Question

这是我的NodeJS代码，我想在执行查询后返回csvFile数组，但我首先返回一个空数组，然后执行查询。我在getSummary函数中调用getDetection函数。这两个函数都在执行查询。有人可以帮帮我吗？

function getSummary(req, res) {
  var result = [];
  var csvFile = new Array();
  //console.log(csvFile);
  pool.getConnection(function(err, connection){
    if (err) {
          res.json({"code" : 100, "status" : "Error in connection database"});
          return;
        } 
    //var result = [];
    var option = req.body;
    //console.log(option.type);
    connection.query("SELECT DISTINCT name FROM dgh WHERE name LIKE ? ", ['%' + option.type.toUpperCase() + '%'], 
      function(err, rows, fields) {

        connection.release();
         if (err) {
          throw err;
        } else {
          for (var i = 0; i < rows.length; i++) {
           var row = rows[i].name;
           result.push(row);
           getDetection(result[i], function(result) {
            if (err) {
              throw err;
            } else {
            var count = result.count;
            var maxD = result.maxD;
            var array = new Array(count, maxD);
            csvFile.push(array); 
            //console.log(csvFile);
            }
           });
          }
        } 
    });  
  })

  console.log(csvFile);
  res.csv(csvFile);
}

getDetection函数：

function getDetection(filename, callback) {
    pool.getConnection(function(err, connection){
    if (err) {
          res.json({"code" : 100, "status" : "Error in connection database"});
          return;
        }   
    connection.query("SELECT hour, minute, second FROM dgh WHERE name = ?", [filename], 
      function(err, rows, fields){
        connection.release();
        if (err) {
          throw err;
        } else {
          var count = 0;
          var maxD = 0;
          for (var i = 1; i < rows.length; i++) {
            var time1 = rows[i].hour * 3600 + rows[i].minute * 60 + rows[i].second;
            var time2 = rows[i - 1].hour * 3600 + rows[i - 1].minute * 60 + rows[i].second;
            if (time2 - time1 > 60) {
              count = count + 1;
              maxD = Math.max(maxD, time2 - time1);
            }
          }
          callback({count:count, maxD:maxD});
        }

    })

  })
}

Answer 1

Node.js是异步的。如果 getDetection 是循环的异步函数，则不会按预期执行。

for (var i = 0; i < rows.length; i++) {
       var row = rows[i].name;
       result.push(row);
       getDetection(result[i], function(result) {
            if (err) {
               throw err;
            } else {
                var count = result.count;
                var maxD = result.maxD;
                var array = new Array(count, maxD);
                csvFile.push(array); 
                //console.log(csvFile);
            }
       })
    }
}

截至目前，for循环只会通过 getDetection 函数并完成迭代。这会导致变量 csvFile 为空。

我建议您使用 npm 安装 async 包。

npm install --save async

安装后

async.each(rows, function(name, callback) {
    result.push(name)
    getDetection(name, function(item){
        if (err) throw err

        var count = item.count
        var maxD = item.maxD
        var array = new Array(count, maxD)
        csvFile.push(array)
        callback()
    })
}, function(err){
    if (err) {
        //Handle error here that occurred during iteration
    } else { //finished all iteration
        console.log(csvFile)
        res.csv(csvFile)
        return 
    }
})

在MySQL查询执行之前已发送NodeJS响应

1 个答案: