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 For a list of all options, see the MongoDB Manual entry on the aggre‐
72 gate command.
73 This function is considered a retryable read operation unless the pipe‐
75 line contains a write stage like $out or $merge. Upon a transient er‐
76 ror (a network error, errors due to replica set failover, etc.) the op‐
77 eration is safely retried once. If retryreads is false in the URI (see
78 mongoc_uri_t) the retry behavior does not apply.
79
81 This function creates a cursor which sends the aggregate command on the
82 underlying collection upon the first call to mongoc_cursor_next(). For
83 more information on building aggregation pipelines, see the MongoDB
84 Manual entry on the aggregate command.
85 Read preferences, read and write concern, and collation can be overrid‐
87 den by various sources. The highest-priority sources for these options
88 are listed first in the following table. In a transaction, read concern
89 and write concern are prohibited in opts and the read preference must
90 be primary or NULL. Write concern is applied from opts, or if opts has
91 no write concern and the aggregation pipeline includes "$out", the
92 write concern is applied from collection. The write concern is omitted
93 for MongoDB before 3.4.
94 ┌─────────────────┬──────────────┬───────────────┬───────────┐
96 │Read Preferences │ Read Concern │ Write Concern │ Collation │
97 ├─────────────────┼──────────────┼───────────────┼───────────┤
98 │read_prefs │ opts │ opts │ opts │
99 ├─────────────────┼──────────────┼───────────────┼───────────┤
100 │Transaction │ Transaction │ Transaction │ │
101 ├─────────────────┼──────────────┼───────────────┼───────────┤
102 │collection │ collection │ collection │ │
103 └─────────────────┴──────────────┴───────────────┴───────────┘
104 See the example for transactions and for the "distinct" command with
106 opts.
107
109 This function returns a newly allocated mongoc_cursor_t that should be
110 freed with mongoc_cursor_destroy() when no longer in use. The returned
111 mongoc_cursor_t is never NULL, even on error. The user must call
112 mongoc_cursor_next() on the returned mongoc_cursor_t to execute the
113 initial command.
114 Cursor errors can be checked with mongoc_cursor_error_document(). It
116 always fills out the bson_error_t if an error occurred, and optionally
117 includes a server reply document if the error occurred server-side.
118 WARNING:
120 Failure to handle the result of this function is a programming er‐
121 ror.
122
124 #include <bson/bson.h>
125 #include <mongoc/mongoc.h>
126 static mongoc_cursor_t *
128 pipeline_query (mongoc_collection_t *collection)
129 {
130 mongoc_cursor_t *cursor;
131 bson_t *pipeline;
132 pipeline = BCON_NEW ("pipeline",
134 "[",
135 "{",
136 "$match",
137 "{",
138 "foo",
139 BCON_UTF8 ("A"),
140 "}",
141 "}",
142 "{",
143 "$match",
144 "{",
145 "bar",
146 BCON_BOOL (false),
147 "}",
148 "}",
149 "]");
150 cursor = mongoc_collection_aggregate (
152 collection, MONGOC_QUERY_NONE, pipeline, NULL, NULL);
153 bson_destroy (pipeline);
155 return cursor;
157 }
158
160 When using $out, the pipeline stage that writes, the write_concern
161 field of the mongoc_cursor_t will be set to the mongoc_write_concern_t
162 parameter, if it is valid, and applied to the write command when
163 mongoc_cursor_next() is called. Pass any other parameters to the aggre‐
164 gate command, besides pipeline, as fields in opts:
165 mongoc_write_concern_t *write_concern = mongoc_write_concern_new ();
167 mongoc_write_concern_set_w (write_concern, 3);
168 pipeline =
170 BCON_NEW ("pipeline", "[", "{", "$out", BCON_UTF8 ("collection2"), "}", "]");
171 opts = BCON_NEW ("bypassDocumentValidation", BCON_BOOL (true));
173 mongoc_write_concern_append (write_concern, opts);
174 cursor = mongoc_collection_aggregate (
176 collection1, MONGOC_QUERY_NONE, pipeline, opts, NULL);
177
179 MongoDB, Inc
180
182 2017-present, MongoDB, Inc
1831.23.1 Oct 20, 2022 MONGOC_COLLECTION_AGGREGATE(3)