,
LookupRequirement::kAllowed,
UnionRequirement::kAllowed);
constraints.canSwapWithMatch = true;
return constraints;
}
boost::optional<DistributedPlanLogic> distributedPlanLogic() final {
return boost::none;
}
DepsTracker::State getDependencies(DepsTracker* deps) const final;
/**
* Creates a new $unwind DocumentSource from a BSON specification.
*/
static boost::intrusive_ptr<DocumentSource> createFromBson(
BSONElement elem, const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
static boost::intrusive_ptr<DocumentSourceUnwind> create(
const boost::intrusive_ptr<ExpressionContext>& expCtx,
const std::string& path,
bool includeNullIfEmptyOrMissing,
const boost::optional<std::string>& includeArrayIndex,
bool strict = false);
std::string getUnwindPath() const {
return _unwindPath.fullPath();
}
bool preserveNullAndEmptyArrays() const {
return _preserveNullAndEmptyArrays;
}
const boost::optional<FieldPath>& indexPath() const {
return _indexPath;
}
protected:
/**
* Attempts to swap with a subsequent $sort stage if the $sort is on a different field.
*/
Pipeline::SourceContainer::iterator doOptimizeAt(Pipeline::SourceContainer::iterator itr,
Pipeline::SourceContainer* container) final;
private:
DocumentSourceUnwind(const boost::intrusive_ptr<ExpressionContext>& pExpCtx,
const FieldPath& fieldPath,
bool includeNullIfEmptyOrMissing,
const boost::optional<FieldPath>& includeArrayIndex,
bool strict);
GetNextResult doGetNext() final;
// Checks if a sort is eligible to be moved before the unwind.
bool canPushSortBack(const DocumentSourceSort* sort) const;
// Checks if a limit is eligible to be moved before the unwind.
bool canPushLimitBack(const DocumentSourceLimit* limit) const;
// Configuration state.
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;
// Iteration state.
class Unwinder;
std::unique_ptr<Unwinder> _unwinder;
// If preserveNullAndEmptyArrays is true and unwind is followed by a limit, we can duplicate
// the limit before the unwind. We only want to do this if we've found a limit smaller than the
// one we already pushed down. boost::none means no push down has occurred yet.
boost::optional<long long> _smallestLimitPushedDown;
};
} // namespace mongo
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