表达随机顺序调用的中间件函数

Question

我正在编写一条生成多张发票的路线。 我正在使用的中间件从 mysql 数据库中获取数据。 就是先检查custid是否存在，然后获取客户的季度成本，然后生成发票号。 我使用的代码如下：

中间件：

enter code here
const  check_exists=async(req,res,next)=>{

var sql='SELECT EXISTS(SELECT 1 FROM customers WHERE id ='
                                +req.query.custid+') AS ex;'
connection.query(sql, await function(err,result)  {
if(err) throw err;
    console.log('check_exists=='+result[0].ex)
    req.exist=result[0].ex
      if(result[0].ex<1){
        //res.send('custid '+req.query.custid+' no exist')
        res.end()
      }//{res.send('custid '+req.query.custid+' no exist')}
  else{  next() }
});////connection                                   

}



enter code here
const  getQcost=async(req,res,next)=>{
var sql='SELECT quarterly_cost from customers'+
        ' WHERE id='+req.query.custid+';'

connection.query(sql, await function(err,result)  {
if(err) throw err;
req.Qcost=result[0].quarterly_cost;
console.log('quarter_ cost=='+req.Qcost)
next()
});////connection           
}


enter code here
const inv_count=async(req,res,next)=>{
var sql='SELECT COUNT(custID) AS inv_count from payments '+
        ' where (custID='+req.query.custid+' && invoice_no!="");';
connection.query(sql, await function(err,result)  {
    if(err) throw err;
      //console.log('Data saved to payments:\n');
        //console.log('the variable result====',JSON.stringify(result));
        console.log('inv_count=='+result[0].inv_count)
        req.inv_count=result[0].inv_count;
        next()
});////connection

}

接电话：

enter code here
router.get('/inv',check_exists, getQcost, inv_count, function(req,res,next){
req.inv=(req.inv_count+1).toString()
req.invoice_no=req.query.custid+'-'+req.inv
var VALUES='('+req.query.custid+', CURDATE(), '+req.Qcost+
            ' , '+'"for regular cleans in quarter: 12 Apr 20-12 July 20"'+
            ', '+'"'+req.invoice_no+'"'+')'

res.send(VALUES)
})

它应该运行 check_exists 然后 getQcost 然后 inv_count。 但是，它在调用 3 次时给出的输出如下：

enter code here

check_exists==1
quarter_ cost==23.4
inv_count==1
check_exists==1
check_exists==1
quarter_ cost==23.4
quarter_ cost==23.4
inv_count==1
inv_count==1

我的代码有问题吗？ 对于少量的呼叫似乎无关紧要，但遇到麻烦时 调用次数超过200左右。

Answer 1

你犯的错误是，你混淆了await和callback的概念！这是修改后的代码，希望对你有用！

const check_exists=async(req,res,next)=>{
    var sql='SELECT EXISTS(SELECT 1 FROM customers WHERE id ='+req.query.custid+') AS ex;'
    try{
        const result=await connection.query(sql);

        console.log('check_exists=='+result[0].ex);
        req.exist=result[0].ex;

        if(result[0].ex<1){
            //res.send('custid '+req.query.custid+' no exist')
            res.end()
          }//{res.send('custid '+req.query.custid+' no exist')}
        else{  
            next(); 
        }
    }catch(err){
        throw err;
        //console.log(err);
    }
};

const getQcost=async(req,res,next)=>{
    var sql='SELECT quarterly_cost from customers'+' WHERE id='+req.query.custid+';'
    try{
        const result=await connection.query(sql);
        req.Qcost=result[0].quarterly_cost;
        console.log('quarter_ cost=='+req.Qcost);
        next();
    }catch(err){
        throw err;
        //console.log(err);
    }           
};

const inv_count=async(req,res,next)=>{
    var sql='SELECT COUNT(custID) AS inv_count from payments '+' where (custID='+req.query.custid+' && invoice_no!="");';
    try{
        const result=await connection.query(sql);
        //console.log('Data saved to payments:\n');
        //console.log('the variable result====',JSON.stringify(result));
        console.log('inv_count=='+result[0].inv_count);
        req.inv_count=result[0].inv_count;
        next();
    }catch(err){
        throw err;
        //console.log(err);
    }
};