执行失败时如何处理Codeigniter查询异常

Question

如何在codeigniter中检查返回的查询是否正在运行

public function checkBranch($myData){
    $qResult= array();
    extract($myData);

    $this->db->select('*');
    $this->db->where('branch_name',$branch_name);
    $this->db->where('branch_city',$branch_city);
    //Here i want to execute else if query failed
    if($query = $this->db->get('branch')){

        $rowCount = $query->num_rows();
        if ($rowCount<=0) {

            //now check for is_main_branch status
            $this->db->select('*');
            $this->db->where_not_in('branch_name',$branch_name);
            $this->db->where('branch_city',$branch_city);
            $this->db->where('is_main_branch',"true");
            $query = $this->db->get('branch');
            $rowCount = $query->num_rows();
            if($rowCount>0){

                $qResult    = array(
                                    'q_status'  => 'true' ,
                                    'q_message' => "their is already a branch is set main for this city" 
                            );
            }
        }else if($rowCount==1){

            $qResult    = array(
                                'q_status'  => 'true' ,
                                'q_message' => "branch with city already exist in records" 
                            );
        }

    }else{

        $qResult    = array(
                            'q_status'  => 'true' ,
                            'q_message' => "inside else part" 
                        );
    }

    return $qResult;

}

每当我调用此方法时，都会为给定参数返回结果，但是当表中当时给定参数不可用时，它将在控制台中抛出此消息

<p>Severity: Notice</p>
<p>Message:  Undefined index: q_status</p>

所以我想在查询失败时执行else块，那么他们是否有任何一种方法可以检查查询是否执行，所以else块将执行