CI框架下开启事务的代码分析

<?php
// 开启事务,CI框架
$this->Systems_model->base_connect();
$this->Systems_model->db->initialize();
$this->Systems_model->db->trans_begin();
try {
    $rs = $this->Systems_model->Update($data, $condition, &#39;user&#39;, false);
    if (!$rs) {
        throw new Exception("用户信息修改失败");
    }
    if ($rs) {
        
        // 删除用户角色中间表中的对应ID数据 重新插入
        $delRes = $this->Systems_model->delete_user_role($id);
        if ($delRes) {
            foreach ($roles as $k => $v) {
                $roleData[&#39;iUserID&#39;] = $id;
                $roleData[&#39;sRoleID&#39;] = $v;
                $res = $this->Systems_model->Save($act, $roleData, &#39;user_role&#39;, false);
            }
        } else {
            throw new Exception("改变原有的角色失败");
        }
        if ($res) {
            if ($this->Systems_model->db->trans_status() === FALSE) {
                $this->Systems_model->db->trans_rollback();
            } else {
                $this->Systems_model->db->trans_commit();
            }
            getPower(true);// 修改成功后会更新登录者的用户权限
            $this->Systems_model->base_close();
            outPrintApiJson(0, &#39;修改成功&#39;);
        } else {
            throw new Exception("修改角色失败");
        }
    }
} catch (Exception $e) {
    $this->Systems_model->db->trans_rollback();
    $this->Systems_model->base_close();
    $msg = $e->getMessage();
    outPrintApiJson(1, $msg);
    exit;
}