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.TH "MONGOC_CLIENT_SESSION_T" "3" "Jun 04, 2021" "1.17.6" "libmongoc"
.SH NAME
mongoc_client_session_t \- mongoc_client_session_t
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.sp
Use a session for a sequence of operations, optionally with causal consistency. See \fI\%the MongoDB Manual Entry for Causal Consistency\fP\&.
.SH SYNOPSIS
.sp
Start a session with \fBmongoc_client_start_session\fP, use the session for a sequence of operations and multi\-document transactions, then free it with \fBmongoc_client_session_destroy()\fP\&. Any \fBmongoc_cursor_t\fP or \fBmongoc_change_stream_t\fP using a session must be destroyed before the session, and a session must be destroyed before the \fBmongoc_client_t\fP it came from.
.sp
By default, sessions are \fI\%causally consistent\fP\&. To disable causal consistency, before starting a session create a \fBmongoc_session_opt_t\fP with \fBmongoc_session_opts_new()\fP and call \fBmongoc_session_opts_set_causal_consistency()\fP, then free the struct with \fBmongoc_session_opts_destroy\fP\&.
.sp
Unacknowledged writes are prohibited with sessions.
.sp
A \fBmongoc_client_session_t\fP must be used by only one thread at a time. Due to session pooling, \fBmongoc_client_start_session\fP 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.
.SH EXAMPLE
.sp
example\-session.c
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
/* gcc example\-session.c \-o example\-session \e
 *     $(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\en"
               "error message:       %s\en",
               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\en", 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\en", error.message);
      goto done;
   }

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

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

   /* read from secondary. since we\(aqre 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\en", str);
      bson_free (str);
   }

   if (mongoc_cursor_error (cursor, &error)) {
      fprintf (stderr, "Cursor Failure: %s\en", 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;
}

.ft P
.fi
.UNINDENT
.UNINDENT
.SH AUTHOR
MongoDB, Inc
.SH COPYRIGHT
2017-present, MongoDB, Inc
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