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1.30.4 Jun 08, 2025 MONGOC_CLIENT_READ_COMMAND_WITH_OPTS(3)
Errors
Errors are propagated via the error parameter.
Example
example-command-with-opts.c
/*
Demonstrates how to prepare options for mongoc_client_read_command_with_opts and
mongoc_client_write_command_with_opts. First it calls "cloneCollectionAsCapped"
command with "writeConcern" option, then "distinct" command with "collation" and
"readConcern" options,
Start a MongoDB 3.4 replica set with --enableMajorityReadConcern and insert two
documents:
$ mongo
MongoDB Enterprise replset:PRIMARY> db.my_collection.insert({x: 1, y: "One"})
WriteResult({ "nInserted" : 1 })
MongoDB Enterprise replset:PRIMARY> db.my_collection.insert({x: 2, y: "Two"})
WriteResult({ "nInserted" : 1 })
Build and run the example:
gcc example-command-with-opts.c -o example-command-with-opts $(pkg-config
--cflags --libs libmongoc-1.0)
./example-command-with-opts [CONNECTION_STRING]
cloneCollectionAsCapped: { "ok" : 1 }
distinct: { "values" : [ 1, 2 ], "ok" : 1 }
*/
#include <mongoc/mongoc.h>
#include <stdio.h>
#include <stdlib.h>
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
const char *uri_string = "mongodb://127.0.0.1/?appname=client-example";
mongoc_uri_t *uri;
bson_t *cmd;
bson_t *opts;
mongoc_write_concern_t *write_concern;
mongoc_read_prefs_t *read_prefs;
mongoc_read_concern_t *read_concern;
bson_t reply;
bson_error_t error;
char *json;
mongoc_init ();
if (argc > 1) {
uri_string = argv[1];
}
uri = mongoc_uri_new_with_error (uri_string, &error);
if (!uri) {
fprintf (stderr,
"failed to parse URI: %s\n"
"error message: %s\n",
uri_string,
error.message);
return EXIT_FAILURE;
}
client = mongoc_client_new_from_uri (uri);
if (!client) {
return EXIT_FAILURE;
}
mongoc_client_set_error_api (client, 2);
cmd = BCON_NEW ("cloneCollectionAsCapped",
BCON_UTF8 ("my_collection"),
"toCollection",
BCON_UTF8 ("my_capped_collection"),
"size",
BCON_INT64 (1024 * 1024));
/* include write concern "majority" in command options */
write_concern = mongoc_write_concern_new ();
mongoc_write_concern_set_wmajority (write_concern, 10000 /* wtimeoutMS */);
opts = bson_new ();
mongoc_write_concern_append (write_concern, opts);
if (mongoc_client_write_command_with_opts (client, "test", cmd, opts, &reply, &error)) {
json = bson_as_canonical_extended_json (&reply, NULL);
printf ("cloneCollectionAsCapped: %s\n", json);
bson_free (json);
} else {
fprintf (stderr, "cloneCollectionAsCapped: %s\n", error.message);
}
bson_free (cmd);
bson_free (opts);
/* distinct values of "x" in "my_collection" where "y" sorts after "one" */
cmd = BCON_NEW ("distinct",
BCON_UTF8 ("my_collection"),
"key",
BCON_UTF8 ("x"),
"query",
"{",
"y",
"{",
"$gt",
BCON_UTF8 ("one"),
"}",
"}");
read_prefs = mongoc_read_prefs_new (MONGOC_READ_SECONDARY);
/* "One" normally sorts before "one"; make "One" sort after "one" */
opts = BCON_NEW ("collation", "{", "locale", BCON_UTF8 ("en_US"), "caseFirst", BCON_UTF8 ("lower"), "}");
/* add a read concern to "opts" */
read_concern = mongoc_read_concern_new ();
mongoc_read_concern_set_level (read_concern, MONGOC_READ_CONCERN_LEVEL_MAJORITY);
mongoc_read_concern_append (read_concern, opts);
if (mongoc_client_read_command_with_opts (client, "test", cmd, read_prefs, opts, &reply, &error)) {
json = bson_as_canonical_extended_json (&reply, NULL);
printf ("distinct: %s\n", json);
bson_free (json);
} else {
fprintf (stderr, "distinct: %s\n", error.message);
}
bson_destroy (cmd);
bson_destroy (opts);
bson_destroy (&reply);
mongoc_read_prefs_destroy (read_prefs);
mongoc_read_concern_destroy (read_concern);
mongoc_write_concern_destroy (write_concern);
mongoc_uri_destroy (uri);
mongoc_client_destroy (client);
mongoc_cleanup ();
return EXIT_SUCCESS;
}
Parameters
• client: A mongoc_client_t.
• db_name: The name of the database to run the command on.
• command: A bson_t containing the command specification.
• read_prefs: An optional mongoc_read_prefs_t.
• opts: A bson_t containing additional options.
• reply: A maybe-NULL pointer to overwritablestorage for a bson_t to contain the results.
• error: An optional location for a bson_error_t or NULL.
opts may be NULL or a BSON document with additional command options:
• readConcern: Construct a mongoc_read_concern_t and use mongoc_read_concern_append() to add the read
concern to opts. See the example code for mongoc_client_read_command_with_opts(). Read concern requires
MongoDB 3.2 or later, otherwise an error is returned.
• sessionId: First, construct a mongoc_client_session_t with mongoc_client_start_session(). You can begin
a transaction with mongoc_client_session_start_transaction(), optionally with a
mongoc_transaction_opt_t that overrides the options inherited from client, and use
mongoc_client_session_append() to add the session to opts. See the example code for
mongoc_client_session_t.
• collation: Configure textual comparisons. See SettingCollationOrder, and theMongoDBManualentryonCollation. Collation requires MongoDB 3.2 or later, otherwise an error is returned.
• serverId: To target a specific server, include an int32 "serverId" field. Obtain the id by calling
mongoc_client_select_server(), then mongoc_server_description_id() on its return value.
Consult theMongoDBManualentryonDatabaseCommands for each command's arguments.
Returns
Returns true if successful. Returns false and sets error if there are invalid arguments or a server or
network error.
Synopsis
bool
mongoc_client_read_command_with_opts (mongoc_client_t *client,
const char *db_name,
const bson_t *command,
const mongoc_read_prefs_t *read_prefs,
const bson_t *opts,
bson_t *reply,
bson_error_t *error);
Execute a command on the server, applying logic that is specific to commands that read, and taking the
MongoDB server version into account. To send a raw command to the server without any of this logic, use
mongoc_client_command_simple().
Use this function for commands that read such as "count" or "distinct".
Read preferences, read concern, and collation can be overridden by various sources. In a transaction,
read concern and write concern are prohibited in opts and the read preference must be primary or NULL.
The highest-priority sources for these options are listed first in the following table. No write concern
is applied.
┌──────────────────┬──────────────┬───────────┐
│ Read Preferences │ Read Concern │ Collation │
├──────────────────┼──────────────┼───────────┤
│ read_prefs │ opts │ opts │
├──────────────────┼──────────────┼───────────┤
│ Transaction │ Transaction │ │
├──────────────────┼──────────────┼───────────┤
│ client │ │ │
└──────────────────┴──────────────┴───────────┘
Seetheexamplefortransactions and for the"distinct"commandwithopts.
reply is always initialized, and must be freed with bson_destroy().
This function is considered a retryable read operation. Upon a transient error (a network error, errors
due to replica set failover, etc.) the operation is safely retried once. If retryreads is false in the
URI (see mongoc_uri_t) the retry behavior does not apply.
Retry logic occurs regardless of the underlying command. Retrying mapReduce has the potential for
degraded performance. Retrying a getMore command has the potential to miss results. For those commands,
use generic command helpers (like mongoc_client_command_with_opts()) instead.
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