Node.js和MongoDb中的同步应用程序的结构

您可以根据需要扩展此示例.您可以创建函数createCollection const createCollection = (connection, collectionName) => { return connection.createCollection(collectionName); // actually i'm not sure that this function exists in mongodb driver}用法为:const mongodbLib = require('./lib/mongodb'); //path to db.js filemongodbLib.init() .then(connection => mongodbLib.createCollection(connection, 'cas')) .then(() => doSmthElse())或者如果您确定初始化已完成(可以在启动服务器之类的主脚本之前执行一次操作)const mongodbLib = require('./lib/mongodb'); //path to db.js fileconst connection = mongodbLib.getConnection();或者，如果您想像第6步那样简单地使用集合，请添加cas集合(例如示例文件中的用户).但这也可以在完成init函数时使用.因此用法将是const mongodbLib = require('./lib/mongodb');const cas = mongodbLib.collections.cas;cas().insertMany(docs) .then() .catch()I need to build an application that does these things (in order):on load: 01- connect to MongoDB 'db' 02- creates a collection 'cas' 03- check if a web page has updates, if yes go to step 04, if not go to step 07 04- do web scraping (using Cheerio) of the web site and get a $ variable like that $ = cheerio.load(body); 05- elaborate this object to get only informations I'm interested in and organize them in a jsons object like this one: var jsons = [ {year: 2015, country: Germany, value: 51}, {year: 2015, country: Austria, value: 12}, {year: 2016, country: Germany, value: 84}, {year: 2016, country: Bulgaria, value: 104}, ... ]; 06- insert each of these elements ({year: 2015, country: Germany, value: 51}, ...) in the collection 'cas' of database 'db' 07- download the data (for example in a csv file) 08- create a web page for data visualization of these data using D3.js 09- disconnect from 'db'If Node.js were synchronous, I could write something like this:var url = 'http://...';var jsons = [];connectDb('db');createCollection('db', 'cas');if(checkForUpdates(url)) { var $ = scrape(url); jsons = elaborate($); for(var i = 0; i < jsons.length; i++) { saveDocumentOnDbIfNotExistsYet('db', 'cas', jsons[i]); }}downloadCollectionToFile('db', 'cas', './output/casData.csv');createBarChart('./output/casData.csv');disconnectDb('db');But Node.js is asynchronous so this code would not work properly.I've read that I can use Promise to get the code to run in a certain order.I read the documentation about the Promise and some sites that showed simple tutorials.The structure of a Promise is:// some code (A)var promise = new Promise(function(resolve, reject) { // some code (B)});promise.then(function() { // some code (C)});promise.catch(function() { // some code (D)});// some code (E)If I understood correctly, in this case the execution (if Node.js were synchronous) would be equivalent to:// some code (A)// some code (E)if(some code (B) not produce errors) { // some code (C)}else { // some code (D)}or (swap between code A and E, because they are asynchronous)// some code (E)// some code (A)if(some code (B) not produce errors) { // some code (C)}else { // some code (D)}So now I wonder what is the right structure for my application.I thought about:var cheerio = require('cheerio');var express = require('express');var fs = require('fs');var MongoClient = require('mongodb').MongoClient;var dbUrl = 'mongodb://localhost:27017/';var dbName = 'db';var collectionName = 'cas';const app = express(); // run using > node app.js// connect to dbvar connect = function(url) { return new Promise(function(resolve, reject) { MongoClient.connect(url + dbName, function(err, db) { if(err) { reject(err); } else { console.log('Connected'); resolve(db); } }); });}// create collectionconnect.then(function(db) { db.createCollection(collectionName, function(err, res) { if(err) { throw err; } else { console.log('Collection', collectionName, 'created!'); } });});// connection errorconnect.catch(function(err) { console.log('Error during connection...'); throw err;});It's right? If yes, how can I proceed with other steps?I can I improve my code?EDIT 1Following the example of Андрей Щербаков, I modified my code in this way:app.js: // my filesvar db = require('./middlewares/db.js');var url = 'mongodb://localhost:27017/';var dbName = 'db';var collectionName = 'cas';const start = async function() { const connect = await db.connectToMongoDb(url, dbName); const cas = await connect.createYourCollection(collectionName); const isPageHasUpdates = oneMoreFunction(); // i don't know how you gonna check it if(isPageHasUpdates) { await step 4; await step 5; await step 6; } await step 7 return something; // if you want}start().then(res => console.log(res)) // here you can use result of your start function if you return something or skip this then.catch(err => console.log(err)); // do something with your errormiddlewares/db.js:var MongoClient = require('mongodb').MongoClient;let dbInstance;var methods = {};methods.connectToMongoDb = function(url, dbName) { if(dbInstance) { return dbInstance; } else { MongoClient.connect(url + dbName, function(err, db) { if(!err) { dbInstance = db; return db; } }); }}methods.createYourCollection = function(collectionName) { ?.createCollection(collectionName, function(err, res) { if(err) { throw err; } });}module.exports = methods;But I'm not sure I'm doing well.How can I separate function in different files? For example I want to put all the function about db in file middlewares/db.js. But I have some problems in line ?.createCollection(collectionName, function(err, res). 解决方案 If you are running node version 7.6 or higher, better way will be to use async await which works with promises.So your code will look like const start = async() => { const connect = await connectToMongoDb(url); const cas = await connect.createYourCollection(); const isPageHasUpdates = oneMoreFunction(); // i don't know how you gonna check it if(isPageHasUpdates) { await step 4; await step 5; await step 6; } await step 7 return something; // if you want}start().then(res => console.log(res)) // here you can use result of your start function if you return something or skip this then.catch(err => console.log(err)); // do something with your errorSure any function you are gonna await should be promisified as you did with your connect function( but if you are using https://www.npmjs.com/package/mongodb functions already promisified)UpdateThe best way will be to use mongoose, but if you want to work with native mongodb you can write your mongodb like this https://pastebin.com/BHHc0uVN (just an example)You can expand this example as you want.You can create function createCollectionconst createCollection = (connection, collectionName) => { return connection.createCollection(collectionName); // actually i'm not sure that this function exists in mongodb driver}And usage will be: const mongodbLib = require('./lib/mongodb'); //path to db.js filemongodbLib.init() .then(connection => mongodbLib.createCollection(connection, 'cas')) .then(() => doSmthElse())Or if you are sure that init is done(you can do it once before you main script like starting server or whatever you doing)const mongodbLib = require('./lib/mongodb'); //path to db.js fileconst connection = mongodbLib.getConnection();Or if you want to simple work with collection like in step 6, add your cas collection(like user in example file). But this you can use when your init function is done as well.So usage will beconst mongodbLib = require('./lib/mongodb');const cas = mongodbLib.collections.cas;cas().insertMany(docs) .then() .catch() 这篇关于Node.js和MongoDb中的同步应用程序的结构的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！ 上岸，阿里云！