node.js 中的 javascript 代码和 rethinkdb 作为后端有什么问题？

Question

我的javascript代码如下：

var r = require('rethinkdb');

var soll1=null; 
var soll=null; 
r.connect( {host: 'localhost', port: 28015}, function(err, conn) {

r.db("discogs").table("releases").limit(4).run(conn, function(err, cursor) {
if (err) throw err;
    cursor.toArray(function(err, result) {
    if (err) throw err;

    soll=result.country;
});

});
});

  var http = require('http');
   http.createServer(function (req, res)    {res.write(soll);res.end();}).listen(3001, "127.0.0.1");
 console.log('Server running at http://127.0.0.1:3001/');

我在rethinkdb中的JSON如下。我想提取 "country" 值：

    {
    "release":{
       "genres":{
         "genre":"Electronic"
      },
  "identifiers":{
     "identifier":[
        {
           "description":"A-Side",
           "value":"MPO SK 032 A1 G PHRUPMASTERGENERAL T27 LONDON",
           "type":"Matrix / Runout"
        },
        {
           "description":"B-Side",
           "value":"MPO SK 032 B1",
           "type":"Matrix / Runout"
        },
        {
           "description":"C-Side",
           "value":"MPO SK 032 C1",
           "type":"Matrix / Runout"
        },
        {
           "description":"D-Side",
           "value":"MPO SK 032 D1",
           "type":"Matrix / Runout"
        }
     ]
  },
  "status":"Accepted",
  "videos":{
     "video":[
        {
           "title":"The Persuader (Jesper Dahlbäck) - Östermalm",
           "duration":290,
           "description":"The Persuader (Jesper Dahlbäck) - Östermalm",
           "src":"http://www.youtube.com/watch?v=AHuQWcylaU4",
           "embed":true
        },
        {
           "title":"The Persuader - Vasastaden",
           "duration":380,
           "description":"The Persuader - Vasastaden",
           "src":"http://www.youtube.com/watch?v=5rA8CTKKEP4",
           "embed":true
        },
        {
           "title":"The Persuader-Stockholm-Sodermalm",
           "duration":335,
           "description":"The Persuader-Stockholm-Sodermalm",
           "src":"http://www.youtube.com/watch?v=QVdDhOnoR8k",
           "embed":true
        },
        {
           "title":"The Persuader - Norrmalm",
           "duration":289,
           "description":"The Persuader - Norrmalm",
           "src":"http://www.youtube.com/watch?v=hy47qgyJeG0",
           "embed":true
        }
     ]
  },
  "labels":{
     "label":{
        "catno":"SK032",
        "name":"Svek"
     }
  },
  "companies":{
     "company":[
        {
           "id":271046,
           "catno":"",
           "name":"The Globe Studios",
           "entity_type_name":"Recorded At",
           "resource_url":"http://api.discogs.com/labels/271046",
           "entity_type":23
        },
        {
           "id":56025,
           "catno":"",
           "name":"MPO",
           "entity_type_name":"Pressed By",
           "resource_url":"http://api.discogs.com/labels/56025",
           "entity_type":17
        }
     ]
  },
  "styles":{
     "style":"Deep House"
  },
  "formats":{
     "format":{
        "text":"",
        "name":"Vinyl",
        "qty":2,
        "descriptions":{
           "description":[
              "12\"",
              "33 ⅓ RPM"
           ]
        }
     }
  },
  "country":"Sweden",
  "id":1,
  "released":"1999-03-00",
  "artists":{
     "artist":{
        "id":1,
        "anv":"",
        "name":"Persuader, The",
        "role":"",
        "tracks":"",
        "join":""
     }
  },
  "title":"Stockholm",
  "master_id":5427,
  "tracklist":{
     "track":[
        {
           "position":"A",
           "duration":"4:45",
           "title":"Östermalm"
        },
        {
           "position":"B1",
           "duration":"6:11",
           "title":"Vasastaden"
        },
        {
           "position":"B2",
           "duration":"2:49",
           "title":"Kungsholmen"
        },
        {
           "position":"C1",
           "duration":"5:38",
           "title":"Södermalm"
        },
        {
           "position":"C2",
           "duration":"4:52",
           "title":"Norrmalm"
        },
        {
           "position":"D",
           "duration":"5:16",
           "title":"Gamla Stan"
        }
     ]
  },
  "data_quality":"Complete and Correct",
  "extraartists":{
     "artist":{
        "id":239,
        "anv":"",
        "name":"Jesper Dahlbäck",
        "role":"Music By [All Tracks By]",
        "tracks":"",
        "join":""
     }
  },
  "notes":"The song titles are the names of Stockholm's districts."
   }
 }

当我尝试使用 node.js 运行时，出现以下错误：

 http.js:852
     throw new TypeError('first argument must be a string or Buffer');
      ^
 TypeError: first argument must be a string or Buffer
     at ServerResponse.OutgoingMessage.write (http.js:852:11)
    at Server.<anonymous> (/home/dhiraj/http_server.js:19:44)
at Server.emit (events.js:98:17)
at HTTPParser.parser.onIncoming (http.js:2109:12)
at HTTPParser.parserOnHeadersComplete [as onHeadersComplete] (http.js:122:23)
at Socket.socket.ondata (http.js:1967:22)
at TCP.onread (net.js:528:27)

抱歉，如果我的问题看起来很麻烦。但是我不明白我哪里错了？

Answer 1

如错误消息所述，res.write 需要字符串或 Buffer 对象，因此您必须确保输出为字符串。

soll=result.country;

您在某些 callback 函数中设置了 soll 变量，与 res.write(soll); 语句相比，这些函数将在稍后的时间点执行。

所以为了调试目的你可以试试

res.write(soll?soll:'soll has null value');

我希望你会看到

soll has null value

这样至少你能明白你的情况出了什么问题:D

希望这对您有所帮助:D

Answer 2

当您尝试发送时，变量 soll 很可能仍然为 null。放

console.log('soll:', soll);

就在 res.write...之前检查它。

node.js 中的 javascript 代码和 rethinkdb 作为后端有什么问题？

What is wrong with this javascript code in node.js and with rethinkdb as backend?

javascript

node.js

rethinkdb