express.js + mongoose：回退不正確的ID？

Question

我使用expressong.js與mongoose進行mongoDB訪問。如果有人輸入一個不存在的url（基於user_id），我嘗試執行回退。下面的代碼：

app.get('/track/:id', function(req, res) { 
var user_id = req.params.id; 
User.findById(user_id, function(err, user_) { 
    if (!err) { 
     res.render('track', { pins: user_.pins, layout: false }); 
    } else { 
     res.send("FAIL! " + err); 
    } 
}); 
}); 

訪問http://foo.bar/track/1234和1234當它不存在，它應該打印出來FAIL！如果ID存在，它應該得到它從數據庫中的內容（這實際上工作）。這就是我現在得到輸入不正確的ID（應用程序崩潰）時：

/home/node/node-service/releases/20110530081158/server.js:112 
      res.render('track', { pins: user_.pins, layout: false }); 
              ^
TypeError: Cannot read property 'pins' of null 
    at /home/node/node-service/releases/20110530081158/server.js:112:46 
    at /home/node/.node_libraries/.npm/mongoose/1.3.6/package/lib/mongoose/query.js:778:22 
    at [object Object].<anonymous> (/home/node/.node_libraries/.npm/mongoose/1.3.6/package/support/node-mongodb-native/lib/mongodb/collection.js:462:35) 
    at [object Object].emit (events.js:67:17) 
    at [object Object].<anonymous> (/home/node/.node_libraries/.npm/mongoose/1.3.6/package/support/node-mongodb-native/lib/mongodb/db.js:94:12) 
    at [object Object].emit (events.js:64:17) 
    at Socket.<anonymous> (/home/node/.node_libraries/.npm/mongoose/1.3.6/package/support/node-mongodb-native/lib/mongodb/connection.js:86:16) 
    at Socket.emit (events.js:64:17) 
    at Socket._onReadable (net.js:671:31) 
    at IOWatcher.onReadable [as callback] (net.js:177:10) 

Answer 1

沒有返回數據爲不存在的ID是正常的操作，而不是錯誤，所以err沒有被設置。

嘗試更改if (!err)至if (!err && user_)。

Answer 2

請嘗試關閉回調參數>

User.findById(user_id, function(user_, err) { 
    if (!err) { 
     res.render('track', { pins: user_.pins, layout: false }); 
    } else { 
     res.send("FAIL! " + err); 
    } 
});