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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 <algorithm>
#include <boost/optional.hpp>
#include <deque>
#include <functional>
#include <memory>
#include <type_traits>
#include <utility>
#include <vector>
#include "mongo/db/pipeline/document_source.h"
#include "mongo/db/pipeline/document_source_facet.h"
#include "mongo/db/pipeline/document_source_lookup.h"
#include "mongo/db/pipeline/pipeline.h"
/**
* A simple representation of an Aggregation Pipeline and functions for building it.
* PipelineMetadataTree has no default contents and reflects only the shape of stages. Each stage
* can be occupied by a a specified type in order to have the tree carry any form of arbitrary
* metadata. A PipelineMetadataTree is intended to be zipped along with another representation of a
* pipeline in order to supplement the other representation's metadata.
*/
namespace mongo::pipeline_metadata_tree {
/**
* An alternate representation of a stage in an Aggregation Pipeline which contains handles to all
* stages it depends on, forming a tree. Each Stage tracks a specific piece of metadata of type 'T'.
* Since Stage forms a tree rather than a DAG, there are no handles from $facet component pipelines
* to their owning $facet stage but there exist pointers from any $facet stage to its component
* pipelines.
*/
template <typename T>
struct Stage {
/**
* Construct an individual Stage from its components.
*/
Stage(T&& contents,
std::unique_ptr<Stage> principalChild,
std::vector<Stage>&& additionalChildren)
: contents(std::move(contents)),
principalChild(std::move(principalChild)),
additionalChildren(std::move(additionalChildren)) {}
/**
* Specification of the move constructor intentionally inhibits compiler generation of a copy
* constructor. This is intentional since accidental copies could be deterimental for
* performance. This constructor is correctly formed only if the contents type 'T' also has a
* defined or defaulted move constructor. The correct definition of this constructor is
* essential for invoking 'makeTree'.
*/
Stage(Stage&&) = default;
/**
* The move assignment operator is subject to the same conditions as the move constructor.
*/
Stage& operator=(Stage&&) = default;
/**
* A comparison operator is correctly defined if the type 'T' has a defined comparison operator.
* This is optional.
*/
bool operator==(const Stage& other) const {
return contents == other.contents &&
(principalChild && other.principalChild ? *principalChild == *other.principalChild
: !principalChild && !other.principalChild) &&
additionalChildren == other.additionalChildren;
}
T contents;
/**
* The child occuring directly before this stage in the pipeline. This is empty for the first
* Stage in any pipeline or sub-pipeline.
*/
std::unique_ptr<Stage> principalChild;
/**
* Additional children are the ends of sub-pipelines that feed into this stage. This vector is
* non-empty only for stages which operate on one or more sub-pipelines such as $facet.
*/
std::vector<Stage> additionalChildren;
};
/**
* Following convention, the nested detail namespace should be treated as private and not accessed
* directly.
*/
namespace detail {
template <typename T>
std::pair<boost::optional<Stage<T>>, std::function<T(const T&)>> makeTreeWithOffTheEndStage(
std::deque<T>&& initialStageContents,
const Pipeline& pipeline,
const std::function<T(const T&, const std::vector<T>&, const DocumentSource&)>& propagator);
/**
* Produces additional children to be included in a given Stage if it has sub-pipelines. Included
* are off-the-end contents that would be generated for those sub-pipelines if they had one
* additional Stage. A deque 'initialStageContents' is provided to dequeue from in order to populate
* sub-pipelines that, in a graph model, never source from the current pipeline but only feed into
* it. For example, the initial stage contents are used to seed the contents of $lookup
* sub-pipelines. The current Stage's contents are provided to copy and populate sub-pipelines that
* source from the current pipeline and feed back into it through a successive edge. For example,
* $facet sub-pipelines are populated using a copy of the current Stage's contents.
*/
template <typename T>
inline auto makeAdditionalChildren(
std::deque<T>&& initialStageContents,
const DocumentSource& source,
const std::function<T(const T&, const std::vector<T>&, const DocumentSource&)>& propagator,
const T& currentContentsToCopyForFacet) {
std::vector<Stage<T>> children;
std::vector<T> offTheEndContents;
if (auto lookupSource = dynamic_cast<const DocumentSourceLookUp*>(&source);
lookupSource && lookupSource->wasConstructedWithPipelineSyntax()) {
auto[child, offTheEndReshaper] =
makeTreeWithOffTheEndStage(std::move(initialStageContents),
lookupSource->getResolvedIntrospectionPipeline(),
propagator);
offTheEndContents.push_back(offTheEndReshaper(child.get().contents));
children.push_back(std::move(*child));
}
if (auto facetSource = dynamic_cast<const DocumentSourceFacet*>(&source))
std::transform(facetSource->getFacetPipelines().begin(),
facetSource->getFacetPipelines().end(),
std::back_inserter(children),
[&](const auto& fPipe) {
initialStageContents.push_front(currentContentsToCopyForFacet);
auto[child, offTheEndReshaper] = makeTreeWithOffTheEndStage(
std::move(initialStageContents), *fPipe.pipeline, propagator);
offTheEndContents.push_back(offTheEndReshaper(child.get().contents));
return std::move(*child);
});
return std::pair(std::move(children), std::move(offTheEndContents));
}
/**
* Produces a stage and returns a function to determine the contents for the next Stage. Given are
* an optional reference to a previous stage which is disengaged at the start of a pipeline or sub-
* pipeline. Also given is 'reshapeContents', a function to produce the content of the current
* stage. The current DocumentSource to build a corresponding Stage for is given through 'source'.
* The front of the 'initialStageContents' deque is used to populate the new Stage if there is no
* previous Stage and is ignored otherwise.
*/
template <typename T>
inline auto makeStage(
std::deque<T>&& initialStageContents,
boost::optional<Stage<T>>&& previous,
const std::function<T(const T&)>& reshapeContents,
const DocumentSource& source,
const std::function<T(const T&, const std::vector<T>&, const DocumentSource&)>& propagator) {
auto contents =
previous ? reshapeContents(previous.get().contents) : initialStageContents.front();
if (!previous)
initialStageContents.pop_front();
auto[additionalChildren, offTheEndContents] =
makeAdditionalChildren(std::move(initialStageContents), source, propagator, contents);
auto principalChild = previous ? std::make_unique<Stage<T>>(std::move(previous.get()))
: std::unique_ptr<Stage<T>>();
std::function<T(const T&)> reshaper([&, offTheEndContents{std::move(offTheEndContents)} ](
const T& reshapable) { return propagator(reshapable, offTheEndContents, source); });
return std::pair(
boost::optional<Stage<T>>(
Stage(std::move(contents), std::move(principalChild), std::move(additionalChildren))),
std::move(reshaper));
}
template <typename T>
inline std::pair<boost::optional<Stage<T>>, std::function<T(const T&)>> makeTreeWithOffTheEndStage(
std::deque<T>&& initialStageContents,
const Pipeline& pipeline,
const std::function<T(const T&, const std::vector<T>&, const DocumentSource&)>& propagator) {
std::pair<boost::optional<Stage<T>>, std::function<T(const T&)>> stageAndReshapeContents;
for (const auto& source : pipeline.getSources())
stageAndReshapeContents = makeStage(std::move(initialStageContents),
std::move(stageAndReshapeContents.first),
stageAndReshapeContents.second,
*source,
propagator);
return std::move(stageAndReshapeContents);
}
template <typename T>
inline void walk(Stage<T>* stage,
Pipeline::SourceContainer::iterator* sourceIter,
const std::function<void(Stage<T>*, DocumentSource*)>& zipper) {
if (stage->principalChild)
walk(stage->principalChild.get(), sourceIter, zipper);
if (auto lookupSource = dynamic_cast<DocumentSourceLookUp*>(&***sourceIter);
lookupSource && lookupSource->wasConstructedWithPipelineSyntax()) {
auto iter = lookupSource->getResolvedIntrospectionPipeline().getSources().begin();
walk(&stage->additionalChildren.front(), &iter, zipper);
}
if (auto facetSource = dynamic_cast<const DocumentSourceFacet*>(&***sourceIter)) {
auto facetIter = facetSource->getFacetPipelines().begin();
for (auto& child : stage->additionalChildren) {
auto iter = facetIter++->pipeline->getSources().begin();
walk(&child, &iter, zipper);
}
}
zipper(stage, &**(*sourceIter)++);
}
} // namespace detail
/**
* Builds a Stage from a Pipeline. Initial contents for the first pipline stage must be provided. A
* function 'propagator' is neccesary to determine how to build the contents of all further stages.
* A stage will receive the built contents from its directly preceding stage. Initial contents must
* be placed in 'initialStageContents'. Any expressive lookup pipelines require an additional
* initial content element in this queue.
*
* The arguments to propagator will be actualized with the following:
* 'T&' - In general, the contents from the previous stage, initial stages of the main pipeline and
* $lookup pipelines recieve an element off the queue 'initialStageContents'. $facet receives a copy
* of its parent's contents.
* 'std::vector<T>&' - Completed contents from sub-pipelines. $facet's additional children and
* expressive $lookup's final contents will be manifested in here. Note that these will be
* "off-the-end", that is constructed from the final stage of a sub-pipeline and not actually
* contained in that pipeline. This vector is empty for most stages which have only one child.
* 'DocumentSource&' - the current stage of the 'pipeline' a Stage object is being built for.
*/
template <typename T>
inline Stage<T> makeTree(
std::deque<T>&& initialStageContents,
const Pipeline& pipeline,
const std::function<T(const T&, const std::vector<T>&, const DocumentSource&)>& propagator) {
return *detail::makeTreeWithOffTheEndStage(
std::move(initialStageContents), pipeline, propagator)
.first;
}
/**
* Walk a PipelineMetadataTree along with a Pipeline. Passes each Stage and its corresponding
* DocumentSource to 'zipper' two-by-two.
*/
template <typename T>
inline void zip(Stage<T>* tree,
Pipeline* pipeline,
const std::function<void(Stage<T>*, DocumentSource*)>& zipper) {
auto iter = pipeline->getSources().begin();
detail::walk(tree, &iter, zipper);
}
} // namespace mongo::AggregatePipelineSchemaTracker
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