void
mongoc_read_prefs_set_tags (mongoc_read_prefs_t *read_prefs,


                            const bson_t *tags);

#include <mongoc/mongoc.h>
static void
run_query_with_read_prefs_tags (mongoc_collection_t *collection)
{


   char *str;


   const bson_t *doc;


   bson_t filter = BSON_INITIALIZER;


   bson_error_t error;


   mongoc_cursor_t *cursor;


   mongoc_read_prefs_t *read_prefs;


   /*  Create a tagset representing


    *  [


    *    {"dc": "ny", "rack": "1" }, // Any node in rack1 in the ny datacenter


    *    {"dc": "ny", "rack": "2" }, // Any node in rack2 in the ny datacenter


    *    {"dc": "ny" },              // Any node in the ny datacenter


    *    {}                          // If all else fails, just any available node


    * ]


    */


   bson_t *tags = BCON_NEW (


      "0", "{", "dc", BCON_UTF8("ny"), "rack", BCON_UTF8("1"), "}",


      "1", "{", "dc", BCON_UTF8("ny"), "rack", BCON_UTF8("2"), "}",


      "2", "{", "dc", BCON_UTF8("ny"), "}",


      "3", "{", "}"


   );


   read_prefs = mongoc_read_prefs_new (MONGOC_READ_SECONDARY);


   mongoc_read_prefs_set_tags (read_prefs, tags);


   bson_destroy (tags);


   cursor =


      mongoc_collection_find_with_opts (collection, &filter, NULL, read_prefs);


   while (mongoc_cursor_next (cursor, &doc)) {


      str = bson_as_canonical_extended_json (doc, NULL);


      printf ("%s\n", str);


      bson_free (str);


   }


   if (mongoc_cursor_error (cursor, &error)) {


      fprintf (stderr, "Cursor error: %s\n", error.message);


   }


   mongoc_cursor_destroy (cursor);


   mongoc_read_prefs_destroy (read_prefs);


   bson_destroy (doc);
}
int main (void)
{


   mongoc_client_t *client;


   mongoc_collection_t *collection;


   mongoc_init ();


   client =


      mongoc_client_new ("mongodb://localhost/?appname=rp_tags&replicaSet=foo");


   mongoc_client_set_error_api (client, 2);


   collection = mongoc_client_get_collection (client, "dbname", "collname");


   run_query_with_read_prefs_tags (collection);


   mongoc_collection_destroy (collection);


   mongoc_client_destroy (client);


   mongoc_cleanup();
}