1MONGOC_DATABASE_AGGREGATE(3) libmongoc MONGOC_DATABASE_AGGREGATE(3)
2
6 mongoc_cursor_t *
7 mongoc_database_aggregate (mongoc_database_t *database,
8 const bson_t *pipeline,
9 const bson_t *opts,
10 const mongoc_read_prefs_t *read_prefs)
11 BSON_GNUC_WARN_UNUSED_RESULT;
12
14 • database: A mongoc_database_t.
15 • pipeline: A bson_t, either a BSON array or a BSON document containing
17 an array field named "pipeline".
18 • opts: A bson_t containing options for the command, or NULL.
20 • read_prefs: A mongoc_read_prefs_t or NULL.
22 opts may be NULL or a BSON document with additional command options:
24 • readConcern: Construct a mongoc_read_concern_t and use
26 mongoc_read_concern_append() to add the read concern to opts. See the
27 example code for mongoc_client_read_command_with_opts(). Read concern
28 requires MongoDB 3.2 or later, otherwise an error is returned.
29 • writeConcern: Construct a mongoc_write_concern_t and use
31 mongoc_write_concern_append() to add the write concern to opts. See
32 the example code for mongoc_client_write_command_with_opts().
33 • sessionId: First, construct a mongoc_client_session_t with
35 mongoc_client_start_session(). You can begin a transaction with
36 mongoc_client_session_start_transaction(), optionally with a
37 mongoc_transaction_opt_t that overrides the options inherited from
38 database, and use mongoc_client_session_append() to add the session
39 to opts. See the example code for mongoc_client_session_t.
40 • bypassDocumentValidation: Set to true to skip server-side schema val‐
42 idation of the provided BSON documents.
43 • collation: Configure textual comparisons. See Setting Collation Or‐
45 der, and the MongoDB Manual entry on Collation. Collation requires
46 MongoDB 3.2 or later, otherwise an error is returned.
47 • serverId: To target a specific server, include an int32 "serverId"
49 field. Obtain the id by calling mongoc_client_select_server(), then
50 mongoc_server_description_id() on its return value.
51 • batchSize: An int32 representing number of documents requested to be
53 returned on each call to mongoc_cursor_next()
54 • let: A BSON document consisting of any number of parameter names,
56 each followed by definitions of constants in the MQL Aggregate Ex‐
57 pression language.
58 • comment: A bson_value_t specifying the comment to attach to this com‐
60 mand. The comment will appear in log messages, profiler output, and
61 currentOp output. Only string values are supported prior to MongoDB
62 4.4.
63 • hint: A document or string that specifies the index to use to support
65 the query predicate.
66 For a list of all options, see the MongoDB Manual entry on the aggre‐
68 gate command.
69
71 This function creates a cursor which sends the aggregate command on the
72 underlying database 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. Note that the pipeline must
75 start with a compatible stage that does not require an underlying col‐
76 lection (e.g. "$currentOp", "$listLocalSessions").
77 Read preferences, read and write concern, and collation can be overrid‐
79 den by various sources. The highest-priority sources for these options
80 are listed first in the following table. In a transaction, read concern
81 and write concern are prohibited in opts and the read preference must
82 be primary or NULL. Write concern is applied from opts, or if opts has
83 no write concern and the aggregation pipeline includes "$out", the
84 write concern is applied from database.
85 ┌─────────────────┬──────────────┬───────────────┬───────────┐
87 │Read Preferences │ Read Concern │ Write Concern │ Collation │
88 ├─────────────────┼──────────────┼───────────────┼───────────┤
89 │read_prefs │ opts │ opts │ opts │
90 ├─────────────────┼──────────────┼───────────────┼───────────┤
91 │Transaction │ Transaction │ Transaction │ │
92 ├─────────────────┼──────────────┼───────────────┼───────────┤
93 │database │ database │ database │ │
94 └─────────────────┴──────────────┴───────────────┴───────────┘
95 See the example for transactions and for the "distinct" command with
97 opts.
98 This function is considered a retryable read operation unless the pipe‐
100 line contains a write stage like $out or $merge. Upon a transient er‐
101 ror (a network error, errors due to replica set failover, etc.) the op‐
102 eration is safely retried once. If retryreads is false in the URI (see
103 mongoc_uri_t) the retry behavior does not apply.
104
106 This function returns a newly allocated mongoc_cursor_t that should be
107 freed with mongoc_cursor_destroy() when no longer in use. The returned
108 mongoc_cursor_t is never NULL, even on error. The user must call
109 mongoc_cursor_next() on the returned mongoc_cursor_t to execute the
110 initial command.
111 Cursor errors can be checked with mongoc_cursor_error_document(). It
113 always fills out the bson_error_t if an error occurred, and optionally
114 includes a server reply document if the error occurred server-side.
115 WARNING:
117 Failure to handle the result of this function is a programming er‐
118 ror.
119
121 #include <bson/bson.h>
122 #include <mongoc/mongoc.h>
123 static mongoc_cursor_t *
125 current_op_query (mongoc_client_t *client)
126 {
127 mongoc_cursor_t *cursor;
128 mongoc_database_t *database;
129 bson_t *pipeline;
130 pipeline = BCON_NEW ("pipeline",
132 "[",
133 "{",
134 "$currentOp",
135 "{",
136 "}",
137 "}",
138 "]");
139 /* $currentOp must be run on the admin database */
141 database = mongoc_client_get_database (client, "admin");
142 cursor = mongoc_database_aggregate (
144 database, pipeline, NULL, NULL);
145 bson_destroy (pipeline);
147 mongoc_database_destroy (database);
148 return cursor;
150 }
151
153 MongoDB, Inc
154
156 2017-present, MongoDB, Inc
1571.25.1 Nov 08, 2023 MONGOC_DATABASE_AGGREGATE(3)