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/**
* Copyright (C) 2021-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.
*/
#include "mongo/db/pipeline/expression.h"
#include "mongo/db/pipeline/memory_usage_tracker.h"
namespace mongo {
/**
* Performs comparisons across documents in an aggregation pipeline to determine when a new
* partition starts.
*/
class PartitionKeyComparator {
public:
PartitionKeyComparator(ExpressionContext* expCtx,
boost::intrusive_ptr<Expression> partitionExpr,
Document firstDoc)
: _expCtx(expCtx), _expr(std::move(partitionExpr)) {
tassert(5733800, "Null expression context passed to PartitionKeyComparator", _expCtx);
tassert(5733801, "Null expression passed to PartitionKeyComparator", _expr);
_partitionValue = evaluateAndCoerce(firstDoc);
}
/**
* Check to see if the passed in 'doc' begins a new partition.
*/
bool isDocumentNewPartition(Document doc) {
auto newVal = evaluateAndCoerce(doc);
// If one of the values are different, we are in a new partition.
if (_expCtx->getValueComparator().compare(newVal, _partitionValue) != 0) {
_partitionValue = std::move(newVal);
return true;
}
return false;
}
auto getApproximateSize() const {
return _partitionValue.getApproximateSize();
}
private:
Value evaluateAndCoerce(Document doc) {
// We assume that partitioning is acheived by sorting, and missing fields and nulls are
// considered equivalent in sorting. Documents with missing fields and nulls may
// interleave with each other, resulting in these documents processed into many separate
// partitions (null, missing, null, missing). However, it is still guranteed that all nulls
// and missing values will be grouped together after sorting. To address this issue, we
// coerce documents with the missing fields to null partition, which is also consistent with
// the approach in $group.
auto retValue = _expr->evaluate(doc, &_expCtx->variables);
uassert(ErrorCodes::TypeMismatch,
"An expression used to partition cannot evaluate to value of type array",
!retValue.isArray());
return retValue.missing() ? Value(BSONNULL) : std::move(retValue);
}
ExpressionContext* _expCtx;
boost::intrusive_ptr<Expression> _expr;
Value _partitionValue;
};
} // namespace mongo
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