Question

我是nodejs和mongodb的新手。有人可以向我解释以下代码的行为吗？

var express = require('express')
var app = express();
var MongoClient = require('mongodb').MongoClient
const assert = require('assert')
const mongourl = 'mongodb://localhost:27017/test'
var str=""

MongoClient.connect(mongourl, function(err, client){
    assert.equal(null, err);
    var db = client.db('test');
    var cursor = db.collection('projects.testproject.exampleChannel.germany.parameter').find();
    cursor.forEach(function(item){
      if(item!=null){
        str=str+JSON.stringify(item)
        console.log("1 "+str)
      }
    })
    client.close();
    console.log("2 "+str)
  })

我得到以下输出，但不明白，为什么输出1是我期望的，而输出2为空。

2
1 {“ _id”：“ 5e67960fd92ba91300f5d718”，“ basicInfo”：{“ projectName”：“ exampleProject”，“ salesChannel”：“ exampleChannel”，“ country”：“德国”}，“类别”：{“ pieceItems”：{ “ amount”：0}，“ weightItems”：{“ amount”：0}，“ lengthItems”：{“ amount”：0}，“ volumeItems”：{“ amount”：0}，“ weightCodedItems”：{“ amount “：0}，” lengthCodedItems“：{”数量“：0}，” volumeCodedItems“：{”数量“：0}，” priceCodedItems“：{”数量“：0}，” deposit＆containerItems“：{”数量“： 0}，“ ageRestrictedItems”：{“金额”：0}，“ prepaidItems”：{“金额”：0}，“ e-loadingItems”：{“金额”：0}，“ guranteeItems”：{“金额”： 0}，“ paperReadingItems”：{“ amount”：0}，“ technicalItems”：{“ amount”：0}，“ giftItems”：{“ amount”：0}，“ commonCustomerCardItems”：{“ amount”：0} ，“ payBackCardItems”：{“ amount”：0}，“ deutschlandCardItems”：{“ amount”：0}，“ serviceItems”：{“ amount”：0}}}

Answer 1

forEach具有回调函数，您无需等待循环完成。尝试这样的事情

const express = require("express");
const app = express();
const MongoClient = require("mongodb").MongoClient;
const assert = require("assert");
const mongourl = "mongodb://localhost:27017/test";
let str = "";

MongoClient.connect(mongourl, async function (err, client) {
  assert.equal(null, err);
  const db = client.db("test");
  const cursor = db.collection("projects.testproject.exampleChannel.germany.parameter").find();
  while (await cursor.hasNext()) {
    const item = await cursor.next();
    if (item != null) {
      str += JSON.stringify(item);
      console.log(`1 ${str}`);
    }
  }
  client.close();
  console.log(`2 ${str}`);
});

用mongodb中的数据填充字符串

1 个答案: