1 
2 /**
3  *    Copyright (C) 2018-present MongoDB, Inc.
4  *
5  *    This program is free software: you can redistribute it and/or modify
6  *    it under the terms of the Server Side Public License, version 1,
7  *    as published by MongoDB, Inc.
8  *
9  *    This program is distributed in the hope that it will be useful,
10  *    but WITHOUT ANY WARRANTY; without even the implied warranty of
11  *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12  *    Server Side Public License for more details.
13  *
14  *    You should have received a copy of the Server Side Public License
15  *    along with this program. If not, see
16  *    <http://www.mongodb.com/licensing/server-side-public-license>.
17  *
18  *    As a special exception, the copyright holders give permission to link the
19  *    code of portions of this program with the OpenSSL library under certain
20  *    conditions as described in each individual source file and distribute
21  *    linked combinations including the program with the OpenSSL library. You
22  *    must comply with the Server Side Public License in all respects for
23  *    all of the code used other than as permitted herein. If you modify file(s)
24  *    with this exception, you may extend this exception to your version of the
25  *    file(s), but you are not obligated to do so. If you do not wish to do so,
26  *    delete this exception statement from your version. If you delete this
27  *    exception statement from all source files in the program, then also delete
28  *    it in the license file.
29  */
30 
31 #pragma once
32 
33 #include <boost/optional.hpp>
34 #include <set>
35 #include <string>
36 
37 #include "mongo/db/pipeline/document.h"
38 #include "mongo/db/pipeline/variables.h"
39 
40 namespace mongo {
41 class ParsedDeps;
42 
43 /**
44  * This struct allows components in an agg pipeline to report what they need from their input.
45  */
46 struct DepsTracker {
47     /**
48      * Represents what metadata is available on documents that are input to the pipeline.
49      */
50     enum MetadataAvailable { kNoMetadata = 0, kTextScore = 1 };
51 
52     DepsTracker(MetadataAvailable metadataAvailable = kNoMetadata)
_metadataAvailableDepsTracker53         : _metadataAvailable(metadataAvailable) {}
54 
55     /**
56      * Returns a projection object covering the dependencies tracked by this class.
57      */
58     BSONObj toProjection() const;
59 
60     boost::optional<ParsedDeps> toParsedDeps() const;
61 
hasNoRequirementsDepsTracker62     bool hasNoRequirements() const {
63         return fields.empty() && !needWholeDocument && !_needTextScore;
64     }
65 
66     /**
67      * Returns 'true' if any of the DepsTracker's variables appear in the passed 'ids' set.
68      */
hasVariableReferenceToDepsTracker69     bool hasVariableReferenceTo(const std::set<Variables::Id>& ids) const {
70         std::vector<Variables::Id> match;
71         std::set_intersection(
72             vars.begin(), vars.end(), ids.begin(), ids.end(), std::back_inserter(match));
73         return !match.empty();
74     }
75 
getMetadataAvailableDepsTracker76     MetadataAvailable getMetadataAvailable() const {
77         return _metadataAvailable;
78     }
79 
isTextScoreAvailableDepsTracker80     bool isTextScoreAvailable() const {
81         return _metadataAvailable & MetadataAvailable::kTextScore;
82     }
83 
getNeedTextScoreDepsTracker84     bool getNeedTextScore() const {
85         return _needTextScore;
86     }
87 
setNeedTextScoreDepsTracker88     void setNeedTextScore(bool needTextScore) {
89         if (needTextScore && !isTextScoreAvailable()) {
90             uasserted(
91                 40218,
92                 "pipeline requires text score metadata, but there is no text score available");
93         }
94         _needTextScore = needTextScore;
95     }
96 
getNeedSortKeyDepsTracker97     bool getNeedSortKey() const {
98         return _needSortKey;
99     }
100 
setNeedSortKeyDepsTracker101     void setNeedSortKey(bool needSortKey) {
102         // We don't expect to ever unset '_needSortKey'.
103         invariant(!_needSortKey || needSortKey);
104         _needSortKey = needSortKey;
105     }
106 
107     std::set<std::string> fields;    // Names of needed fields in dotted notation.
108     std::set<Variables::Id> vars;    // IDs of referenced variables.
109     bool needWholeDocument = false;  // If true, ignore 'fields'; the whole document is needed.
110 
111 private:
112     /**
113      * Appends the meta projections for the sort key and/or text score to 'bb' if necessary. Returns
114      * true if either type of metadata was needed, and false otherwise.
115      */
116     bool _appendMetaProjections(BSONObjBuilder* bb) const;
117 
118     MetadataAvailable _metadataAvailable;
119     bool _needTextScore = false;  // if true, add a {$meta: "textScore"} to the projection.
120     bool _needSortKey = false;    // if true, add a {$meta: "sortKey"} to the projection.
121 };
122 
123 /**
124  * This class is designed to quickly extract the needed fields from a BSONObj into a Document.
125  * It should only be created by a call to DepsTracker::ParsedDeps
126  */
127 class ParsedDeps {
128 public:
129     Document extractFields(const BSONObj& input) const;
130 
131 private:
132     friend struct DepsTracker;  // so it can call constructor
ParsedDeps(Document && fields)133     explicit ParsedDeps(Document&& fields) : _fields(std::move(fields)), _nFields(_fields.size()) {}
134 
135     Document _fields;
136     int _nFields;  // Cache the number of top-level fields needed.
137 };
138 }
139