Creating indexes

This example will show how to properly create indexes, how to verify its success, and will also give hints on how to prepare the BSON used to create the index.

#include <mongo.h>

#include <errno.h>
#include <stdio.h>

We will be creating and verifying multiple indexes, so lets create a function that takes a connection, a prepared index, and does the create and verify magic.

static void
create_and_verify_index(mongo_sync_connection *conn,
                        bson *index)
{
  if (!mongo_sync_cmd_index_create (conn, "lmc.indexed", index,
                                    MONGO_INDEX_UNIQUE | MONGO_INDEX_DROP_DUPS |
                                    MONGO_INDEX_SPARSE))
    {
      gchar *error = NULL;
      int e = errno;

      mongo_sync_cmd_get_last_error (conn, "lmc.indexed", &error);
      fprintf (stderr, "Can't create indexes: %s\n", error ? error : strerror (e));
      g_free (error);
    }
  else
    printf ("Index successfully created!\n");
}

This will create the index, and if it succeeds, write that to stdout. If it fails, it will try to query the last error, and print that to stderr.

All we have to do past this point, is to build a few index specifications in BSON, and see what happens:

int
main (void)
{
  mongo_sync_connection *conn;
  bson *invalid_index, *index;

  invalid_index = bson_build (BSON_TYPE_STRING, "name", "", -1,
                              BSON_TYPE_NONE);
  bson_finish (invalid_index);

The first index spec we create will have a single index field, name, where we set the value to an empty string. However - as we will soon see - this is not a valid specification, as MongoDB does not accept string-typed fields in the index spec.

  index = bson_build (BSON_TYPE_INT32, "name", 1,
                      BSON_TYPE_NONE);
  bson_finish (index);

Armed with the knowledge that strings are not going to work, we turn to our trusty old integers. Integers (32-bit integers at that, there really is no need to use a 64-bit value here) are the best fit for the type of an index field, because one can tell MongoDB the sort order (with negative or positive numbers) with them easily.

  conn = mongo_sync_connect ("localhost", 27017, FALSE);
  if (!conn)
    {
      fprintf (stderr, "Connection failed: %s\n", strerror (errno));
      return 1;
    }

We now have two index specs in BSON, and an established connection, lets see what happens!

  create_and_verify_index (conn, invalid_index);
  create_and_verify_index (conn, index);

The first will - as explained above - fail, the second will succeed.

And that is all it takes to create simple indexes! We now free up our BSON objects and disconnect, and the tutorial program is all done and finished.

  bson_free (invalid_index);
  bson_free (index);
  mongo_sync_disconnect (conn);

  return 0;
}