Programmatic node creation, Drupal 6 and the drupal_get_schema() function

While working on importing a bunch of content from an old Drupal site to a new one, I discovered a little gotcha with the D6 database schema functionality. The method I was using involved loading a bunch of nodes from the old database via a call to db_set_active(), followed by a series of calls to node_load(). Once I had the nodes in an array, I switch to the new db via another call to db_set_active and store the nodes via node_save().

The problem arose due to the fact that Drupal is caching database schema information. Thus, during the node load phase, CCK attempts to load up information on a table that doesn't exist, and the result is cached. When back in the new database, where the table really does exist, the cached schema thinks it doesn't.

The solution was to clear the database schema cache every time I switched back to a different database:

function import_old_set_db($db = 'default') {
  db_set_active($db);
 
  // clear schema
  drupal_get_schema(NULL, TRUE);
}

The key in the above function, which I used as a wrapper to db_set_active() in my import script, is the call to the drupal_get_schema() function, which clears the cached database schema information.

This was a viable solution because this is a one-time import script where performance really isn't an issue. It would not be recommended for production sites when regularly switching between databases during normal page loads.