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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 "mongo/platform/basic.h"
#include <boost/intrusive_ptr.hpp>
#include <memory>
#include "mongo/bson/bsonelement.h"
#include "mongo/db/pipeline/expression_context.h"
#include "mongo/db/pipeline/field_path.h"
#include "mongo/db/pipeline/transformer_interface.h"
#include "mongo/db/query/projection_policies.h"
namespace mongo::projection_executor {
/**
* A ProjectionExecutor is responsible for parsing and executing a $project. It represents either an
* inclusion or exclusion projection. This is the common interface between the two types of
* projections.
*/
class ProjectionExecutor : public TransformerInterface {
public:
/**
* The name of an internal variable to bind a projection post image to, which is used by the
* '_rootReplacementExpression' to replace the content of the transformed document.
*/
static constexpr StringData kProjectionPostImageVarName{"INTERNAL_PROJ_POST_IMAGE"_sd};
/**
* Optimize any expressions contained within this projection.
*/
void optimize() override {
if (_rootReplacementExpression) {
_rootReplacementExpression->optimize();
}
}
/**
* Add any dependencies needed by this projection or any sub-expressions to 'deps'.
*/
DepsTracker::State addDependencies(DepsTracker* deps) const override {
return DepsTracker::State::NOT_SUPPORTED;
}
/**
* Apply the projection transformation.
*/
Document applyTransformation(const Document& input) override {
auto output = applyProjection(input);
if (_rootReplacementExpression) {
return _applyRootReplacementExpression(input, output);
}
return output;
}
/**
* Sets 'expr' as a root-replacement expression to this tree. A root-replacement expression,
* once evaluated, will replace an entire output document. A projection post image document
* will be accessible via the special variable, whose name is stored in
* 'kProjectionPostImageVarName', if this expression needs access to it.
*/
void setRootReplacementExpression(boost::intrusive_ptr<Expression> expr) {
_rootReplacementExpression = expr;
}
/**
* Returns the root-replacement expression to this tree. Can return nullptr if this tree does
* not have a root replacing expression.
*/
boost::intrusive_ptr<Expression> rootReplacementExpression() const {
return _rootReplacementExpression;
}
/**
* Returns the exhaustive set of all paths that will be preserved by this projection, or
* boost::none if the exhaustive set cannot be determined.
*/
virtual boost::optional<std::set<FieldRef>> extractExhaustivePaths() const = 0;
/**
* The query shape is made by serializing the first parsed representation of the query, which in
* the case of $project queries is a projection_ast::Projection. The ProjectionExecutor, holds
* onto the root node of the AST for only $project queries, so that the first parsed
* representation is accessible at serialization.
*/
boost::optional<projection_ast::ProjectionPathASTNode> projection = boost::none;
protected:
ProjectionExecutor(const boost::intrusive_ptr<ExpressionContext>& expCtx,
ProjectionPolicies policies,
boost::optional<projection_ast::ProjectionPathASTNode> proj = boost::none)
: projection(proj),
_expCtx(expCtx),
_policies(policies),
_projectionPostImageVarId{
_expCtx->variablesParseState.defineVariable(kProjectionPostImageVarName)} {}
/**
* Apply the projection to 'input'.
*/
virtual Document applyProjection(const Document& input) const = 0;
boost::intrusive_ptr<ExpressionContext> _expCtx;
ProjectionPolicies _policies;
boost::intrusive_ptr<Expression> _rootReplacementExpression;
private:
Document _applyRootReplacementExpression(const Document& input, const Document& output) {
using namespace fmt::literals;
_expCtx->variables.setValue(_projectionPostImageVarId, Value{output});
auto val = _rootReplacementExpression->evaluate(input, &_expCtx->variables);
uassert(51254,
"Root-replacement expression must return a document, but got {}"_format(
typeName(val.getType())),
val.getType() == BSONType::Object);
return val.getDocument();
}
// This variable id is used to bind a projection post-image so that it can be accessed by
// root-replacement expressions which apply projection to the entire post-image document, rather
// than to a specific field.
Variables::Id _projectionPostImageVarId;
};
} // namespace mongo::projection_executor
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