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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/pipeline/document_source_merge_gen.h"
#include "mongo/db/pipeline/document_source_writer.h"
#include "mongo/db/pipeline/lite_parsed_pipeline.h"
namespace mongo {
/**
* A class for the $merge aggregation stage to handle all supported merge modes. Each instance of
* this class must be initialized (via a constructor) with a 'MergeDescriptor', which defines a
* a particular merge strategy for a pair of 'whenMatched' and 'whenNotMatched' merge modes.
*/
class DocumentSourceMerge final : public DocumentSourceWriter<MongoProcessInterface::BatchObject> {
public:
static constexpr StringData kStageName = "$merge"_sd;
// A descriptor for a merge strategy. Holds a merge strategy function and a set of actions
// the client should be authorized to perform in order to be able to execute a merge operation
// using this merge strategy.
struct MergeStrategyDescriptor {
using WhenMatched = MergeWhenMatchedModeEnum;
using WhenNotMatched = MergeWhenNotMatchedModeEnum;
using MergeMode = std::pair<WhenMatched, WhenNotMatched>;
// A function encapsulating a merge strategy for the $merge stage based on the pair of
// whenMatched/whenNotMatched modes.
using MergeStrategy = std::function<void(const boost::intrusive_ptr<ExpressionContext>&,
const NamespaceString&,
const WriteConcernOptions&,
boost::optional<OID>,
BatchedObjects&&)>;
MergeMode mode;
ActionSet actions;
MergeStrategy strategy;
};
/**
* A "lite parsed" $merge stage to disallow passthrough from mongos even if the source
* collection is unsharded. This ensures that the unique index verification happens once on
* mongos and can be bypassed on the shards.
*/
class LiteParsed final : public LiteParsedDocumentSourceNestedPipelines {
public:
LiteParsed(std::string parseTimeName,
NamespaceString foreignNss,
MergeWhenMatchedModeEnum whenMatched,
MergeWhenNotMatchedModeEnum whenNotMatched,
boost::optional<LiteParsedPipeline> onMatchedPipeline)
: LiteParsedDocumentSourceNestedPipelines(
std::move(parseTimeName), std::move(foreignNss), std::move(onMatchedPipeline)),
_whenMatched(whenMatched),
_whenNotMatched(whenNotMatched) {}
static std::unique_ptr<LiteParsed> parse(const NamespaceString& nss,
const BSONElement& spec);
bool allowedToPassthroughFromMongos() const {
return false;
}
ReadConcernSupportResult supportsReadConcern(repl::ReadConcernLevel level) const final {
return {
{level == repl::ReadConcernLevel::kLinearizableReadConcern,
{ErrorCodes::InvalidOptions,
"{} cannot be used with a 'linearizable' read concern level"_format(kStageName)}},
Status::OK()};
}
PrivilegeVector requiredPrivileges(bool isMongos,
bool bypassDocumentValidation) const final;
private:
MergeWhenMatchedModeEnum _whenMatched;
MergeWhenNotMatchedModeEnum _whenNotMatched;
};
virtual ~DocumentSourceMerge() = default;
const char* getSourceName() const final {
return kStageName.rawData();
}
StageConstraints constraints(Pipeline::SplitState pipeState) const final;
boost::optional<DistributedPlanLogic> distributedPlanLogic() final;
Value serialize(boost::optional<ExplainOptions::Verbosity> explain = boost::none) const final;
/**
* Creates a new $merge stage from the given arguments.
*/
static boost::intrusive_ptr<DocumentSource> create(
NamespaceString outputNs,
const boost::intrusive_ptr<ExpressionContext>& expCtx,
MergeStrategyDescriptor::WhenMatched whenMatched,
MergeStrategyDescriptor::WhenNotMatched whenNotMatched,
boost::optional<BSONObj> letVariables,
boost::optional<std::vector<BSONObj>> pipeline,
std::set<FieldPath> mergeOnFields,
boost::optional<ChunkVersion> targetCollectionVersion);
/**
* Parses a $merge stage from the user-supplied BSON.
*/
static boost::intrusive_ptr<DocumentSource> createFromBson(
BSONElement elem, const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
auto getPipeline() const {
return _pipeline;
}
private:
/**
* Builds a new $merge stage which will merge all documents into 'outputNs'. If
* 'targetCollectionVersion' is provided then processing will stop with an error if the
* collection's epoch changes during the course of execution. This is used as a mechanism to
* prevent the shard key from changing.
*/
DocumentSourceMerge(NamespaceString outputNs,
const boost::intrusive_ptr<ExpressionContext>& expCtx,
const MergeStrategyDescriptor& descriptor,
boost::optional<BSONObj> letVariables,
boost::optional<std::vector<BSONObj>> pipeline,
std::set<FieldPath> mergeOnFields,
boost::optional<ChunkVersion> targetCollectionVersion);
/**
* Creates an UpdateModification object from the given 'doc' to be used with the batched update.
*/
auto makeBatchUpdateModification(const Document& doc) const {
return _pipeline ? write_ops::UpdateModification(*_pipeline)
: write_ops::UpdateModification(doc.toBson());
}
/**
* Resolves 'let' defined variables against the 'doc' and stores the results in the returned
* BSON.
*/
boost::optional<BSONObj> resolveLetVariablesIfNeeded(const Document& doc) const {
// When we resolve 'let' variables, an empty BSON object or boost::none won't make any
// difference at the end-point (in the PipelineExecutor), as in both cases we will end up
// with the update pipeline ExpressionContext not being populated with any variables, so we
// are not making a distinction between these two cases here.
if (!_letVariables || _letVariables->empty()) {
return boost::none;
}
BSONObjBuilder bob;
for (auto&& [name, expr] : *_letVariables) {
bob << name << expr->evaluate(doc, &pExpCtx->variables);
}
return bob.obj();
}
void spill(BatchedObjects&& batch) override;
void waitWhileFailPointEnabled() override;
std::pair<BatchObject, int> makeBatchObject(Document&& doc) const override;
boost::optional<ChunkVersion> _targetCollectionVersion;
// A merge descriptor contains a merge strategy function describing how to merge two
// collections, as well as some other metadata needed to perform the merge operation. This is
// a reference to an element in a static const map 'kMergeStrategyDescriptors', which owns the
// descriptor.
const MergeStrategyDescriptor& _descriptor;
// Holds 'let' variables defined in this stage. These variables are propagated to the
// ExpressionContext of the pipeline update for use in the inner pipeline execution. The key
// of the map is a variable name as defined in the $merge spec 'let' argument, and the value is
// a parsed Expression, defining how the variable value must be evaluated.
boost::optional<stdx::unordered_map<std::string, boost::intrusive_ptr<Expression>>>
_letVariables;
// A custom pipeline to compute a new version of merging documents.
boost::optional<std::vector<BSONObj>> _pipeline;
// Holds the fields used for uniquely identifying documents. There must exist a unique index
// with this key pattern. Default is "_id" for unsharded collections, and "_id" plus the shard
// key for sharded collections.
std::set<FieldPath> _mergeOnFields;
// True if '_mergeOnFields' contains the _id. We store this as a separate boolean to avoid
// repeated lookups into the set.
bool _mergeOnFieldsIncludesId;
};
} // namespace mongo
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