NAME

       mongoc_client_session_t - mongoc_client_session_t

       Use  a  session  for a sequence of operations, optionally with causal consistency. See the MongoDB Manual
       Entry for Causal Consistency.

SYNOPSIS

       Start a session with mongoc_client_start_session, use the  session  for  a  sequence  of  operations  and
       multi-document  transactions,  then  free it with mongoc_client_session_destroy(). Any mongoc_cursor_t or
       mongoc_change_stream_t using a session must be destroyed before  the  session,  and  a  session  must  be
       destroyed before the mongoc_client_t it came from.

       By  default,  sessions  are causally consistent. To disable causal consistency, before starting a session
       create       a       mongoc_session_opt_t       with       mongoc_session_opts_new()       and       call
       mongoc_session_opts_set_causal_consistency(), then free the struct with mongoc_session_opts_destroy.

       Unacknowledged writes are prohibited with sessions.

       A  mongoc_client_session_t  must  be  used  by  only  one  thread  at  a  time.  Due  to session pooling,
       mongoc_client_start_session may return a session that has been idle for some time  and  is  about  to  be
       closed  after  its idle timeout. Use the session within one minute of acquiring it to refresh the session
       and avoid a timeout.

EXAMPLE

       example-session.c

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

          /* ./example-session [CONNECTION_STRING] */

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

          int
          main (int argc, char *argv[])
          {
             int exit_code = EXIT_FAILURE;

             mongoc_client_t *client = NULL;
             const char *uri_string = "mongodb://127.0.0.1/?appname=session-example";
             mongoc_uri_t *uri = NULL;
             mongoc_client_session_t *client_session = NULL;
             mongoc_collection_t *collection = NULL;
             bson_error_t error;
             bson_t *selector = NULL;
             bson_t *update = NULL;
             bson_t *update_opts = NULL;
             bson_t *find_opts = NULL;
             mongoc_read_prefs_t *secondary = NULL;
             mongoc_cursor_t *cursor = NULL;
             const bson_t *doc;
             char *str;
             bool r;

             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);
                goto done;
             }

             client = mongoc_client_new_from_uri (uri);
             if (!client) {
                goto done;
             }

             mongoc_client_set_error_api (client, 2);

             /* pass NULL for options - by default the session is causally consistent */
             client_session = mongoc_client_start_session (client, NULL, &error);
             if (!client_session) {
                fprintf (stderr, "Failed to start session: %s\n", error.message);
                goto done;
             }

             collection = mongoc_client_get_collection (client, "test", "collection");
             selector = BCON_NEW ("_id", BCON_INT32 (1));
             update = BCON_NEW ("$inc", "{", "x", BCON_INT32 (1), "}");
             update_opts = bson_new ();
             if (!mongoc_client_session_append (client_session, update_opts, &error)) {
                fprintf (stderr, "Could not add session to opts: %s\n", error.message);
                goto done;
             }

             r = mongoc_collection_update_one (
                collection, selector, update, update_opts, NULL /* reply */, &error);

             if (!r) {
                fprintf (stderr, "Update failed: %s\n", error.message);
                goto done;
             }

             bson_destroy (selector);
             selector = BCON_NEW ("_id", BCON_INT32 (1));
             secondary = mongoc_read_prefs_new (MONGOC_READ_SECONDARY);

             find_opts = BCON_NEW ("maxTimeMS", BCON_INT32 (2000));
             if (!mongoc_client_session_append (client_session, find_opts, &error)) {
                fprintf (stderr, "Could not add session to opts: %s\n", error.message);
                goto done;
             };

             /* read from secondary. since we're in a causally consistent session, the
              * data is guaranteed to reflect the update we did on the primary. the query
              * blocks waiting for the secondary to catch up, if necessary, or times out
              * and fails after 2000 ms.
              */
             cursor = mongoc_collection_find_with_opts (
                collection, selector, find_opts, secondary);

             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);
                goto done;
             }

             exit_code = EXIT_SUCCESS;

          done:
             if (find_opts) {
                bson_destroy (find_opts);
             }
             if (update) {
                bson_destroy (update);
             }
             if (selector) {
                bson_destroy (selector);
             }
             if (update_opts) {
                bson_destroy (update_opts);
             }
             if (secondary) {
                mongoc_read_prefs_destroy (secondary);
             }
             /* destroy cursor, collection, session before the client they came from */
             if (cursor) {
                mongoc_cursor_destroy (cursor);
             }
             if (collection) {
                mongoc_collection_destroy (collection);
             }
             if (client_session) {
                mongoc_client_session_destroy (client_session);
             }
             if (uri) {
                mongoc_uri_destroy (uri);
             }
             if (client) {
                mongoc_client_destroy (client);
             }

             mongoc_cleanup ();

             return exit_code;
          }

AUTHOR

       MongoDB, Inc

COPYRIGHT

       2017-present, MongoDB, Inc

1.21.0                                            Feb 09, 2022                        MONGOC_CLIENT_SESSION_T(3)