# mongoc_client_t

## MongoDB Connection Abstraction

## Synopsis

    typedef struct _mongoc_client_t mongoc_client_t;

    typedef mongoc_stream_t *
    (*mongoc_stream_initiator_t) (const mongoc_uri_t       *uri,
                                  const mongoc_host_list_t *host,
                                  void                     *user_data,
                                  bson_error_t             *error);

mongoc_client_t is an opaque type that provides access to a MongoDB node, replica-set, or sharded-cluster. It maintains management of underlying sockets and routing to individual nodes based on mongoc_read_prefs_t or mongoc_write_concern_t.

## Streams

The underlying transport for a given client can be customized, wrapped or replaced by any implementation that fulfills mongoc_stream_t. A custom transport can be set with mongoc_client_set_stream_initiator().

## Thread Safety

mongoc_client_t is NOT thread-safe and should only be used from one thread at a time. When used in multi-threaded scenarios, it is recommended that you use the thread-safe mongoc_client_pool_t to retrieve a mongoc_client_t for your thread.

## Lifecycle

It is an error to call mongoc_client_destroy on a client that has operations pending. It is required that you release mongoc_collection_t and mongoc_database_t structures before calling mongoc_client_destroy.

## Example

    /* gcc example.c -o example $(pkg-config --cflags --libs libmongoc-1.0) */

    /* ./example-client [CONNECTION_STRING [COLLECTION_NAME]] */

    #include <mongoc.h>
    #include <stdio.h>
    #include <stdlib.h>

    int
    main (int   argc,
          char *argv[])
    {
       mongoc_client_t *client;
       mongoc_collection_t *collection;
       mongoc_cursor_t *cursor;
       bson_error_t error;
       const bson_t *doc;
       const char *uristr = "mongodb://127.0.0.1/";
       const char *collection_name = "test";
       bson_t query;
       char *str;

       mongoc_init ();

       if (argc > 1) {
          uristr = argv [1];
       }

       if (argc > 2) {
          collection_name = argv [2];
       }

       client = mongoc_client_new (uristr);

       if (!client) {
          fprintf (stderr, "Failed to parse URI.\n");
          return EXIT_FAILURE;
       }

       bson_init (&query);

    #if 0
       bson_append_utf8 (&query, "hello", -1, "world", -1);
    #endif

       collection = mongoc_client_get_collection (client, "test", collection_name);
       cursor = mongoc_collection_find (collection,
                                        MONGOC_QUERY_NONE,
                                        0,
                                        0,
                                        0,
                                        &query,
                                        NULL,  /* Fields, NULL for all. */
                                        NULL); /* Read Prefs, NULL for default */

       while (mongoc_cursor_next (cursor, &doc)) {
          str = bson_as_json (doc, NULL);
          fprintf (stdout, "%s\n", str);
          bson_free (str);
       }

       if (mongoc_cursor_error (cursor, &error)) {
          fprintf (stderr, "Cursor Failure: %s\n", error.message);
          return EXIT_FAILURE;
       }

       bson_destroy (&query);
       mongoc_cursor_destroy (cursor);
       mongoc_collection_destroy (collection);
       mongoc_client_destroy (client);

       mongoc_cleanup ();

       return EXIT_SUCCESS;
    }