MONGOC_CLIENT_...MAND_WITH_OPTS(3)

okay so bestie, this is the MONGOC_CLIENT_...MAND_WITH_OPTS(3) page from libmongoc, and it's literally about mongoc_client_read_command_with_opts(). The whole vibe is “run a read-y command, but let the library do its version-aware little magic.” ✨

🎀 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);

So this function executes a command on the server and applies the logic that is specific to commands that read, while taking the MongoDB server version into account. If you want to send a raw command to the server with none of that logic, use mongoc_client_command_simple() instead. 🫶

Use this one for commands that read, like "count" or "distinct". Read preferences, read concern, and collation can all be overridden by various sources, and the highest-priority sources for these options are listed first. In a transaction, read concern and write concern are prohibited in opts, and the read preference must be primary or NULL. Also: no write concern is applied. ⚠️

priority check, bestie — highest-priority sources first:

1. Read Preferences: read_prefs; Read Concern: opts; Collation: opts.
2. Read Preferences: Transaction; Read Concern: Transaction; Collation: blank in the original table.
3. Read Preferences: client; Read Concern: blank in the original table; Collation: blank in the original table.

See the example for transactions and for the "distinct" command with opts. 🦋

reply is always initialized, and must be freed with bson_destroy(). no cap.

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. 💅

🫶 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 overwritable storage 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 Setting Collation Order, and the MongoDB Manual entry on Collation. 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 the MongoDB Manual entry on Database Commands for each command's arguments. 📚

💀 ERRORS 💀

Errors are propagated via the error parameter.

🌈 RETURNS 🌈

Returns true if successful. Returns false and sets error if there are invalid arguments or a server or network error.

🍓 EXAMPLE 🍓

This is the example file, and the code is staying exactly as-is because it's iconic:

          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:\n"
                        "error message: %s\n",
                        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;
          }

👑 AUTHOR 👑

MongoDB, Inc

🎀 COPYRIGHT 🎀

2009-present, MongoDB, Inc.

okay bye bestie! 💖 source/version: libmongoc 2.5.6; date: Oct 09, 202 (yep, that's how the footer date reads before it runs into MONGOC_CLIENT_...MAND_WITH_OPTS(3)). slay and happy reading! 🎀✨