1MONGOC_COLLECTION_AGGREGATE(3) libmongoc MONGOC_COLLECTION_AGGREGATE(3)
2
6 mongoc_collection_aggregate - mongoc_collection_aggregate()
7
9 mongoc_cursor_t *
10 mongoc_collection_aggregate (mongoc_collection_t *collection,
11 mongoc_query_flags_t flags,
12 const bson_t *pipeline,
13 const bson_t *opts,
14 const mongoc_read_prefs_t *read_prefs)
15 BSON_GNUC_WARN_UNUSED_RESULT;
16
18 • collection: A mongoc_collection_t.
19 • flags: A mongoc_query_flags_t. Not all flag values apply. In particu‐
21 lar, setting MONGOC_QUERY_EXHAUST results in an error.
22 • pipeline: A bson_t, either a BSON array or a BSON document containing
24 an array field named "pipeline".
25 • opts: A bson_t containing options for the command, or NULL.
27 • read_prefs: A mongoc_read_prefs_t or NULL.
29 opts may be NULL or a BSON document with additional command options:
31 • readConcern: Construct a mongoc_read_concern_t and use
33 mongoc_read_concern_append() to add the read concern to opts. See the
34 example code for mongoc_client_read_command_with_opts(). Read concern
35 requires MongoDB 3.2 or later, otherwise an error is returned.
36 • writeConcern: Construct a mongoc_write_concern_t and use
38 mongoc_write_concern_append() to add the write concern to opts. See
39 the example code for mongoc_client_write_command_with_opts().
40 • sessionId: First, construct a mongoc_client_session_t with
42 mongoc_client_start_session(). You can begin a transaction with
43 mongoc_client_session_start_transaction(), optionally with a
44 mongoc_transaction_opt_t that overrides the options inherited from
45 collection, and use mongoc_client_session_append() to add the session
46 to opts. See the example code for mongoc_client_session_t.
47 • bypassDocumentValidation: Set to true to skip server-side schema val‐
49 idation of the provided BSON documents.
50 • collation: Configure textual comparisons. See Setting Collation Or‐
52 der, and the MongoDB Manual entry on Collation. Collation requires
53 MongoDB 3.2 or later, otherwise an error is returned.
54 • serverId: To target a specific server, include an int32 "serverId"
56 field. Obtain the id by calling mongoc_client_select_server(), then
57 mongoc_server_description_id() on its return value.
58 • batchSize: An int32 representing number of documents requested to be
60 returned on each call to mongoc_cursor_next()
61 • let: A BSON document consisting of any number of parameter names,
63 each followed by definitions of constants in the MQL Aggregate Ex‐
64 pression language.
65 • comment: A bson_value_t specifying the comment to attach to this com‐
67 mand. The comment will appear in log messages, profiler output, and
68 currentOp output. Only string values are supported prior to MongoDB
69 4.4.
70 • hint: A document or string that specifies the index to use to support
72 the query predicate.
73 For a list of all options, see the MongoDB Manual entry on the aggre‐
75 gate command.
76 This function is considered a retryable read operation unless the pipe‐
78 line contains a write stage like $out or $merge. Upon a transient er‐
79 ror (a network error, errors due to replica set failover, etc.) the op‐
80 eration is safely retried once. If retryreads is false in the URI (see
81 mongoc_uri_t) the retry behavior does not apply.
82
84 This function creates a cursor which sends the aggregate command on the
85 underlying collection upon the first call to mongoc_cursor_next(). For
86 more information on building aggregation pipelines, see the MongoDB
87 Manual entry on the aggregate command.
88 Read preferences, read and write concern, and collation can be overrid‐
90 den by various sources. The highest-priority sources for these options
91 are listed first in the following table. In a transaction, read concern
92 and write concern are prohibited in opts and the read preference must
93 be primary or NULL. Write concern is applied from opts, or if opts has
94 no write concern and the aggregation pipeline includes "$out", the
95 write concern is applied from collection. The write concern is omitted
96 for MongoDB before 3.4.
97 ┌─────────────────┬──────────────┬───────────────┬───────────┐
99 │Read Preferences │ Read Concern │ Write Concern │ Collation │
100 ├─────────────────┼──────────────┼───────────────┼───────────┤
101 │read_prefs │ opts │ opts │ opts │
102 ├─────────────────┼──────────────┼───────────────┼───────────┤
103 │Transaction │ Transaction │ Transaction │ │
104 ├─────────────────┼──────────────┼───────────────┼───────────┤
105 │collection │ collection │ collection │ │
106 └─────────────────┴──────────────┴───────────────┴───────────┘
107 See the example for transactions and for the "distinct" command with
109 opts.
110
112 This function returns a newly allocated mongoc_cursor_t that should be
113 freed with mongoc_cursor_destroy() when no longer in use. The returned
114 mongoc_cursor_t is never NULL, even on error. The user must call
115 mongoc_cursor_next() on the returned mongoc_cursor_t to execute the
116 initial command.
117 Cursor errors can be checked with mongoc_cursor_error_document(). It
119 always fills out the bson_error_t if an error occurred, and optionally
120 includes a server reply document if the error occurred server-side.
121 WARNING:
123 Failure to handle the result of this function is a programming er‐
124 ror.
125
127 #include <bson/bson.h>
128 #include <mongoc/mongoc.h>
129 static mongoc_cursor_t *
131 pipeline_query (mongoc_collection_t *collection)
132 {
133 mongoc_cursor_t *cursor;
134 bson_t *pipeline;
135 pipeline = BCON_NEW ("pipeline",
137 "[",
138 "{",
139 "$match",
140 "{",
141 "foo",
142 BCON_UTF8 ("A"),
143 "}",
144 "}",
145 "{",
146 "$match",
147 "{",
148 "bar",
149 BCON_BOOL (false),
150 "}",
151 "}",
152 "]");
153 cursor = mongoc_collection_aggregate (
155 collection, MONGOC_QUERY_NONE, pipeline, NULL, NULL);
156 bson_destroy (pipeline);
158 return cursor;
160 }
161
163 When using $out, the pipeline stage that writes, the write_concern
164 field of the mongoc_cursor_t will be set to the mongoc_write_concern_t
165 parameter, if it is valid, and applied to the write command when
166 mongoc_cursor_next() is called. Pass any other parameters to the aggre‐
167 gate command, besides pipeline, as fields in opts:
168 mongoc_write_concern_t *write_concern = mongoc_write_concern_new ();
170 mongoc_write_concern_set_w (write_concern, 3);
171 pipeline =
173 BCON_NEW ("pipeline", "[", "{", "$out", BCON_UTF8 ("collection2"), "}", "]");
174 opts = BCON_NEW ("bypassDocumentValidation", BCON_BOOL (true));
176 mongoc_write_concern_append (write_concern, opts);
177 cursor = mongoc_collection_aggregate (
179 collection1, MONGOC_QUERY_NONE, pipeline, opts, NULL);
180
182 MongoDB, Inc
183
185 2017-present, MongoDB, Inc
1861.24.3 Aug 17, 2023 MONGOC_COLLECTION_AGGREGATE(3)