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MONGOC_CURSOR_T(3) libmongoc MONGOC_CURSOR_T(3)

Client-side cursor abstraction

SYNOPSIS

typedef struct _mongoc_cursor_t mongoc_cursor_t;


mongoc_cursor_t provides access to a MongoDB query cursor. It wraps up the wire protocol negotiation required to initiate a query and retrieve an unknown number of documents.

Common cursor operations include:

  • Determine which host we've connected to with mongoc_cursor_get_host().
  • Retrieve more records with repeated calls to mongoc_cursor_next().
  • Clone a query to repeat execution at a later point with mongoc_cursor_clone().
  • Test for errors with mongoc_cursor_error().

Cursors are lazy, meaning that no connection is established and no network traffic occurs until the first call to mongoc_cursor_next().

THREAD SAFETY

mongoc_cursor_t is NOT thread safe. It may only be used from within the thread in which it was created.

EXAMPLE

Query MongoDB and iterate results

/* gcc example-client.c -o example-client $(pkg-config --cflags --libs


 * libmongoc-1.0) */
/* ./example-client [CONNECTION_STRING [COLLECTION_NAME]] */
#include <mongoc/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 *collection_name = "test";


   bson_t query;


   char *str;


   const char *uri_string = "mongodb://127.0.0.1/?appname=client-example";


   mongoc_uri_t *uri;


   mongoc_init ();


   if (argc > 1) {


      uri_string = argv[1];


   }


   if (argc > 2) {


      collection_name = argv[2];


   }


   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);


   bson_init (&query);


   collection = mongoc_client_get_collection (client, "test", collection_name);


   cursor = mongoc_collection_find_with_opts (collection,


                                              &query,


                                              NULL,  /* additional options */


                                              NULL); /* read prefs, NULL for default */


   while (mongoc_cursor_next (cursor, &doc)) {


      str = bson_as_canonical_extended_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_uri_destroy (uri);


   mongoc_client_destroy (client);


   mongoc_cleanup ();


   return EXIT_SUCCESS;
}


AUTHOR

MongoDB, Inc

COPYRIGHT

2009-present, MongoDB, Inc.

October 9, 2024 1.28.1