1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
|
/**
* Copyright (C) 2018-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.h"
#include "mongo/db/pipeline/document_source_limit.h"
#include "mongo/db/pipeline/document_source_sort.h"
#include "mongo/db/pipeline/field_path.h"
namespace mongo {
class DocumentSourceUnwind final : public DocumentSource {
public:
static constexpr StringData kStageName = "$unwind"_sd;
// virtuals from DocumentSource
const char* getSourceName() const final;
Value serialize(SerializationOptions opts = SerializationOptions()) const final override;
/**
* Returns the unwound path, and the 'includeArrayIndex' path, if specified.
*/
GetModPathsReturn getModifiedPaths() const final;
StageConstraints constraints(Pipeline::SplitState pipeState) const final {
StageConstraints constraints(StreamType::kStreaming,
PositionRequirement::kNone,
HostTypeRequirement::kNone,
DiskUseRequirement::kNoDiskUse,
FacetRequirement::kAllowed,
TransactionRequirement::kAllowed,
LookupRequirement::kAllowed,
UnionRequirement::kAllowed);
constraints.canSwapWithMatch = true;
return constraints;
}
boost::optional<DistributedPlanLogic> distributedPlanLogic() final {
return boost::none;
}
DepsTracker::State getDependencies(DepsTracker* deps) const final;
void addVariableRefs(std::set<Variables::Id>* refs) const final {}
/**
* Creates a new $unwind DocumentSource from a BSON specification.
*/
static boost::intrusive_ptr<DocumentSource> createFromBson(
BSONElement elem, const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
static boost::intrusive_ptr<DocumentSourceUnwind> create(
const boost::intrusive_ptr<ExpressionContext>& expCtx,
const std::string& path,
bool includeNullIfEmptyOrMissing,
const boost::optional<std::string>& includeArrayIndex,
bool strict = false);
std::string getUnwindPath() const {
return _unwindPath.fullPath();
}
bool preserveNullAndEmptyArrays() const {
return _preserveNullAndEmptyArrays;
}
const boost::optional<FieldPath>& indexPath() const {
return _indexPath;
}
protected:
/**
* Attempts to swap with a subsequent $sort stage if the $sort is on a different field.
*/
Pipeline::SourceContainer::iterator doOptimizeAt(Pipeline::SourceContainer::iterator itr,
Pipeline::SourceContainer* container) final;
private:
DocumentSourceUnwind(const boost::intrusive_ptr<ExpressionContext>& pExpCtx,
const FieldPath& fieldPath,
bool includeNullIfEmptyOrMissing,
const boost::optional<FieldPath>& includeArrayIndex,
bool strict);
GetNextResult doGetNext() final;
// Checks if a sort is eligible to be moved before the unwind.
bool canPushSortBack(const DocumentSourceSort* sort) const;
// Checks if a limit is eligible to be moved before the unwind.
bool canPushLimitBack(const DocumentSourceLimit* limit) const;
// Configuration state.
const FieldPath _unwindPath;
// Documents that have a nullish value, or an empty array for the field '_unwindPath', will pass
// through the $unwind stage unmodified if '_preserveNullAndEmptyArrays' is true.
const bool _preserveNullAndEmptyArrays;
// If set, the $unwind stage will include the array index in the specified path, overwriting any
// existing value, setting to null when the value was a non-array or empty array.
const boost::optional<FieldPath> _indexPath;
// Iteration state.
class Unwinder;
std::unique_ptr<Unwinder> _unwinder;
// If preserveNullAndEmptyArrays is true and unwind is followed by a limit, we can duplicate
// the limit before the unwind. We only want to do this if we've found a limit smaller than the
// one we already pushed down. boost::none means no push down has occurred yet.
boost::optional<long long> _smallestLimitPushedDown;
};
/** Helper class to unwind array from a single document. */
class DocumentSourceUnwind::Unwinder {
public:
Unwinder(const FieldPath& unwindPath,
bool preserveNullAndEmptyArrays,
const boost::optional<FieldPath>& indexPath,
bool strict);
/** Reset the unwinder to unwind a new document. */
void resetDocument(const Document& document);
/**
* @return the next document unwound from the document provided to resetDocument(), using
* the current value in the array located at the provided unwindPath.
*
* Returns boost::none if the array is exhausted.
*/
DocumentSource::GetNextResult getNext();
private:
// Tracks whether or not we can possibly return any more documents. Note we may return
// boost::none even if this is true.
bool _haveNext = false;
// Path to the array to unwind.
const FieldPath _unwindPath;
// Documents that have a nullish value, or an empty array for the field '_unwindPath', will pass
// through the $unwind stage unmodified if '_preserveNullAndEmptyArrays' is true.
const bool _preserveNullAndEmptyArrays;
// If set, the $unwind stage will include the array index in the specified path, overwriting any
// existing value, setting to null when the value was a non-array or empty array.
const boost::optional<FieldPath> _indexPath;
// Specifies if input to $unwind is required to be an array.
const bool _strict;
Value _inputArray;
MutableDocument _output;
// Document indexes of the field path components.
std::vector<Position> _unwindPathFieldIndexes;
// Index into the _inputArray to return next.
size_t _index = 0;
};
} // namespace mongo
|
