serve/app/admin/library/crud/stubs/mixins/model/afterInsert.stub

    protected static function onAfterInsert($model)
    {
        if ($model->{%field%} == 0) {
            $pk = $model->getPk();
            if (strlen($model[$pk]) >= 19) {
                $model->where($pk, $model[$pk])->update(['{%field%}' => $model->count()]);
            } else {
                $model->where($pk, $model[$pk])->update(['{%field%}' => $model[$pk]]);
            }
        }
    }