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/**
* Copyright (C) 2019-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/exec/sbe/expressions/expression.h"
#include "mongo/db/exec/sbe/stages/stages.h"
#include "mongo/db/exec/sbe/vm/vm.h"
namespace mongo::sbe {
/**
* This is an array traversal operator. If the input value coming from the 'outer' side is an array
* then we execute the 'inner' side exactly once for every element of the array. The results from
* the 'inner' side are then collected into the output array value. The traversal is recursive and
* the structure of nested arrays is preserved (up to optional depth 'nestedArraysDepth'). If the
* input value is not an array then we execute the inner side just once and return the result.
*
* The 'inField' slot contains the value from the outer side which ie being traversed. When the
* traversal is complete, the resulting value is placed in the slot given by 'outField'. Note that
* it is legal for 'outField' and 'inField' to be the same slot when there are no fold or final
* expressions. The 'outFieldInner' slot is the slot that the traverse stage should read in order to
* get the resulting value whenever it executes the inner side. In other words, when the inner side
* is re-opened and executed once for a particular array element, the 'outFieldInner' slot holds the
* result of this operation (which may subsequently be passed to the fold/final expressions).
*
* The 'outerCorrelated' slots are slots from the outer side that are made visible to the inner
* side.
*
* If an optional 'foldExpr' expression is provided, then instead of the output array we combine
* individual results into a single output value. Another expression 'finalExpr' controls optional
* short-circuiting (a.k.a. early out) logic.
*
* Debug string representation:
*
* traverse outputSlot outputFromInnerBranchSlot inputSlot [<correlated slots>]
* { foldExpr }? { finalExpr }?
* from childStage
* in childStage
*/
class TraverseStage final : public PlanStage {
public:
TraverseStage(std::unique_ptr<PlanStage> outer,
std::unique_ptr<PlanStage> inner,
value::SlotId inField,
value::SlotId outField,
value::SlotId outFieldInner,
value::SlotVector outerCorrelated,
std::unique_ptr<EExpression> foldExpr,
std::unique_ptr<EExpression> finalExpr,
PlanNodeId planNodeId,
boost::optional<size_t> nestedArraysDepth,
bool participateInTrialRunTracking = true);
std::unique_ptr<PlanStage> clone() const final;
void prepare(CompileCtx& ctx) final;
value::SlotAccessor* getAccessor(CompileCtx& ctx, value::SlotId slot) final;
void open(bool reOpen) final;
PlanState getNext() final;
void close() final;
std::unique_ptr<PlanStageStats> getStats(bool includeDebugInfo) const final;
const SpecificStats* getSpecificStats() const final;
std::vector<DebugPrinter::Block> debugPrint() const final;
size_t estimateCompileTimeSize() const final;
protected:
void doSaveState(bool relinquishCursor) final;
void doRestoreState(bool relinquishCursor) final;
private:
void openInner(value::TypeTags tag, value::Value val);
bool traverse(value::SlotAccessor* inFieldAccessor,
value::OwnedValueAccessor* outFieldOutputAccessor,
size_t level);
PlanState getNextOuterSide() {
_isReadingLeftSide = true;
auto ret = _children[0]->getNext();
_isReadingLeftSide = false;
return ret;
}
// The input slot holding value being traversed.
const value::SlotId _inField;
// The output slot holding result of the traversal.
const value::SlotId _outField;
// The result of a single iteration of the traversal.
const value::SlotId _outFieldInner;
// Slots from the 'outer' side that are explicitly accessible on the 'inner' side.
const value::SlotVector _correlatedSlots;
// Optional folding expression for combining array elements.
const std::unique_ptr<EExpression> _fold;
// Optional boolean expression controlling short-circuiting of the fold.
const std::unique_ptr<EExpression> _final;
// Optional nested arrays recursion depth.
const boost::optional<size_t> _nestedArraysDepth;
value::SlotAccessor* _inFieldAccessor{nullptr};
value::ViewOfValueAccessor _correlatedAccessor;
value::OwnedValueAccessor _outFieldOutputAccessor;
value::SlotAccessor* _outFieldInputAccessor{nullptr};
std::unique_ptr<vm::CodeFragment> _foldCode;
std::unique_ptr<vm::CodeFragment> _finalCode;
std::list<value::ArrayAccessor> _inArrayAccessors;
vm::ByteCode _bytecode;
bool _compiled{false};
bool _reOpenInner{false};
TraverseStats _specificStats;
// Tracks whether or not we're reading from the left child or the right child.
// This is necessary for yielding.
bool _isReadingLeftSide = false;
};
} // namespace mongo::sbe
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