Utility method: rename columns in an index definition according to a new mapping.
$key_definition: The key definition.
$mapping: The new mapping.
protected function mapKeyDefinition(array $key_definition, array $mapping) {
foreach ($key_definition as &$field) {
// The key definition can be an array($field, $length).
if (is_array($field)) {
$field =& $field[0];
}
if (isset($mapping[$field])) {
$field = $mapping[$field];
}
}
return $key_definition;
}