LazyRecord\Schema\Relationship\Relationship::where PHP Method

    public function where($expr = null, array $args = array())
    {
        if (!$this->where) {
            $this->where = new Conditions();
        }
        if ($expr) {
            if (is_string($expr)) {
                $this->where->appendExpr($expr, $args);
            } elseif (is_array($expr)) {
                foreach ($expr as $key => $val) {
                    $this->where->equal($key, $val);
                }
            } else {
                throw new InvalidArgumentException("Unsupported argument type of 'where' method.");
            }
        }
        return $this->where;
    }