1MONGOC_DATABASE_AGGREGATE(3) libmongoc MONGOC_DATABASE_AGGREGATE(3)
2
6 mongoc_database_aggregate - mongoc_database_aggregate()
7
9 mongoc_cursor_t *
10 mongoc_database_aggregate (mongoc_database_t *database,
11 const bson_t *pipeline,
12 const bson_t *opts,
13 const mongoc_read_prefs_t *read_prefs)
14 BSON_GNUC_WARN_UNUSED_RESULT;
15
17 • database: A mongoc_database_t.
18 • pipeline: A bson_t, either a BSON array or a BSON document containing
20 an array field named "pipeline".
21 • opts: A bson_t containing options for the command, or NULL.
23 • read_prefs: A mongoc_read_prefs_t or NULL.
25 opts may be NULL or a BSON document with additional command options:
27 • readConcern: Construct a mongoc_read_concern_t and use mon‐
29 goc_read_concern_append to add the read concern to opts. See the ex‐
30 ample code for mongoc_client_read_command_with_opts. Read concern re‐
31 quires MongoDB 3.2 or later, otherwise an error is returned.
32 • writeConcern: Construct a mongoc_write_concern_t and use mon‐
34 goc_write_concern_append to add the write concern to opts. See the
35 example code for mongoc_client_write_command_with_opts.
36 • sessionId: First, construct a mongoc_client_session_t with mon‐
38 goc_client_start_session. You can begin a transaction with mon‐
39 goc_client_session_start_transaction, optionally with a mongoc_trans‐
40 action_opt_t that overrides the options inherited from database, and
41 use mongoc_client_session_append to add the session to opts. See the
42 example code for mongoc_client_session_t.
43 • bypassDocumentValidation: Set to true to skip server-side schema val‐
45 idation of the provided BSON documents.
46 • collation: Configure textual comparisons. See Setting Collation Or‐
48 der, and the MongoDB Manual entry on Collation. Collation requires
49 MongoDB 3.2 or later, otherwise an error is returned.
50 • serverId: To target a specific server, include an int32 "serverId"
52 field. Obtain the id by calling mongoc_client_select_server, then
53 mongoc_server_description_id on its return value.
54 • batchSize: An int32 representing number of documents requested to be
56 returned on each call to mongoc_cursor_next
57 • let: A BSON document consisting of any number of parameter names,
59 each followed by definitions of constants in the MQL Aggregate Ex‐
60 pression language
61 For a list of all options, see the MongoDB Manual entry on the aggre‐
63 gate command.
64
66 This function creates a cursor which sends the aggregate command on the
67 underlying database upon the first call to mongoc_cursor_next(). For
68 more information on building aggregation pipelines, see the MongoDB
69 Manual entry on the aggregate command. Note that the pipeline must
70 start with a compatible stage that does not require an underlying col‐
71 lection (e.g. "$currentOp", "$listLocalSessions").
72 Read preferences, read and write concern, and collation can be overrid‐
74 den by various sources. The highest-priority sources for these options
75 are listed first in the following table. In a transaction, read concern
76 and write concern are prohibited in opts and the read preference must
77 be primary or NULL. Write concern is applied from opts, or if opts has
78 no write concern and the aggregation pipeline includes "$out", the
79 write concern is applied from database.
80 ┌─────────────────┬──────────────┬───────────────┬───────────┐
82 │Read Preferences │ Read Concern │ Write Concern │ Collation │
83 ├─────────────────┼──────────────┼───────────────┼───────────┤
84 │read_prefs │ opts │ opts │ opts │
85 ├─────────────────┼──────────────┼───────────────┼───────────┤
86 │Transaction │ Transaction │ Transaction │ │
87 ├─────────────────┼──────────────┼───────────────┼───────────┤
88 │database │ database │ database │ │
89 └─────────────────┴──────────────┴───────────────┴───────────┘
90 See the example for transactions and for the "distinct" command with
92 opts.
93 This function is considered a retryable read operation unless the pipe‐
95 line contains a write stage like $out or $merge. Upon a transient er‐
96 ror (a network error, errors due to replica set failover, etc.) the op‐
97 eration is safely retried once. If retryreads is false in the URI (see
98 mongoc_uri_t) the retry behavior does not apply.
99
101 This function returns a newly allocated mongoc_cursor_t that should be
102 freed with mongoc_cursor_destroy() when no longer in use. The returned
103 mongoc_cursor_t is never NULL, even on error. The user must call mon‐
104 goc_cursor_next() on the returned mongoc_cursor_t to execute the ini‐
105 tial command.
106 Cursor errors can be checked with mongoc_cursor_error_document. It al‐
108 ways fills out the bson_error_t if an error occurred, and optionally
109 includes a server reply document if the error occurred server-side.
110 WARNING:
112 Failure to handle the result of this function is a programming er‐
113 ror.
114
116 #include <bson/bson.h>
117 #include <mongoc/mongoc.h>
118 static mongoc_cursor_t *
120 current_op_query (mongoc_client_t *client)
121 {
122 mongoc_cursor_t *cursor;
123 mongoc_database_t *database;
124 bson_t *pipeline;
125 pipeline = BCON_NEW ("pipeline",
127 "[",
128 "{",
129 "$currentOp",
130 "{",
131 "}",
132 "}",
133 "]");
134 /* $currentOp must be run on the admin database */
136 database = mongoc_client_get_database (client, "admin");
137 cursor = mongoc_database_aggregate (
139 database, pipeline, NULL, NULL);
140 bson_destroy (pipeline);
142 mongoc_database_destroy (database);
143 return cursor;
145 }
146
148 MongoDB, Inc
149
151 2017-present, MongoDB, Inc
1521.20.0 Nov 18, 2021 MONGOC_DATABASE_AGGREGATE(3)