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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/db/pipeline/document_source.h"
#include "mongo/db/pipeline/document_source_unwind.h"
#include "mongo/db/pipeline/expression.h"
#include "mongo/db/pipeline/lookup_set_cache.h"
#include "mongo/db/pipeline/value_comparator.h"
namespace mongo {
class DocumentSourceGraphLookUp final : public DocumentSource {
public:
static std::unique_ptr<LiteParsedDocumentSourceForeignCollections> liteParse(
const AggregationRequest& request, const BSONElement& spec);
GetNextResult getNext() final;
const char* getSourceName() const final;
BSONObjSet getOutputSorts() final;
void serializeToArray(
std::vector<Value>& array,
boost::optional<ExplainOptions::Verbosity> explain = boost::none) const final;
/**
* Returns the 'as' path, and possibly the fields modified by an absorbed $unwind.
*/
GetModPathsReturn getModifiedPaths() const final;
StageConstraints constraints(Pipeline::SplitState pipeState) const final {
StageConstraints constraints(StreamType::kStreaming,
PositionRequirement::kNone,
HostTypeRequirement::kPrimaryShard,
DiskUseRequirement::kNoDiskUse,
FacetRequirement::kAllowed,
TransactionRequirement::kAllowed);
constraints.canSwapWithMatch = true;
return constraints;
}
DepsTracker::State getDependencies(DepsTracker* deps) const final {
_startWith->addDependencies(deps);
return DepsTracker::State::SEE_NEXT;
};
void addInvolvedCollections(std::vector<NamespaceString>* collections) const final {
collections->push_back(_from);
}
void detachFromOperationContext() final;
void reattachToOperationContext(OperationContext* opCtx) final;
static boost::intrusive_ptr<DocumentSourceGraphLookUp> create(
const boost::intrusive_ptr<ExpressionContext>& expCtx,
NamespaceString fromNs,
std::string asField,
std::string connectFromField,
std::string connectToField,
boost::intrusive_ptr<Expression> startWith,
boost::optional<BSONObj> additionalFilter,
boost::optional<FieldPath> depthField,
boost::optional<long long> maxDepth,
boost::optional<boost::intrusive_ptr<DocumentSourceUnwind>> unwindSrc);
static boost::intrusive_ptr<DocumentSource> createFromBson(
BSONElement elem, const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
protected:
void doDispose() final;
/**
* Attempts to combine with a subsequent $unwind stage, setting the internal '_unwind' field.
*/
Pipeline::SourceContainer::iterator doOptimizeAt(Pipeline::SourceContainer::iterator itr,
Pipeline::SourceContainer* container) final;
private:
DocumentSourceGraphLookUp(
const boost::intrusive_ptr<ExpressionContext>& expCtx,
NamespaceString from,
std::string as,
std::string connectFromField,
std::string connectToField,
boost::intrusive_ptr<Expression> startWith,
boost::optional<BSONObj> additionalFilter,
boost::optional<FieldPath> depthField,
boost::optional<long long> maxDepth,
boost::optional<boost::intrusive_ptr<DocumentSourceUnwind>> unwindSrc);
Value serialize(boost::optional<ExplainOptions::Verbosity> explain = boost::none) const final {
// Should not be called; use serializeToArray instead.
MONGO_UNREACHABLE;
}
/**
* Prepares the query to execute on the 'from' collection wrapped in a $match by using the
* contents of '_frontier'.
*
* Fills 'cached' with any values that were retrieved from the cache.
*
* Returns boost::none if no query is necessary, i.e., all values were retrieved from the cache.
* Otherwise, returns a query object.
*/
boost::optional<BSONObj> makeMatchStageFromFrontier(DocumentUnorderedSet* cached);
/**
* If we have internalized a $unwind, getNext() dispatches to this function.
*/
GetNextResult getNextUnwound();
/**
* Perform a breadth-first search of the 'from' collection. '_frontier' should already be
* populated with the values for the initial query. Populates '_discovered' with the result(s)
* of the query.
*/
void doBreadthFirstSearch();
/**
* Populates '_frontier' with the '_startWith' value(s) from '_input' and then performs a
* breadth-first search. Caller should check that _input is not boost::none.
*/
void performSearch();
/**
* Updates '_cache' with 'result' appropriately, given that 'result' was retrieved when querying
* for 'queried'.
*/
void addToCache(const Document& result, const ValueUnorderedSet& queried);
/**
* Assert that '_visited' and '_frontier' have not exceeded the maximum meory usage, and then
* evict from '_cache' until this source is using less than '_maxMemoryUsageBytes'.
*/
void checkMemoryUsage();
/**
* Process 'result', adding it to '_visited' with the given 'depth', and updating '_frontier'
* with the object's 'connectTo' values.
*
* Returns whether '_visited' was updated, and thus, whether the search should recurse.
*/
bool addToVisitedAndFrontier(Document result, long long depth);
// $graphLookup options.
NamespaceString _from;
FieldPath _as;
FieldPath _connectFromField;
FieldPath _connectToField;
boost::intrusive_ptr<Expression> _startWith;
boost::optional<BSONObj> _additionalFilter;
boost::optional<FieldPath> _depthField;
boost::optional<long long> _maxDepth;
// The ExpressionContext used when performing aggregation pipelines against the '_from'
// namespace.
boost::intrusive_ptr<ExpressionContext> _fromExpCtx;
// The aggregation pipeline to perform against the '_from' namespace.
std::vector<BSONObj> _fromPipeline;
size_t _maxMemoryUsageBytes = 100 * 1024 * 1024;
// Track memory usage to ensure we don't exceed '_maxMemoryUsageBytes'.
size_t _visitedUsageBytes = 0;
size_t _frontierUsageBytes = 0;
// Only used during the breadth-first search, tracks the set of values on the current frontier.
ValueUnorderedSet _frontier;
// Tracks nodes that have been discovered for a given input. Keys are the '_id' value of the
// document from the foreign collection, value is the document itself. The keys are compared
// using the simple collation.
ValueUnorderedMap<Document> _visited;
// Caches query results to avoid repeating any work. This structure is maintained across calls
// to getNext().
LookupSetCache _cache;
// When we have internalized a $unwind, we must keep track of the input document, since we will
// need it for multiple "getNext()" calls.
boost::optional<Document> _input;
// Keep track of a $unwind that was absorbed into this stage.
boost::optional<boost::intrusive_ptr<DocumentSourceUnwind>> _unwind;
// If we absorbed a $unwind that specified 'includeArrayIndex', this is used to populate that
// field, tracking how many results we've returned so far for the current input document.
long long _outputIndex;
};
} // namespace mongo
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