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.
21 · pipeline: A bson_t, either a BSON array or a BSON document containing
23 an array field named "pipeline".
24 · opts: A bson_t containing options for the command, or NULL.
26 · read_prefs: A mongoc_read_prefs_t or NULL.
28 opts may be NULL or a BSON document with additional command options:
30 · readConcern: Construct a mongoc_read_concern_t and use mon‐
32 goc_read_concern_append to add the read concern to opts. See the
33 example code for mongoc_client_read_command_with_opts. Read concern
34 requires MongoDB 3.2 or later, otherwise an error is returned.
35 · writeConcern: Construct a mongoc_write_concern_t and use mon‐
37 goc_write_concern_append to add the write concern to opts. See the
38 example code for mongoc_client_write_command_with_opts.
39 · sessionId: First, construct a mongoc_client_session_t with mon‐
41 goc_client_start_session. You can begin a transaction with mon‐
42 goc_client_session_start_transaction, optionally with a mongoc_trans‐
43 action_opt_t that overrides the options inherited from collection,
44 and use mongoc_client_session_append to add the session to opts. See
45 the example code for mongoc_client_session_t.
46 · bypassDocumentValidation: Set to true to skip server-side schema val‐
48 idation of the provided BSON documents.
49 · collation: Configure textual comparisons. See Setting Collation
51 Order, and the MongoDB Manual entry on Collation. Collation requires
52 MongoDB 3.2 or later, otherwise an error is returned.
53 · serverId: To target a specific server, include an int32 "serverId"
55 field. Obtain the id by calling mongoc_client_select_server, then
56 mongoc_server_description_id on its return value.
57 · batchSize: An int32 representing number of documents requested to be
59 returned on each call to mongoc_cursor_next
60 For a list of all options, see the MongoDB Manual entry on the aggre‐
62 gate command.
63 This function is considered a retryable read operation unless the pipe‐
65 line contains a write stage like $out or $merge. Upon a transient
66 error (a network error, errors due to replica set failover, etc.) the
67 operation is safely retried once. If retryreads is false in the URI
68 (see mongoc_uri_t) the retry behavior does not apply.
69
71 This function creates a cursor which sends the aggregate command on the
72 underlying collection upon the first call to mongoc_cursor_next(). For
73 more information on building aggregation pipelines, see the MongoDB
74 Manual entry on the aggregate command.
75 Read preferences, read and write concern, and collation can be overrid‐
77 den by various sources. The highest-priority sources for these options
78 are listed first in the following table. In a transaction, read concern
79 and write concern are prohibited in opts and the read preference must
80 be primary or NULL. Write concern is applied from opts, or if opts has
81 no write concern and the aggregation pipeline includes "$out", the
82 write concern is applied from collection. The write concern is omitted
83 for MongoDB before 3.4.
84 ┌─────────────────┬──────────────┬───────────────┬───────────┐
86 │Read Preferences │ Read Concern │ Write Concern │ Collation │
87 ├─────────────────┼──────────────┼───────────────┼───────────┤
88 │read_prefs │ opts │ opts │ opts │
89 ├─────────────────┼──────────────┼───────────────┼───────────┤
90 │Transaction │ Transaction │ Transaction │ │
91 ├─────────────────┼──────────────┼───────────────┼───────────┤
92 │collection │ collection │ collection │ │
93 └─────────────────┴──────────────┴───────────────┴───────────┘
94 See the example for transactions and for the "distinct" command with
96 opts.
97
99 This function returns a newly allocated mongoc_cursor_t that should be
100 freed with mongoc_cursor_destroy() when no longer in use. The returned
101 mongoc_cursor_t is never NULL; if the parameters are invalid, the
102 bson_error_t in the mongoc_cursor_t is filled out, and the mongoc_cur‐
103 sor_t is returned before the server is selected. The user must call
104 mongoc_cursor_next() on the returned mongoc_cursor_t to execute the
105 aggregation pipeline.
106 WARNING:
108 Failure to handle the result of this function is a programming
109 error.
110
112 #include <bson/bson.h>
113 #include <mongoc/mongoc.h>
114 static mongoc_cursor_t *
116 pipeline_query (mongoc_collection_t *collection)
117 {
118 mongoc_cursor_t *cursor;
119 bson_t *pipeline;
120 pipeline = BCON_NEW ("pipeline",
122 "[",
123 "{",
124 "$match",
125 "{",
126 "foo",
127 BCON_UTF8 ("A"),
128 "}",
129 "}",
130 "{",
131 "$match",
132 "{",
133 "bar",
134 BCON_BOOL (false),
135 "}",
136 "}",
137 "]");
138 cursor = mongoc_collection_aggregate (
140 collection, MONGOC_QUERY_NONE, pipeline, NULL, NULL);
141 bson_destroy (pipeline);
143 return cursor;
145 }
146
148 When using $out, the pipeline stage that writes, the write_concern
149 field of the mongoc_cursor_t will be set to the mongoc_write_concern_t
150 parameter, if it is valid, and applied to the write command when mon‐
151 goc_cursor_next() is called. Pass any other parameters to the aggregate
152 command, besides pipeline, as fields in opts:
153 mongoc_write_concern_t *write_concern = mongoc_write_concern_new ();
155 mongoc_write_concern_set_w (write_concern, 3);
156 pipeline =
158 BCON_NEW ("pipeline", "[", "{", "$out", BCON_UTF8 ("collection2"), "}", "]");
159 opts = BCON_NEW ("bypassDocumentValidation", BCON_BOOL (true));
161 mongoc_write_concern_append (write_concern, opts);
162 cursor = mongoc_collection_aggregate (
164 collection1, MONGOC_QUERY_NONE, pipeline, opts, NULL);
165
167 MongoDB, Inc
168
170 2017-present, MongoDB, Inc
1711.16.2 Feb 25, 2020 MONGOC_COLLECTION_AGGREGATE(3)