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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/jsobj.h"
#include "mongo/db/pipeline/document.h"
#include "mongo/db/pipeline/document_source.h"
#include "mongo/db/pipeline/expression.h"
#include "mongo/db/pipeline/expression_context.h"
#include "mongo/db/pipeline/value.h"
namespace mongo {
using boost::intrusive_ptr;
DocumentSourceSkip::DocumentSourceSkip(const intrusive_ptr<ExpressionContext>& pExpCtx)
: DocumentSource(pExpCtx), _skip(0), _needToSkip(true) {}
REGISTER_DOCUMENT_SOURCE(skip, DocumentSourceSkip::createFromBson);
const char* DocumentSourceSkip::getSourceName() const {
return "$skip";
bool DocumentSourceSkip::coalesce(const intrusive_ptr<DocumentSource>& pNextSource) {
DocumentSourceSkip* pSkip = dynamic_cast<DocumentSourceSkip*>(pNextSource.get());
/* if it's not another $skip, we can't coalesce */
if (!pSkip)
return false;
/* we need to skip over the sum of the two consecutive $skips */
_skip += pSkip->_skip;
return true;
boost::optional<Document> DocumentSourceSkip::getNext() {
if (_needToSkip) {
_needToSkip = false;
for (long long i = 0; i < _skip; i++) {
if (!pSource->getNext())
return boost::none;
return pSource->getNext();
Value DocumentSourceSkip::serialize(bool explain) const {
return Value(DOC(getSourceName() << _skip));
intrusive_ptr<DocumentSource> DocumentSourceSkip::optimize() {
return _skip == 0 ? nullptr : this;
intrusive_ptr<DocumentSourceSkip> DocumentSourceSkip::create(
const intrusive_ptr<ExpressionContext>& pExpCtx) {
intrusive_ptr<DocumentSourceSkip> pSource(new DocumentSourceSkip(pExpCtx));
return pSource;
intrusive_ptr<DocumentSource> DocumentSourceSkip::createFromBson(
BSONElement elem, const intrusive_ptr<ExpressionContext>& pExpCtx) {
str::stream() << "Argument to $skip must be a number not a " << typeName(elem.type()),
intrusive_ptr<DocumentSourceSkip> pSkip(DocumentSourceSkip::create(pExpCtx));
pSkip->_skip = elem.numberLong();
uassert(15956, "Argument to $skip cannot be negative", pSkip->_skip >= 0);
return pSkip;
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