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/**
* Copyright (C) 2019-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/exec/document_value/document_metadata_fields.h"
#include "mongo/db/query/projection_ast.h"
#include "mongo/util/str.h"
namespace mongo {
namespace projection_ast {
/**
* Summary of the dependency analysis done on the projection AST.
*/
struct ProjectionDependencies {
// Whether MatchDetails of the query's filter are required.
bool requiresMatchDetails = false;
// Whether the entire document is required to do the projection.
bool requiresDocument = false;
bool hasExpressions = false;
bool containsElemMatch = false;
// If inclusion projection, contains field paths that are necessary to perform the projection,
// or boost::none if all are required. If exclusion projection, contains field paths that are
// explicitly excluded.
boost::optional<OrderedPathSet> paths;
bool hasDottedPath = false;
QueryMetadataBitSet metadataRequested;
};
/**
* Used to represent a projection for dependency analysis and query planning.
*/
enum class ProjectType { kInclusion, kExclusion };
class Projection {
public:
Projection(ProjectionPathASTNode root, ProjectType type);
ProjectionPathASTNode* root() {
return &_root;
}
const ProjectionPathASTNode* root() const {
return &_root;
}
ProjectType type() const {
return _type;
}
/**
* Returns true if the projection requires match details from the query,
* and false otherwise.
*/
bool requiresMatchDetails() const {
return _deps.requiresMatchDetails;
}
/**
* Returns whether the full document is required to compute this projection.
*/
bool requiresDocument() const {
return _deps.requiresDocument;
}
/**
* Return which fields are required to compute the projection, assuming the entire document is
* not needed. Includes _id explicitly if it is required - implicitily or explicitly.
*/
const OrderedPathSet& getRequiredFields() const {
invariant(_type == ProjectType::kInclusion);
return *_deps.paths;
}
const OrderedPathSet& getExcludedPaths() const {
invariant(_type == ProjectType::kExclusion);
return *_deps.paths;
}
const QueryMetadataBitSet& metadataDeps() const {
return _deps.metadataRequested;
}
/**
* Returns true if the element at 'path' is preserved entirely after this projection is applied,
* and false otherwise. For example, the projection {a: 1} will preserve the element located at
* 'a.b', and the projection {'a.b': 0} will not preserve the element located at 'a'.
*/
bool isFieldRetainedExactly(StringData path) const;
/**
* Returns true if this projection has any dotted paths; false otherwise.
*/
bool hasDottedPaths() const {
return _deps.hasDottedPath;
}
/**
* A projection is considered "simple" if it operates only on top-level fields,
* has no positional projection or expressions, and doesn't require metadata.
* Both exclusion and inclusion projections can be simple.
*/
bool isSimple() const {
return !_deps.hasDottedPath && !_deps.requiresMatchDetails &&
!_deps.metadataRequested.any() && !_deps.hasExpressions;
}
/**
* Returns true if this projection has any fields which are the result of computing an
* expression.
*/
bool hasExpressions() const {
return _deps.hasExpressions;
}
/**
* Check if this an inclusion only projection, without expressions and metadata, and the entire
* document is not required.
*/
bool isInclusionOnly() const {
return _type == ProjectType::kInclusion && !_deps.requiresMatchDetails &&
_deps.metadataRequested.none() && !_deps.requiresDocument && !_deps.hasExpressions;
}
/**
* Check if this an exclusion only projection, without expressions or metadata dependencies.
*/
bool isExclusionOnly() const {
return _type == ProjectType::kExclusion && !_deps.requiresMatchDetails &&
_deps.metadataRequested.none() && !_deps.hasExpressions;
}
bool containsElemMatch() const {
return _deps.containsElemMatch;
}
private:
ProjectionPathASTNode _root;
ProjectType _type;
ProjectionDependencies _deps;
};
/**
* Walks the projection AST and optimizes each node.
*/
void optimizeProjection(ProjectionPathASTNode* root);
} // namespace projection_ast
} // namespace mongo
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