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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 <memory>
#include "mongo/bson/bsonobj.h"
#include "mongo/db/field_ref.h"
namespace mongo {
/**
* This class provides the query system with the ability to perform projections using the
* aggregation system's projection semantics.
*/
class ProjectionExecAgg {
public:
// Allows the caller to indicate whether the projection should default to including or excluding
// the _id field in the event that the projection spec does not specify the desired behavior.
// For instance, given a projection {a: 1}, specifying 'kExcludeId' is equivalent to projecting
// {a: 1, _id: 0} while 'kIncludeId' is equivalent to the projection {a: 1, _id: 1}. If the user
// explicitly specifies a projection on _id, then this will override the default policy; for
// instance, {a: 1, _id: 0} will exclude _id for both 'kExcludeId' and 'kIncludeId'.
enum class DefaultIdPolicy { kIncludeId, kExcludeId };
// Allows the caller to specify how the projection should handle nested arrays; that is, an
// array whose immediate parent is itself an array. For example, in the case of sample document
// {a: [1, 2, [3, 4], {b: [5, 6]}]} the array [3, 4] is a nested array. The array [5, 6] is not,
// because there is an intervening object between it and its closest array ancestor.
enum class ArrayRecursionPolicy { kRecurseNestedArrays, kDoNotRecurseNestedArrays };
enum class ProjectionType { kInclusionProjection, kExclusionProjection };
static std::unique_ptr<ProjectionExecAgg> create(BSONObj projSpec,
DefaultIdPolicy defaultIdPolicy,
ArrayRecursionPolicy recursionPolicy);
~ProjectionExecAgg();
BSONObj applyProjection(BSONObj inputDoc) const;
stdx::unordered_set<std::string> applyProjectionToFields(
const stdx::unordered_set<std::string>& fields) const;
/**
* Apply the projection to a single field name. Returns whether or not the projection would
* allow that field to remain in a document.
**/
bool applyProjectionToOneField(StringData field) const;
/**
* Returns the exhaustive set of all paths that will be preserved by this projection, or an
* empty set if the exhaustive set cannot be determined. An inclusion will always produce an
* exhaustive set; an exclusion will always produce an empty set.
*/
const std::set<FieldRef>& getExhaustivePaths() const;
ProjectionType getType() const;
BSONObj getProjectionSpec() const {
return _projSpec;
}
private:
/**
* ProjectionExecAgg::ProjectionExecutor wraps all agg-specific calls, and is forward-declared
* here to avoid exposing any types from ParsedAggregationProjection to the query system.
*/
class ProjectionExecutor;
ProjectionExecAgg(BSONObj projSpec, std::unique_ptr<ProjectionExecutor> exec);
std::unique_ptr<ProjectionExecutor> _exec;
const BSONObj _projSpec;
};
} // namespace mongo
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