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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 <boost/optional.hpp>
#include "mongo/db/pipeline/pipeline.h"
namespace mongo {
class SkipAndLimit {
public:
boost::optional<long long> getLimit() const;
boost::optional<long long> getSkip() const;
protected:
boost::optional<long long> _skip;
boost::optional<long long> _limit;
};
class SkipThenLimit;
class LimitThenSkip;
/**
* A struct representing a skip and a limit, with the skip to be applied before the limit.
*/
class SkipThenLimit final : public SkipAndLimit {
public:
SkipThenLimit(boost::optional<long long> skip, boost::optional<long long> limit);
};
/**
* A struct representing a limit and a skip, with the limit to be applied before the skip.
*/
class LimitThenSkip final : public SkipAndLimit {
public:
/**
* Initiates struct with given limit and skip sizes. If skip size is greater than limit size,
* it will take minimum of two values for skip size. This is done because we cannot skip more
* documents than limit returned.
*/
LimitThenSkip(boost::optional<long long> limit, boost::optional<long long> skip);
/**
* Returns SkipThenLimit structure representing logically the same operation, but by performing
* skip before the limit.
*/
SkipThenLimit flip() const;
};
/**
* If there are any $limit stages that could be logically swapped forward to the position of the
* pipeline pointed to by 'itr' without changing the meaning of the query, removes these $limit
* stages from the Pipeline and returns the resulting limit. A single limit value is computed by
* taking the minimum after swapping each individual $limit stage forward.
*
* This method also implements the ability to swap a $limit before a $skip, by adding the value of
* the $skip to the value of the $limit.
*/
boost::optional<long long> extractLimitForPushdown(Pipeline::SourceContainer::iterator itr,
Pipeline::SourceContainer* container);
/**
* This is similar to extractLimitForPushdown, except that it should be used when the caller does
* not want to modify the pipeline but still obtain the calculated limit value of the query.
*/
boost::optional<long long> getUserLimit(Pipeline::SourceContainer::iterator itr,
Pipeline::SourceContainer* container);
/**
* If there are any $skip stages that could be logically swapped forward to the position of the
* pipeline pointed to by 'itr' without changing the meaning of the query, removes these $skip
* stages from the Pipeline and returns the resulting skip. A single skip value is computed by
* taking the sum of all $skip stages that participate in swap.
*
* This method does NOT swap $skip before $limit. One can use 'extractLimitForPushdown' method to
* extract all $limit stages and then call this method if it is applicable.
*/
boost::optional<long long> extractSkipForPushdown(Pipeline::SourceContainer::iterator itr,
Pipeline::SourceContainer* container);
} // namespace mongo
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