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* Copyright (C) 2011 10gen Inc.
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* GNU Affero General Public License for more details.
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <>.
* 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 GNU Affero General 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/platform/basic.h"
#include "mongo/db/pipeline/document_source_limit.h"
#include "mongo/db/jsobj.h"
#include "mongo/db/pipeline/document.h"
#include "mongo/db/pipeline/expression.h"
#include "mongo/db/pipeline/expression_context.h"
#include "mongo/db/pipeline/lite_parsed_document_source.h"
#include "mongo/db/pipeline/value.h"
namespace mongo {
using boost::intrusive_ptr;
DocumentSourceLimit::DocumentSourceLimit(const intrusive_ptr<ExpressionContext>& pExpCtx,
long long limit)
: DocumentSource(pExpCtx), _limit(limit) {}
const char* DocumentSourceLimit::getSourceName() const {
return "$limit";
Pipeline::SourceContainer::iterator DocumentSourceLimit::doOptimizeAt(
Pipeline::SourceContainer::iterator itr, Pipeline::SourceContainer* container) {
invariant(*itr == this);
auto nextLimit = dynamic_cast<DocumentSourceLimit*>((*std::next(itr)).get());
if (nextLimit) {
_limit = std::min(_limit, nextLimit->getLimit());
return itr;
return std::next(itr);
DocumentSource::GetNextResult DocumentSourceLimit::getNext() {
if (_nReturned >= _limit) {
return GetNextResult::makeEOF();
auto nextInput = pSource->getNext();
if (nextInput.isAdvanced()) {
if (_nReturned >= _limit) {
return nextInput;
Value DocumentSourceLimit::serialize(boost::optional<ExplainOptions::Verbosity> explain) const {
return Value(Document{{getSourceName(), _limit}});
intrusive_ptr<DocumentSourceLimit> DocumentSourceLimit::create(
const intrusive_ptr<ExpressionContext>& pExpCtx, long long limit) {
uassert(15958, "the limit must be positive", limit > 0);
intrusive_ptr<DocumentSourceLimit> source(new DocumentSourceLimit(pExpCtx, limit));
return source;
intrusive_ptr<DocumentSource> DocumentSourceLimit::createFromBson(
BSONElement elem, const intrusive_ptr<ExpressionContext>& pExpCtx) {
uassert(15957, "the limit must be specified as a number", elem.isNumber());
long long limit = elem.numberLong();
return DocumentSourceLimit::create(pExpCtx, limit);