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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 <string>
#include "mongo/bson/bsonobjbuilder.h"
#include "mongo/db/exec/fastpath_projection_node.h"
#include "mongo/db/exec/projection_executor.h"
#include "mongo/db/exec/projection_node.h"
#include "mongo/db/pipeline/expression_dependencies.h"
namespace mongo::projection_executor {
/**
* A node used to define the parsed structure of an exclusion projection. Each ExclusionNode
* represents one 'level' of the parsed specification. The root ExclusionNode represents all top
* level exclusions, with any child ExclusionNodes representing dotted or nested exclusions.
*/
class ExclusionNode : public ProjectionNode {
public:
ExclusionNode(ProjectionPolicies policies, std::string pathToNode = "")
: ProjectionNode(policies, std::move(pathToNode)) {}
ExclusionNode* addOrGetChild(const std::string& field) {
return static_cast<ExclusionNode*>(ProjectionNode::addOrGetChild(field));
}
void reportDependencies(DepsTracker* deps) const final {
// We have no dependencies on specific fields, since we only know the fields to be removed.
// We may have expression dependencies though, as $meta expression can be used with
// exclusion.
for (auto&& expressionPair : _expressions) {
expression::addDependencies(expressionPair.second.get(), deps);
}
for (auto&& childPair : _children) {
childPair.second->reportDependencies(deps);
}
}
/**
* Removes and returns a BSONObj representing the part of this project that depends only on
* 'oldName'. Also returns a bool indicating whether this entire project is extracted. In the
* extracted $project, 'oldName' is renamed to 'newName'. 'oldName' should not be dotted.
*/
std::pair<BSONObj, bool> extractProjectOnFieldAndRename(const StringData& oldName,
const StringData& newName);
protected:
std::unique_ptr<ProjectionNode> makeChild(const std::string& fieldName) const {
return std::make_unique<ExclusionNode>(
_policies, FieldPath::getFullyQualifiedPath(_pathToNode, fieldName));
}
MutableDocument initializeOutputDocument(const Document& inputDoc) const final {
return MutableDocument{inputDoc};
}
Value applyLeafProjectionToValue(const Value& value) const final {
return Value();
}
Value transformSkippedValueForOutput(const Value& value) const final {
return value;
}
};
/**
* A fast-path exclusion projection implementation which applies a BSON-to-BSON transformation
* rather than constructing an output document using the Document/Value API. For exclusion-only
* projections (as defined by projection_ast::Projection::isExclusionOnly) it can be much faster
* than the default ExclusionNode implementation. On a document-by-document basis, if the fast-path
* projection cannot be applied to the input document, it will fall back to the default
* implementation.
*/
class FastPathEligibleExclusionNode final
: public FastPathProjectionNode<FastPathEligibleExclusionNode, ExclusionNode> {
private:
using Base = FastPathProjectionNode<FastPathEligibleExclusionNode, ExclusionNode>;
public:
using Base::Base;
Document applyToDocument(const Document& inputDoc) const final;
protected:
std::unique_ptr<ProjectionNode> makeChild(const std::string& fieldName) const final {
return std::make_unique<FastPathEligibleExclusionNode>(
_policies, FieldPath::getFullyQualifiedPath(_pathToNode, fieldName));
}
private:
void _applyToProjectedField(const BSONElement& element, BSONObjBuilder* bob) const {
// No-op -- this element is excluded.
}
void _applyToNonProjectedField(const BSONElement& element, BSONObjBuilder* bob) const {
// This element is not excluded by the projection, so it is added to the output.
bob->append(element);
}
void _applyToNonProjectedField(const BSONElement& element, BSONArrayBuilder* bab) const {
// This array element is not excluded by the projection, so it is added to the output.
bab->append(element);
}
void _applyToRemainingFields(BSONObjIterator& it, BSONObjBuilder* bob) const {
// We processed all exclusions, rest of the elements are added to the output.
while (it.more()) {
bob->append(it.next());
}
}
friend class FastPathProjectionNode<FastPathEligibleExclusionNode, ExclusionNode>;
};
/**
* A ExclusionProjectionExecutor represents an execution tree for an exclusion projection.
*
* This class is mostly a wrapper around an ExclusionNode tree and defers most execution logic to
* the underlying tree.
*/
class ExclusionProjectionExecutor : public ProjectionExecutor {
public:
ExclusionProjectionExecutor(
const boost::intrusive_ptr<ExpressionContext>& expCtx,
ProjectionPolicies policies,
bool allowFastPath = false,
boost::optional<projection_ast::ProjectionPathASTNode> proj = boost::none);
TransformerType getType() const final {
return TransformerType::kExclusionProjection;
}
const ExclusionNode* getRoot() const {
return _root.get();
}
ExclusionNode* getRoot() {
return _root.get();
}
Document serializeTransformation(boost::optional<ExplainOptions::Verbosity> explain,
SerializationOptions options = {}) const final {
MutableDocument output;
// The ExclusionNode tree in '_root' will always have a top-level _id node if _id is to be
// excluded. If the _id node is not present, then explicitly set {_id: true} to avoid
// ambiguity in the expected behavior of the serialized projection.
_root->serialize(explain, &output, options);
auto idFieldName = options.serializeFieldPath("_id");
if (output.peek()[idFieldName].missing()) {
output.addField(idFieldName, Value{true});
}
return output.freeze();
}
/**
* Exclude the fields specified.
*/
Document applyProjection(const Document& inputDoc) const final {
return _root->applyToDocument(inputDoc);
}
DepsTracker::State addDependencies(DepsTracker* deps) const final {
_root->reportDependencies(deps);
if (_rootReplacementExpression) {
expression::addDependencies(_rootReplacementExpression.get(), deps);
}
return DepsTracker::State::SEE_NEXT;
}
void addVariableRefs(std::set<Variables::Id>* refs) const final {
_root->addVariableRefs(refs);
if (_rootReplacementExpression) {
expression::addVariableRefs(_rootReplacementExpression.get(), refs);
}
}
DocumentSource::GetModPathsReturn getModifiedPaths() const final {
// A root-replacement expression can replace the entire root document, so all paths are
// considered as modified.
if (_rootReplacementExpression) {
return {DocumentSource::GetModPathsReturn::Type::kAllPaths, {}, {}};
}
OrderedPathSet modifiedPaths;
_root->reportProjectedPaths(&modifiedPaths);
return {DocumentSource::GetModPathsReturn::Type::kFiniteSet, std::move(modifiedPaths), {}};
}
boost::optional<std::set<FieldRef>> extractExhaustivePaths() const {
return boost::none;
}
std::pair<BSONObj, bool> extractProjectOnFieldAndRename(const StringData& oldName,
const StringData& newName) final {
return _root->extractProjectOnFieldAndRename(oldName, newName);
}
private:
// The ExclusionNode tree does most of the execution work once constructed.
std::unique_ptr<ExclusionNode> _root;
};
} // namespace mongo::projection_executor
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