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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 <boost/intrusive_ptr.hpp>
#include "mongo/bson/bsonelement.h"
#include "mongo/db/pipeline/accumulator.h"
#include "mongo/db/pipeline/expression.h"
namespace mongo {
/**
* Registers an Accumulator to have the name 'key'. When an accumulator with name '$key' is found
* during parsing, 'factory' will be called to construct the Accumulator.
*
* As an example, if your accumulator looks like {"$foo": <args>}, with a factory method 'create',
* you would add this line:
* REGISTER_ACCUMULATOR(foo, AccumulatorFoo::create);
*/
#define REGISTER_ACCUMULATOR(key, factory) \
MONGO_INITIALIZER(addToAccumulatorFactoryMap_##key)(InitializerContext*) { \
AccumulationStatement::registerAccumulator("$" #key, (factory)); \
return Status::OK(); \
}
/**
* A class representing a user-specified accummulation, including the field name to put the
* accumulated result in, which accumulator to use, and the expression used to obtain the input to
* the Accumulator.
*/
class AccumulationStatement {
public:
AccumulationStatement(std::string fieldName,
boost::intrusive_ptr<Expression> expression,
Accumulator::Factory factory)
: fieldName(std::move(fieldName)),
expression(std::move(expression)),
_factory(std::move(factory)) {}
/**
* Parses a BSONElement that is an accumulated field, and returns an AccumulationStatement for
* that accumulated field.
*
* Throws a AssertionException if parsing fails.
*/
static AccumulationStatement parseAccumulationStatement(
const boost::intrusive_ptr<ExpressionContext>& expCtx,
const BSONElement& elem,
const VariablesParseState& vps);
/**
* Registers an Accumulator with a parsing function, so that when an accumulator with the given
* name is encountered during parsing, we will know to call 'factory' to construct that
* Accumulator.
*
* DO NOT call this method directly. Instead, use the REGISTER_ACCUMULATOR macro defined in this
* file.
*/
static void registerAccumulator(std::string name, Accumulator::Factory factory);
/**
* Retrieves the Factory for the accumulator specified by the given name, and raises an error if
* there is no such Accumulator registered.
*/
static Accumulator::Factory getFactory(StringData name);
// The field name is used to store the results of the accumulation in a result document.
std::string fieldName;
// The expression to use to obtain the input to the accumulator.
boost::intrusive_ptr<Expression> expression;
// Constructs an Accumulator to do actual accumulation.
boost::intrusive_ptr<Accumulator> makeAccumulator(
const boost::intrusive_ptr<ExpressionContext>& expCtx) const;
private:
Accumulator::Factory _factory;
};
} // namespace mongo
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