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 • 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 For a list of all options, see the MongoDB Manual entry on the aggre‐
67 gate command.
68 This function is considered a retryable read operation unless the pipe‐
70 line contains a write stage like $out or $merge. Upon a transient er‐
71 ror (a network error, errors due to replica set failover, etc.) the op‐
72 eration is safely retried once. If retryreads is false in the URI (see
73 mongoc_uri_t) the retry behavior does not apply.
74
76 This function creates a cursor which sends the aggregate command on the
77 underlying collection upon the first call to mongoc_cursor_next(). For
78 more information on building aggregation pipelines, see the MongoDB
79 Manual entry on the aggregate command.
80 Read preferences, read and write concern, and collation can be overrid‐
82 den by various sources. The highest-priority sources for these options
83 are listed first in the following table. In a transaction, read concern
84 and write concern are prohibited in opts and the read preference must
85 be primary or NULL. Write concern is applied from opts, or if opts has
86 no write concern and the aggregation pipeline includes "$out", the
87 write concern is applied from collection. The write concern is omitted
88 for MongoDB before 3.4.
89 ┌─────────────────┬──────────────┬───────────────┬───────────┐
91 │Read Preferences │ Read Concern │ Write Concern │ Collation │
92 ├─────────────────┼──────────────┼───────────────┼───────────┤
93 │read_prefs │ opts │ opts │ opts │
94 ├─────────────────┼──────────────┼───────────────┼───────────┤
95 │Transaction │ Transaction │ Transaction │ │
96 ├─────────────────┼──────────────┼───────────────┼───────────┤
97 │collection │ collection │ collection │ │
98 └─────────────────┴──────────────┴───────────────┴───────────┘
99 See the example for transactions and for the "distinct" command with
101 opts.
102
104 This function returns a newly allocated mongoc_cursor_t that should be
105 freed with mongoc_cursor_destroy() when no longer in use. The returned
106 mongoc_cursor_t is never NULL, even on error. The user must call mon‐
107 goc_cursor_next() on the returned mongoc_cursor_t to execute the ini‐
108 tial command.
109 Cursor errors can be checked with mongoc_cursor_error_document. It al‐
111 ways fills out the bson_error_t if an error occurred, and optionally
112 includes a server reply document if the error occurred server-side.
113 WARNING:
115 Failure to handle the result of this function is a programming er‐
116 ror.
117
119 #include <bson/bson.h>
120 #include <mongoc/mongoc.h>
121 static mongoc_cursor_t *
123 pipeline_query (mongoc_collection_t *collection)
124 {
125 mongoc_cursor_t *cursor;
126 bson_t *pipeline;
127 pipeline = BCON_NEW ("pipeline",
129 "[",
130 "{",
131 "$match",
132 "{",
133 "foo",
134 BCON_UTF8 ("A"),
135 "}",
136 "}",
137 "{",
138 "$match",
139 "{",
140 "bar",
141 BCON_BOOL (false),
142 "}",
143 "}",
144 "]");
145 cursor = mongoc_collection_aggregate (
147 collection, MONGOC_QUERY_NONE, pipeline, NULL, NULL);
148 bson_destroy (pipeline);
150 return cursor;
152 }
153
155 When using $out, the pipeline stage that writes, the write_concern
156 field of the mongoc_cursor_t will be set to the mongoc_write_concern_t
157 parameter, if it is valid, and applied to the write command when mon‐
158 goc_cursor_next() is called. Pass any other parameters to the aggregate
159 command, besides pipeline, as fields in opts:
160 mongoc_write_concern_t *write_concern = mongoc_write_concern_new ();
162 mongoc_write_concern_set_w (write_concern, 3);
163 pipeline =
165 BCON_NEW ("pipeline", "[", "{", "$out", BCON_UTF8 ("collection2"), "}", "]");
166 opts = BCON_NEW ("bypassDocumentValidation", BCON_BOOL (true));
168 mongoc_write_concern_append (write_concern, opts);
169 cursor = mongoc_collection_aggregate (
171 collection1, MONGOC_QUERY_NONE, pipeline, opts, NULL);
172
174 MongoDB, Inc
175
177 2017-present, MongoDB, Inc
1781.21.1 Mar 02, 2022 MONGOC_COLLECTION_AGGREGATE(3)