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 <string>
34 
35 #include "mongo/base/status.h"
36 #include "mongo/db/hasher.h"  // For HashSeed.
37 #include "mongo/db/index/index_access_method.h"
38 #include "mongo/db/index/index_descriptor.h"
39 #include "mongo/db/jsobj.h"
40 
41 namespace mongo {
42 
43 class CollatorInterface;
44 
45 /**
46  * This is the access method for "hashed" indices.
47  */
48 class HashAccessMethod : public IndexAccessMethod {
49 public:
50     HashAccessMethod(IndexCatalogEntry* btreeState, SortedDataInterface* btree);
51 
52 private:
53     /**
54      * Fills 'keys' with the keys that should be generated for 'obj' on this index.
55      *
56      * This function ignores the 'multikeyPaths' pointer because hashed indexes don't support
57      * tracking path-level multikey information.
58      */
59     void doGetKeys(const BSONObj& obj,
60                    GetKeysContext context,
61                    BSONObjSet* keys,
62                    MultikeyPaths* multikeyPaths) const final;
63 
64     // Only one of our fields is hashed.  This is the field name for it.
65     std::string _hashedField;
66 
67     // _seed defaults to zero.
68     HashSeed _seed;
69 
70     // _hashVersion defaults to zero.
71     int _hashVersion;
72 
73     BSONObj _missingKey;
74 
75     // Null if this index orders strings according to the simple binary compare. If non-null,
76     // represents the collator used to generate index keys for indexed strings.
77     const CollatorInterface* _collator;
78 };
79 
80 }  // namespace mongo
81