将 Mongoose 播种脚本变成承诺

Question

我正试图围绕承诺试图解决一个我经常发现自己的场景：播种 MongoDB 数据库。所以我得到了下面的脚本，我想把它变成一个 Promise，最好使用 ES6，但如果是这样的话，我会用蓝鸟作为答案。 这就是我在关闭数据库之前使用setTimeout 给写操作留出时间的结果：

// Importing the connection to the `bookshelf` db.
var bookshelfConn = require('./database');

// Importing the Mongoose model we'll use to write to the db.
var Book = require('./models/Book');

// Importing the Data to populate the db.
var books = require('./dataset');

// When the connection is ready, do the music!
bookshelfConn.on('open', function () {
  dropDb(seedDb, closeDb);
});

function dropDb (cb1, cb2) {
  bookshelfConn.db.dropDatabase();
  console.log('Database dropped!');
  cb1(cb2);
}

function seedDb (cb) {
  console.time('Seeding Time'); // Benchmarking the seed process.

  // Warning! Slow IO operation.
  books.forEach(function (book) {
    new Book(book).save(function (err) {
      if (err) console.log('Oopsie!', err);
    });
    console.log('Seeding:', book);
  });

  console.timeEnd('Seeding Time'); // Benchmarking the seed process.

  cb();
}

function closeDb () {
  setTimeout(function () {
    bookshelfConn.close(function () {
      console.log('Mongoose connection closed!');
    });
  }, 1000); // Delay closing connection to give enough time to seed!
}

更新代码以反映 zangw 的回答：

// Importing the connection to the `bookshelf` db.
var bookshelfConn = require('./database');

// Importing the Mongoose model we'll use to write to the db.
var Book = require('./models/Book');

// Importing the Data to populate the db.
var books = require('./dataset');

// When the connection is ready, do the music!
bookshelfConn.on('open', function () {
  // Here we'll keep an array of Promises
  var booksOps = [];

  // We drop the db as soon the connection is open
  bookshelfConn.db.dropDatabase(function () {
    console.log('Database dropped');
  });

  // Creating a Promise for each save operation
  books.forEach(function (book) {
    booksOps.push(saveBookAsync(book));
  });

  // Running all the promises sequentially, and THEN
  // closing the database.
  Promise.all(booksOps).then(function () {
    bookshelfConn.close(function () {
      console.log('Mongoose connection closed!');
    });
  });

  // This function returns a Promise.
  function saveBookAsync (book) {
    return new Promise(function (resolve, reject) {
      new Book(book).save(function (err) {
        if (err) reject(err);
        else resolve();
      });
    });
  }
});

Answer 1

请尝试通过new Promise和Promise.all进行操作

new Promise 创建一个新的承诺。传入的函数将接收函数 resolve 和 reject 作为其参数，可以调用这些函数来确定创建的 Promise 的命运。

Promise.all 在您想要等待多个承诺完成时很有用。

var bookOps = [];

books.forEach(function (book) {
    bookOps.push(saveBookAsync(book));
});

Promise.all(bookOps).then(function() {
   bookshelfConn.close(function () {
      console.log('Mongoose connection closed!');
    });
});

function saveBookAsync(book) {
    return new Promise(function(resolve, reject) {
        new Book(book).save(function(err) {
            if (err)
                reject(err);
            else
                resolve();
        })
    });
}