public function automap() {
        $map = array();

        // Shallow copy.
        $collectionfrom = $this->get_collection_from();
        $collectionto = $this->get_collection_to();

        // Find mappings.
        foreach ($collectionfrom as $keyfrom => $compfrom) {
            foreach ($collectionto as $keyto => $compto) {
                if ($compfrom->get('idnumber') == $compto->get('idnumber')) {
                    $map[$compfrom->get('id')] = $compto->get('id');
                    unset($collectionfrom[$keyfrom]);
                    unset($collectionto[$keyto]);
                    break;
                }
            }
        }

        $this->mappings = $map;
    }