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 mon‐
33 goc_read_concern_append to add the read concern to opts. See the ex‐
34 ample code for mongoc_client_read_command_with_opts. Read concern re‐
35 quires MongoDB 3.2 or later, otherwise an error is returned.
36 • writeConcern: Construct a mongoc_write_concern_t and use mon‐
38 goc_write_concern_append to add the write concern to opts. See the
39 example code for mongoc_client_write_command_with_opts.
40 • sessionId: First, construct a mongoc_client_session_t with mon‐
42 goc_client_start_session. You can begin a transaction with mon‐
43 goc_client_session_start_transaction, optionally with a mongoc_trans‐
44 action_opt_t that overrides the options inherited from collection,
45 and use mongoc_client_session_append to add the session to opts. See
46 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 For a list of all options, see the MongoDB Manual entry on the aggre‐
63 gate command.
64 This function is considered a retryable read operation unless the pipe‐
66 line contains a write stage like $out or $merge. Upon a transient er‐
67 ror (a network error, errors due to replica set failover, etc.) the op‐
68 eration is safely retried once. If retryreads is false in the URI (see
69 mongoc_uri_t) the retry behavior does not apply.
70
72 This function creates a cursor which sends the aggregate command on the
73 underlying collection upon the first call to mongoc_cursor_next(). For
74 more information on building aggregation pipelines, see the MongoDB
75 Manual entry on the aggregate command.
76 Read preferences, read and write concern, and collation can be overrid‐
78 den by various sources. The highest-priority sources for these options
79 are listed first in the following table. In a transaction, read concern
80 and write concern are prohibited in opts and the read preference must
81 be primary or NULL. Write concern is applied from opts, or if opts has
82 no write concern and the aggregation pipeline includes "$out", the
83 write concern is applied from collection. The write concern is omitted
84 for MongoDB before 3.4.
85 ┌─────────────────┬──────────────┬───────────────┬───────────┐
87 │Read Preferences │ Read Concern │ Write Concern │ Collation │
88 ├─────────────────┼──────────────┼───────────────┼───────────┤
89 │read_prefs │ opts │ opts │ opts │
90 ├─────────────────┼──────────────┼───────────────┼───────────┤
91 │Transaction │ Transaction │ Transaction │ │
92 ├─────────────────┼──────────────┼───────────────┼───────────┤
93 │collection │ collection │ collection │ │
94 └─────────────────┴──────────────┴───────────────┴───────────┘
95 See the example for transactions and for the "distinct" command with
97 opts.
98
100 This function returns a newly allocated mongoc_cursor_t that should be
101 freed with mongoc_cursor_destroy() when no longer in use. The returned
102 mongoc_cursor_t is never NULL; if the parameters are invalid, the
103 bson_error_t in the mongoc_cursor_t is filled out, and the mongoc_cur‐
104 sor_t is returned before the server is selected. The user must call
105 mongoc_cursor_next() on the returned mongoc_cursor_t to execute the ag‐
106 gregation pipeline.
107 WARNING:
109 Failure to handle the result of this function is a programming er‐
110 ror.
111
113 #include <bson/bson.h>
114 #include <mongoc/mongoc.h>
115 static mongoc_cursor_t *
117 pipeline_query (mongoc_collection_t *collection)
118 {
119 mongoc_cursor_t *cursor;
120 bson_t *pipeline;
121 pipeline = BCON_NEW ("pipeline",
123 "[",
124 "{",
125 "$match",
126 "{",
127 "foo",
128 BCON_UTF8 ("A"),
129 "}",
130 "}",
131 "{",
132 "$match",
133 "{",
134 "bar",
135 BCON_BOOL (false),
136 "}",
137 "}",
138 "]");
139 cursor = mongoc_collection_aggregate (
141 collection, MONGOC_QUERY_NONE, pipeline, NULL, NULL);
142 bson_destroy (pipeline);
144 return cursor;
146 }
147
149 When using $out, the pipeline stage that writes, the write_concern
150 field of the mongoc_cursor_t will be set to the mongoc_write_concern_t
151 parameter, if it is valid, and applied to the write command when mon‐
152 goc_cursor_next() is called. Pass any other parameters to the aggregate
153 command, besides pipeline, as fields in opts:
154 mongoc_write_concern_t *write_concern = mongoc_write_concern_new ();
156 mongoc_write_concern_set_w (write_concern, 3);
157 pipeline =
159 BCON_NEW ("pipeline", "[", "{", "$out", BCON_UTF8 ("collection2"), "}", "]");
160 opts = BCON_NEW ("bypassDocumentValidation", BCON_BOOL (true));
162 mongoc_write_concern_append (write_concern, opts);
163 cursor = mongoc_collection_aggregate (
165 collection1, MONGOC_QUERY_NONE, pipeline, opts, NULL);
166
168 MongoDB, Inc
169
171 2017-present, MongoDB, Inc
1721.17.6 Jun 03, 2021 MONGOC_COLLECTION_AGGREGATE(3)