SYNOPSIS

const bson_t *doc;
mongoc_cursor_t * cursor;

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

while (mongoc_cursor_next (cursor, &doc)) {
   do_something(doc);
}

DESCRIPTION

mongoc_cursor provides access to a MongoDB query cursor. It wraps up the wire protocol negotation required to initiate a query and retreive an unknown number of documents.

Cursors are lazy, meaning that no network traffic occurs until the first mongoc_cursor_next(3).

At that point we can:

THREAD SAFETY

mongoc_cursor is NOT thread-safe and should only be used from one thread at a time.

LIFECYCLE

The bson objects set in mongoc_cursor_next(3) are ephemeral and good until the next call. mongoc_cursor_destroy(3) must be called to clean up, even in the case of exhausted cursors.

EXAMPLE

The following example connects to a single MongoDB instance and performs a simple query against it. The resulting documents are printed as JSON to standard output.

/* 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_error (cursor, &error) &&
          mongoc_cursor_more (cursor)) {
      if (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);

   return EXIT_SUCCESS;
}

SEE ALSO

AUTHORS

This page was written by MongoDB Inc.