Question

我从查询中获取结果并将其存储在一个变量中，该变量将通过渲染发送，但是未给出错误变量的问题。请帮帮我。如果可能，请更正代码。

router.get('/create',(req,res)=>{

        connection.query('SELECT * FROM purchases',function(error,results,fields){

            var voucher = 'PH-'+results.length+1;
            connection.query('SELECT * FROM vendors where wid=?',[req.session.w_id],function(err,res,f){
                var vendors=res;
                connection.query('SELECT * FROM products where wid=?',[req.session.w_id],function(er,r,fi){
                    var products=r;


                })
            })

        });

        res.render('purchase_create',{voucher:voucher,vendors:vendors,products:products});  

});

错误是：未定义凭证

Answer 1

voucher仅在您传递给connection.query的回调函数中可用，与vendors和products相同。您必须将res.render调用移到最内层的函数中才能完成此工作：

router.get('/create', (req, res) => {
  connection.query('SELECT * FROM purchases', function (error, results, fields) {
    var voucher = 'PH-' + results.length + 1;
    connection.query('SELECT * FROM vendors where wid=?', [req.session.w_id], function (err, res, f) {
      var vendors = res;
      connection.query('SELECT * FROM products where wid=?', [req.session.w_id], function (er, r, fi) {
        var products = r;

        res.render('purchase_create', { voucher: voucher, vendors: vendors, products: products });
      });
    });
  });
});

Answer 2

连接对象的“查询”方法需要一个回调函数，该函数将在以下三个事件之一触发时执行：错误，字段，结果，这里分别用参数err，字段和行表示。

router.get('/create', (req, res) => {
  connection.query('SELECT * FROM purchases', function (error, results, fields) 
  {
    if (error) throw error;

    var voucher = 'PH-' + results.length + 1;
    connection.query('SELECT * FROM vendors where wid=?', [req.session.w_id], function (err, res, f) 
    {
         if (err) throw err;
         var vendors = res;
         connection.query('SELECT * FROM products where wid=?', [req.session.w_id], function (er, r, fi) 
         {
             if (er) throw er;
             var products = r;
             res.render('purchase_create', { voucher: voucher, vendors: vendors, products: products });
        });
     });
  });
});

无法访问在connection.query函数中声明的变量

2 个答案: