[英]How to set up and access class properties in Node.js?
我無法訪問我創建的對象中的數據。 我是JS和節點的新手,我認為我的問題是我如何初始化變量,但我不知道。
這是我的初始化:
var http = require('http');
var MongoClient = require('mongodb').MongoClient;
var async = require('async');
var currentBoatList = [];
var BoatObjectList = [];
我有一個班級來創建船的當前信息(取自數據庫):
function CurrentBoatInfo(boatName) {
var name,MMSI,callSign,currentDate,positionJSON,status,speed,course;
database.collection('Vessels').find({"BoatName":boatName},{"sort":{DateTime:-1}}).toArray(function(error1,vessel) {
name = vessel[0].BoatName;
MMSI = vessel[0].MMSI;
callSign = vessel[0].VesselCallSign;
console.log(name); \\logs the boats name, so the variable is there
});
});
}
我有我的數據庫功能,它可以提取最近的船只,將它們的名字放在一個列表中,然后在另一個列表中為列表中的每個船名創建對象:
編輯:我看到我多次不必要地連接到mongoDB,使用代碼來修復它,並清除'db'變量名。
var createBoats = function() {
MongoClient.connect('mongodb://localhost:27017/tracks', function(err,database){
if (err) {return console.dir(err); }
else {console.log("connect to db");}
database.collection('Vessels').find({"MostRecentContact": { "$gte": (new Date((new Date()).getTime() - (365*24*60*60*1000)))}}).toArray(function(error,docs) { //within a year
docs.forEach(function(entry, index, array) {
currentBoatList.push(entry.BoatName); //create list of boats
BoatObjectList.push(new CurrentBoatInfo(entry.BoatName,database));
});
server();
});
});
};
最后我的服務器代碼只是創建一個服務器,並且應該記錄上面創建的每個對象的一些信息,但由於某種原因沒有(在下面輸出):
var server = function() {
http.createServer(function handler(req, res) {
res.writeHead(200, {'Content-Type': 'text/plain'});
console.log(BoatObjectList); //array of CurrentBoatInfo objects, prints [CurrentBoatInfo {}, CurrentBoatInfo {}, CurrentBoatInfo {}]
console.log(BoatObjectList[0].name); //prints undefined
BoatObjectList.forEach(function(entry) {
var count = 0;
for(var propertyName in entry.CurrentBoatInfo) { //nothing from here prints
console.log(JSON.stringify(propertyName));
count++;
console.log(count);
}
});
res.end();
}).listen(1337, '127.0.0.1');
};
我看到的輸出是這樣的:
connect to db
[ 'DOCK HOLIDAY', 'BOATY MCBOATFACE', 'PIER PRESSURE' ] //list of boats
DOCK HOLIDAY //boat names as they're being instantiated
BOATY MCBOATFACE
PIER PRESSURE
[ CurrentBoatInfo {}, CurrentBoatInfo {}, CurrentBoatInfo {} ] //list of boat objects
undefined //the name of the first boat in the object list
[ CurrentBoatInfo {}, CurrentBoatInfo {}, CurrentBoatInfo {} ]
undefined
考慮到這一點,我現在認為我的問題是createServer代碼運行,但不記錄,然后當我訪問127.0.0.1:1337時,它記錄名稱(實例化時未定義)...但是怎么做我讓createServer等待實例化對象?
我能發現的一個明顯問題是這段代碼:
docs.forEach(function(entry, index, array) {
currentBoatList.push(entry.BoatName); //create list of boats
if (currentBoatList.length === array.length) {
console.log(currentBoatList);
async.eachOf(currentBoatList, function(entry,index,array) {
BoatObjectList[index] = new CurrentBoatInfo(currentBoatList[index]); //create object of the boat's info
}, server()); //create the server after creating the objects
}
});
這里的問題是async.eachOf是在同步docs.forEach函數內運行的異步函數。 此外, async.eachOf的第二個參數應該有一個必須為數組中的每個項調用的回調,如:
async.eachOf(array, function(item, index, callback) {
doSomethingAsync(function(err, result) {
if (err) return callback(err);
// do something with result
callback();
});
}, function(err) {
// this is called when all items of the array are processed
// or if any of them had error, err here will contain the error
if(err) {
console.log("something went wrong", err);
} else {
console.log("success");
}
});
正如您所看到的那樣,運行server()作為回調看起來不正確,因為您應該確保沒有錯誤首先傳遞給最終回調然后繼續。
對於你的情況,我不明白為什么你使用async.eachOf而不是簡單的currentBoatList.forEach,因為你沒有在循環中做任何異步操作,你只是填充BoatObjectList。
UPD您的問題是您在假設變量准備好之前不等待異步操作完成。 我希望以下內容能讓您了解如何實現所需(注意我已經重命名了一些變量和函數,以使它們更清晰易懂):
database.collection('Vessels').find(query).toArray(function(err, vessels) {
if (err) {
// process error
return;
}
async.eachOf(vessels, function(vessel, index, next) {
currentBoatList.push(vessel.BoatName);
getVesselInfoByName(vessel.BoatName, function(err, info) {
if (err) {
return next(err);
}
vesselsInfoList.push(info);
next();
});
}, function(err) {
if (err) {
// process error
return;
}
// all vessels are processed without errors, vesselsInfoList is ready to be used
server();
});
});
function getVesselInfoByName(vesselName, callback) {
// do everything you need to get vessel info
// once you have received the vesselInfo call callback
// if any error happens return callback(err);
// otherwise return callback(null, vesselInfo);
}
一般來說,我建議您了解有關node.js asyncronius函數如何工作的更多信息,然后仔細查看異步庫文檔。
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