用 Koa 提供 Restful service 和查询 MongoDB 的例子

const path = require('path');

const Koa = require('koa');
const app = new Koa();
const compose = require('koa-compose');
const router = require('koa-router')();
const bodyParser = require('koa-bodyparser');
const static = require('koa-static');
const static_root = static(path.join(__dirname + "/../client/dist")); // Point to the root of web app

const MongoClient = require('mongodb').MongoClient;
const DB_CONN_STR = 'mongodb://localhost:27017/sample';

// Variable for storing query result
var result = null;

// ********************************** Koa part **********************************

// Error handler
const handler = async (ctx, next) => {
    try {
        await next();
    } catch (err) {
        ctx.response.status = err.statusCode || err.status || 500;
        ctx.response.type = 'html';
        ctx.response.body = '<h2>Something wrong, please contact administrator.</h2>';
        //    ctx.app.emit('error', err, ctx);
    }
};

// Logger
const logger = async (ctx, next) => {
    console.log(`${ctx.request.method} ${ctx.request.url}`);
    await next();
};

const middlewares = compose([handler, bodyParser(), router.routes(), logger, static_root]);
app.use(middlewares);

// ********************************** DB part **********************************

// Common function to connect mongoDB, and run the callback function
var runDb = function (callback) {
    MongoClient.connect(DB_CONN_STR, function (err, db) {
        if (err) {
            console.log("Error: ", err);
            db.close();
            process.exit(1);
        } else {
            callback(db);
            db.close();
        }
    });
}

// Data for insert
var data1 = [
    { "name": "AAA", "age": 1 },
    { "name": "BBB", "company": "Google Co." }
];

// Insert function, just for testing
var insertData = function (db) {
    db.collection("table1").insert(data1, function (err, result) {
        if (err) {
            console.log("Error: ", err);
            return;
        }
    });
}

// Query function
var queryData = function (db) {
    db.collection("table1").find({}).toArray(function (err, docs) {
        if (err) {
            console.log("Error: ", err);
        } else {
            result = docs;
        }
    });
}

// Call the db to insert data
runDb(insertData);

// ********************************** Controller part **********************************

// Redirect the root to Angular index.html
router.get('/', async (ctx, next) => {
    ctx.response.redirect('/index.html');
});

// Just an api for testing
router.get('/ui-api/hello/:name', async (ctx, next) => {
    // just for sample
    var name = ctx.params.name;
    ctx.response.body = `<h1>Hello, ${name}!</h1>`;
});

// Just an api for testing
router.get('/ui-api/data', async (ctx, next) => {
    runDb(queryData);
    ctx.response.type = 'json';
    //    ctx.set("Access-Control-Allow-Origin", "*");    // Disable cross origin
    ctx.response.body = result;
});

// ********************************** Startup part **********************************

let port = 80;
app.listen(port);
console.log('app started at port : ' + port);