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/**
* Copyright (C) 2016 MongoDB Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* 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
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* 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 GNU Affero General 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 <vector>
#include "mongo/base/status.h"
#include "mongo/db/namespace_string.h"
#include "mongo/stdx/unordered_map.h"
#include "mongo/stdx/unordered_set.h"
#include "mongo/util/string_map.h"
namespace mongo {
class ViewDefinition;
/**
* Validates that the graph of view dependencies is acyclic and within the allowed depth.
* Each node is represented by an integer id, and stores integer ids for its parents and children
* in the graph.
*
* This is owned and managed by the ViewCatalog.
*/
class ViewGraph {
MONGO_DISALLOW_COPYING(ViewGraph);
public:
static const int kMaxViewDepth;
ViewGraph() = default;
/**
* Called when a view is added to the catalog. 'refs' are a list of namespaces that the view
* represented by 'viewNss' references in its viewOn or pipeline. Checks if this view introduces
* a cycle or max diameter. If an error is detected, it will not insert.
*/
Status insertAndValidate(const NamespaceString& viewNss,
const std::vector<NamespaceString>& refs);
/**
* Called when view definitions are being reloaded from the catalog (e.g. on restart of mongod).
* Does the same as insertAndValidate except does not check for cycles or max diameter.
*/
void insertWithoutValidating(const NamespaceString& viewNss,
const std::vector<NamespaceString>& refs);
/**
* Called when a view is removed from the catalog. If the view does not exist in the graph it is
* a no-op. The view may also have a cycle or max diameter through it.
*/
void remove(const NamespaceString& viewNss);
/**
* Deletes the view graph and all references to namespaces.
*/
void clear();
private:
// A graph node represents a namespace. The parent-child relation is defined as a parent
// references the child either through viewOn or in $lookup/$graphLookup/$facet in its pipeline.
// E.g. the command {create: "a", viewOn: "b", pipeline: [{$lookup: {from: "c"}}]}
// means the node for "a" is a parent of nodes for "b" and "c" since it references them.
struct Node {
// Note, a view may refer to the same child more than once, but we only need to know the
// set of children and parents, since we do not need to traverse duplicates.
stdx::unordered_set<uint64_t> parents;
stdx::unordered_set<uint64_t> children;
std::string ns;
};
// Bookkeeping for graph traversals.
struct NodeHeight {
bool checked = false;
int height = 0;
};
using HeightMap = stdx::unordered_map<uint64_t, NodeHeight>;
/**
* Recursively traverses parents of this node and computes their heights. Returns an error
* if the maximum depth is exceeded.
*/
ErrorCodes::Error _getParentsHeight(uint64_t currentId, int currentDepth, HeightMap* heightMap);
/**
* Recursively traverses children of the starting node and computes their heights. Returns an
* error if the maximum depth is exceeded or a cycle is detected through the starting node.
*/
ErrorCodes::Error _getChildrenHeightAndCheckCycle(uint64_t startingId,
uint64_t currentId,
int currentDepth,
HeightMap* heightMap,
std::vector<uint64_t>* cycleIds);
/**
* Gets the id for this namespace, and creates an id if it doesn't exist.
*/
uint64_t _getNodeId(const NamespaceString& ns);
// Maps namespaces to an internal node id. A mapping exists for every namespace referenced,
// i.e. existing views, collections, and non-existing namespaces.
StringMap<uint64_t> _namespaceIds;
// Maps node ids to nodes. There is a 1-1 correspondance with _namespaceIds, hence the lifetime
// of a node is the same as the lifetime as its corresponding node id.
stdx::unordered_map<uint64_t, Node> _graph;
static uint64_t _idCounter;
};
} // namespace mongo
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