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/**
* Copyright (C) 2022-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/pipeline/expression.h"
#include "mongo/db/pipeline/transformer_interface.h"
namespace mongo {
/**
* GroupFromFirstTransformation consists of a list of (field name, expression pairs). It returns a
* document synthesized by assigning each field name in the output document to the result of
* evaluating the corresponding expression. If the expression evaluates to missing, we assign a
* value of BSONNULL. This is necessary to match the semantics of $first for missing fields.
*/
class GroupFromFirstDocumentTransformation final : public TransformerInterface {
public:
enum class ExpectedInput { kFirstDocument, kLastDocument };
GroupFromFirstDocumentTransformation(
const std::string& groupId,
StringData originalStageName,
std::vector<std::pair<std::string, boost::intrusive_ptr<Expression>>> accumulatorExprs,
ExpectedInput expectedInput = ExpectedInput::kFirstDocument)
: _accumulatorExprs(std::move(accumulatorExprs)),
_groupId(groupId),
_originalStageName(originalStageName),
_expectedInput(expectedInput) {}
TransformerType getType() const final {
return TransformerType::kGroupFromFirstDocument;
}
/**
* The path of the field that we are grouping on: i.e., the field in the input document that we
* will use to create the _id field of the ouptut document.
*/
const std::string& groupId() const {
return _groupId;
}
StringData originalStageName() const {
return _originalStageName;
}
ExpectedInput expectedInput() const {
return _expectedInput;
}
Document applyTransformation(const Document& input) final;
void optimize() final;
Document serializeTransformation(boost::optional<ExplainOptions::Verbosity> explain,
SerializationOptions options = {}) const final;
DepsTracker::State addDependencies(DepsTracker* deps) const final;
void addVariableRefs(std::set<Variables::Id>* refs) const final;
DocumentSource::GetModPathsReturn getModifiedPaths() const final;
static std::unique_ptr<GroupFromFirstDocumentTransformation> create(
const boost::intrusive_ptr<ExpressionContext>& expCtx,
const std::string& groupId,
StringData originalStageName,
std::vector<std::pair<std::string, boost::intrusive_ptr<Expression>>> accumulatorExprs,
ExpectedInput expectedInput);
private:
std::vector<std::pair<std::string, boost::intrusive_ptr<Expression>>> _accumulatorExprs;
std::string _groupId;
StringData _originalStageName;
ExpectedInput _expectedInput;
};
} // namespace mongo
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