lithium\data\source\Database::_fields PHP Method

    protected function _fields($fields, $context)
    {
        $alias = $context->alias();
        $models = $context->models($this);
        $list = array();
        foreach ($fields as $key => $field) {
            if (!is_string($field)) {
                if (isset($models[$key])) {
                    $field = array_fill_keys($field, true);
                    $list[$key] = isset($list[$key]) ? array_merge($list[$key], $field) : $field;
                } else {
                    $list[0][] = is_array($field) ? reset($field) : $field;
                }
                continue;
            }
            if (preg_match('/^([a-z0-9_-]+|\\*)$/i', $field)) {
                isset($models[$field]) ? $list[$field]['*'] = true : ($list[$alias][$field] = true);
            } elseif (preg_match('/^([a-z0-9_-]+)\\.(.*)$/i', $field, $matches)) {
                $list[$matches[1]][$matches[2]] = true;
            } else {
                $list[0][] = $field;
            }
        }
        return $list;
    }