1MONGOC_COLLECTION_AGGREGATE(3) MongoDB C Driver 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: For aggregations that include "$out", you can construct
37 a mongoc_write_concern_t and use mongoc_write_concern_append to add
38 the write concern to opts. See the example code for mon‐
39 goc_client_write_command_with_opts.
40 · sessionId: Construct a mongoc_client_session_t with mon‐
42 goc_client_start_session and use mongoc_client_session_append to add
43 the session to opts. See the example code for mongoc_client_ses‐
44 sion_t.
45 · bypassDocumentValidation: Set to true to skip server-side schema val‐
47 idation of the provided BSON documents.
48 · collation: Configure textual comparisons. See Setting Collation
50 Order, and the MongoDB Manual entry on Collation. Collation requires
51 MongoDB 3.2 or later, otherwise an error is returned.
52 · serverId: To target a specific server, include an int32 "serverId"
54 field. Obtain the id by calling mongoc_client_select_server, then
55 mongoc_server_description_id on its return value.
56 · batchSize: To specify the number of documents to return in each batch
58 of a response from the server, include an int "batchSize" field.
59 For a list of all options, see the MongoDB Manual entry on the aggre‐
61 gate command.
62 This function is considered a retryable read operation unless the pipe‐
64 line contains a write stage like $out or $merge. Upon a transient
65 error (a network error, errors due to replica set failover, etc.) the
66 operation is safely retried once. If retryreads is false in the URI
67 (see mongoc_uri_t) the retry behavior does not apply.
68
70 This function creates a cursor which sends the aggregate command on the
71 underlying collection upon the first call to mongoc_cursor_next(). For
72 more information on building aggregation pipelines, see the MongoDB
73 Manual entry on the aggregate command.
74 Read preferences, read and write concern, and collation can be overrid‐
76 den by various sources. The highest-priority sources for these options
77 are listed first in the following table. In a transaction, read concern
78 and write concern are prohibited in opts and the read preference must
79 be primary or NULL. Write concern is applied from opts, or if opts has
80 no write concern and the aggregation pipeline includes "$out", the
81 write concern is applied from collection. The write concern is omitted
82 for MongoDB before 3.4.
83 ┌─────────────────┬──────────────┬───────────────┬───────────┐
85 │Read Preferences │ Read Concern │ Write Concern │ Collation │
86 ├─────────────────┼──────────────┼───────────────┼───────────┤
87 │read_prefs │ opts │ opts │ opts │
88 ├─────────────────┼──────────────┼───────────────┼───────────┤
89 │Transaction │ Transaction │ Transaction │ │
90 ├─────────────────┼──────────────┼───────────────┼───────────┤
91 │collection │ collection │ collection │ │
92 └─────────────────┴──────────────┴───────────────┴───────────┘
93 See the example for transactions and for the "distinct" command with
95 opts.
96
98 This function returns a newly allocated mongoc_cursor_t that should be
99 freed with mongoc_cursor_destroy() when no longer in use. The returned
100 mongoc_cursor_t is never NULL; if the parameters are invalid, the
101 bson_error_t in the mongoc_cursor_t is filled out, and the mongoc_cur‐
102 sor_t is returned before the server is selected. The user must call
103 mongoc_cursor_next() on the returned mongoc_cursor_t to execute the
104 aggregation pipeline.
105 WARNING:
107 Failure to handle the result of this function is a programming
108 error.
109
111 #include <bson/bson.h>
112 #include <mongoc/mongoc.h>
113 static mongoc_cursor_t *
115 pipeline_query (mongoc_collection_t *collection)
116 {
117 mongoc_cursor_t *cursor;
118 bson_t *pipeline;
119 pipeline = BCON_NEW ("pipeline",
121 "[",
122 "{",
123 "$match",
124 "{",
125 "foo",
126 BCON_UTF8 ("A"),
127 "}",
128 "}",
129 "{",
130 "$match",
131 "{",
132 "bar",
133 BCON_BOOL (false),
134 "}",
135 "}",
136 "]");
137 cursor = mongoc_collection_aggregate (
139 collection, MONGOC_QUERY_NONE, pipeline, NULL, NULL);
140 bson_destroy (pipeline);
142 return cursor;
144 }
145
147 When using $out, the pipeline stage that writes, the write_concern
148 field of the mongoc_cursor_t will be set to the mongoc_write_concern_t
149 parameter, if it is valid, and applied to the write command when mon‐
150 goc_cursor_next() is called. Pass any other parameters to the aggregate
151 command, besides pipeline, as fields in opts:
152 mongoc_write_concern_t *write_concern = mongoc_write_concern_new ();
154 mongoc_write_concern_set_w (write_concern, 3);
155 pipeline =
157 BCON_NEW ("pipeline", "[", "{", "$out", BCON_UTF8 ("collection2"), "}", "]");
158 opts = BCON_NEW ("bypassDocumentValidation", BCON_BOOL (true));
160 mongoc_write_concern_append (write_concern, opts);
161 cursor = mongoc_collection_aggregate (
163 collection1, MONGOC_QUERY_NONE, pipeline, opts, NULL);
164
166 MongoDB, Inc
167
169 2017-present, MongoDB, Inc
1701.15.2 Nov 06, 2019 MONGOC_COLLECTION_AGGREGATE(3)