mongoc_cursor_t

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:

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;
}

Functions