Converts a dict of RDF values into a SQL-ready form.

def _ConvertToCanonicalSqlDict(self, schema, raw_dict, prefix=""):
    """Converts a dict of RDF values into a SQL-ready form."""
    flattened_dict = {}
    for k, v in iteritems(raw_dict):
      if isinstance(v, dict):
        flattened_dict.update(
            self._ConvertToCanonicalSqlDict(
                schema, v, prefix="%s%s." % (prefix, k)))
      else:
        field_name = prefix + k
        flattened_dict[field_name] = schema[field_name].convert_fn(v)
    return flattened_dict