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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"
namespace mongo {
class DocumentSourceLimit final : public DocumentSource {
public:
static constexpr StringData kStageName = "$limit"_sd;
/**
* Create a new $limit stage.
*/
static boost::intrusive_ptr<DocumentSourceLimit> create(
const boost::intrusive_ptr<ExpressionContext>& pExpCtx, long long limit);
/**
* Parse a $limit stage from a BSON stage specification. 'elem's field name must be "$limit".
*/
static boost::intrusive_ptr<DocumentSource> createFromBson(
BSONElement elem, const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
StageConstraints constraints(Pipeline::SplitState pipeState) const final {
return {StreamType::kStreaming,
PositionRequirement::kNone,
HostTypeRequirement::kNone,
DiskUseRequirement::kNoDiskUse,
FacetRequirement::kAllowed,
TransactionRequirement::kAllowed,
LookupRequirement::kAllowed};
}
const char* getSourceName() const final {
return kStageName.rawData();
}
/**
* Attempts to combine with a subsequent $limit stage, setting 'limit' appropriately.
*/
Pipeline::SourceContainer::iterator doOptimizeAt(Pipeline::SourceContainer::iterator itr,
Pipeline::SourceContainer* container) final;
Value serialize(boost::optional<ExplainOptions::Verbosity> explain = boost::none) const final;
DepsTracker::State getDependencies(DepsTracker* deps) const final {
return DepsTracker::State::SEE_NEXT; // This doesn't affect needed fields
}
/**
* Returns a DistributedPlanLogic with two identical $limit stages; one for the shards pipeline
* and one for the merging pipeline.
*/
boost::optional<DistributedPlanLogic> distributedPlanLogic() final {
// Running this stage on the shards is an optimization, but is not strictly necessary in
// order to produce correct pipeline output.
// {shardsStage, mergingStage, sortPattern}
return DistributedPlanLogic{
this, DocumentSourceLimit::create(pExpCtx, _limit), boost::none};
}
long long getLimit() const {
return _limit;
}
void setLimit(long long newLimit) {
_limit = newLimit;
}
private:
DocumentSourceLimit(const boost::intrusive_ptr<ExpressionContext>& pExpCtx, long long limit);
GetNextResult doGetNext() final;
long long _limit;
long long _nReturned = 0;
};
} // namespace mongo
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