Node js / express application -在函数中调用函数

node js / express application - calling a function within a function

本文关键字：函数 调用 application js express Node      更新时间：2023-09-26

背景信息

我有一个节点/express应用程序，连接到Redis数据库查询值的列表。然后，对于返回数据中的每个值，我需要执行进一步的查询。

初始查询(redis "scan"命令)工作得很好，但是我尝试对初始结果集中的每个项进行HGETALL查询的行为不符合预期。

为了演示这个问题，我在第34行添加了一个console.log命令来打印当前扫描记录的值…然后我在HGETALL的回调函数中再次输出它(第36行)，但值不同。在我看来，它们应该是一样的……但我确信这是node.js工作方式的基本原理，我错过了。

 27 router.get('/', function(req, res, next) {
 28         redis.send_command("SCAN", [0,"MATCH", "emergency:*"], function(err, reply) {
 29                 if (reply) {
 30                         var retdata = [];
 31                         console.log('length is: ' + reply[1].length);
 32                         for (var i = 0; i < reply[1].length; i++) {
 33                                 var emergIP = reply[1][i];
 34                                 console.log('emergIP outside the call: ' + emergIP);
 35                                 redis.hgetall(emergIP, function (err, data) {
 36                                         console.log('emergIP inside the call: ' + emergIP);
 37                                         if (data) {             
 38                                                 var temp = emergIP.split(":");
 39                                                 var key = temp[1];
 40                                                 console.log('the key is: ' + key);
 41                                                 //retdata.push({key:data.callerid});
 42                                         }
 43                                 });
 44                         }//end for loop
 45                         res.send(JSON.stringify(retdata));
 46                 } //end if
 47                 else {  
 48                         //no emergency data defined yet
 49                         var retval = {"res":false, "msg":"no emergency data defined"};
 50                         res.send(JSON.stringify(retval));
 51                 
 52                 }             
 53         }); //end send_command
 54 });
 55

代码输出

length is: 8
emergIP outside the call: emergency:10.1
emergIP outside the call: emergency:10.2
emergIP outside the call: emergency:10.13
emergIP outside the call: emergency:10.14
emergIP outside the call: emergency:10.18.90
emergIP outside the call: emergency:10.19
emergIP outside the call: emergency:10.20
emergIP outside the call: emergency:10.244
GET /emergency/ 200 220.368 ms - 2
emergIP inside the call: emergency:10.244
the key is: 10.244
emergIP inside the call: emergency:10.244
the key is: 10.244
emergIP inside the call: emergency:10.244
the key is: 10.244
emergIP inside the call: emergency:10.244
the key is: 10.244
emergIP inside the call: emergency:10.244
the key is: 10.244
emergIP inside the call: emergency:10.244
the key is: 10.244
emergIP inside the call: emergency:10.244
the key is: 10.244
emergIP inside the call: emergency:10.244
the key is: 10.244

我认为问题是我期望send_command函数的回调顺序发生。换句话说，也许问题是我不应该在另一个函数调用中有一个函数调用?这是我的第一个节点应用程序…我边做边学。

如有任何建议，不胜感激。

使用async。你可以利用闭包和立即调用的函数:

// get all elements from redis
function getAll(emergIP, callback) {
  redis.hgetall(emergIP, function (err, data) {
    if (err) {
      return callback(err);
    }
    console.log('emergIP inside the call: ' + emergIP);
    if (data) {
      var temp = emergIP.split(":");
      var key = temp[1];
      console.log('the key is: ' + key);
    }
    return callback(null, data);
  });
}
// Iterate all over the results
function getResults (reply, callback) {
  var retdata = [];
  console.log('length is: ' + reply.length);
  var length = reply.length;
  if (!length) {
    return callback(null, retdata);
  }
  for (var i = 0; i < length; i++) {
    var emergIP = [i];
    console.log('emergIP outside the call: ' + emergIP);
    (function (emergIP, i) {
      getAll(emergIP, function (err, data) {
        if (err) {
          // @todo: how would you like to handle the error?
        }
        retdata.push({key:data.callerid});
        if (i === length - 1) {
          return callback(null, retdata);
        }
      });
    }(emergIP, i));
  } //end for loop
}
router.get('/', function (req, res, next) {
  redis.send_command("SCAN", [0, "MATCH", "emergency:*"], function (err, reply) {
    if (reply) {
      getResults(reply[1], function (err, data) {
        if (err) {
          // @todo: how would you like to handle this in case of error?
        }
        res.send(JSON.stringify(data));
      });
    } //end if
    else {
      //no emergency data defined yet
      var retval = { "res": false, "msg": "no emergency data defined" };
      res.send(JSON.stringify(retval));
    }
  }); //end send_command
});

编辑

我修改了一点代码，以便在迭代结束时返回json。这不是完美的代码，因为在这种情况下，如果没有要迭代的结果，它根本不会向客户端返回响应。考虑使用async。每个:http://caolan.github.io/async/docs.html . each

EDIT2

我已经尝试解耦代码并将其拆分为函数。您可以将这些函数移到另一个文件中，然后将它们放到路由器中。对不起，如果有任何错别字，不允许代码正常运行，我实际上并没有尝试运行它。

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