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/**
* Copyright (C) 2020-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_change_stream.h"
namespace mongo {
/**
* Part of the change stream API machinery used to look up the pre-image of a document.
*
* After a document that should have its pre-image included is transformed from the oplog,
* its "fullDocumentBeforeChange" field shall be the optime of the noop oplog entry containing the
* pre-image. This stage replaces that field with the actual pre-image document.
*/
class DocumentSourceLookupChangePreImage final : public DocumentSource {
public:
static constexpr StringData kStageName = "$_internalLookupChangePreImage"_sd;
static constexpr StringData kFullDocumentBeforeChangeFieldName =
DocumentSourceChangeStream::kFullDocumentBeforeChangeField;
/**
* Creates a DocumentSourceLookupChangePostImage stage.
*/
static boost::intrusive_ptr<DocumentSourceLookupChangePreImage> create(
const boost::intrusive_ptr<ExpressionContext>& expCtx,
const DocumentSourceChangeStreamSpec& spec);
DocumentSourceLookupChangePreImage(const boost::intrusive_ptr<ExpressionContext>& expCtx,
FullDocumentBeforeChangeModeEnum mode)
: DocumentSource(kStageName, expCtx), _fullDocumentBeforeChangeMode(mode) {
// This stage should never be created with FullDocumentBeforeChangeMode::kOff.
invariant(_fullDocumentBeforeChangeMode != FullDocumentBeforeChangeModeEnum::kOff);
}
/**
* Only modifies a single path: "fullDocumentBeforeChange".
*/
GetModPathsReturn getModifiedPaths() const final {
return {GetModPathsReturn::Type::kFiniteSet,
{kFullDocumentBeforeChangeFieldName.toString()},
{}};
}
StageConstraints constraints(Pipeline::SplitState pipeState) const final {
invariant(pipeState != Pipeline::SplitState::kSplitForShards);
StageConstraints constraints(StreamType::kStreaming,
PositionRequirement::kNone,
HostTypeRequirement::kAnyShard,
DiskUseRequirement::kNoDiskUse,
FacetRequirement::kNotAllowed,
TransactionRequirement::kNotAllowed,
LookupRequirement::kNotAllowed,
UnionRequirement::kNotAllowed,
ChangeStreamRequirement::kChangeStreamStage);
constraints.canSwapWithMatch = true;
return constraints;
}
// Conceptually, this stage must always run on the shards part of the pipeline. At
// present, however, pre-image retrieval is not supported in a sharded cluster, and
// so the distributed plan logic will not be used.
boost::optional<DistributedPlanLogic> distributedPlanLogic() final {
return DistributedPlanLogic{this, nullptr, boost::none};
}
DepsTracker::State getDependencies(DepsTracker* deps) const {
deps->fields.insert(DocumentSourceChangeStream::kFullDocumentBeforeChangeField.toString());
// This stage does not restrict the output fields to a finite set, and has no impact on
// whether metadata is available or needed.
return DepsTracker::State::SEE_NEXT;
}
Value serialize(boost::optional<ExplainOptions::Verbosity> explain = boost::none) const final {
return (explain ? Value{Document{{kStageName, Document()}}} : Value());
}
const char* getSourceName() const final {
return kStageName.rawData();
}
private:
/**
* Performs the lookup to retrieve the full pre-image document for applicable operations.
*/
GetNextResult doGetNext() final;
/**
* Looks up and returns a pre-image document at the specified opTime in the oplog. Returns
* boost::none if the mode is "kWhenAvailable" and no such oplog entry was found. Throws if the
* pre-image mode is "kRequired" and no entry was found. Invariants that if an oplog entry with
* the given opTime is found, it is a no-op entry with a valid non-empty pre-image document.
*/
boost::optional<Document> lookupPreImage(const Document& inputDoc,
const repl::OpTime& opTime) const;
// Determines whether pre-images are strictly required or may be included only when available.
FullDocumentBeforeChangeModeEnum _fullDocumentBeforeChangeMode =
FullDocumentBeforeChangeModeEnum::kOff;
};
} // namespace mongo
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