如何使用bluebird宣传MongoDB本机Javascript驱动程序？

Question

我想将MongoDB本机JS驱动程序与bluebird promises一起使用.我Promise.promisifyAll()该如何在这个库上使用？

Answer 1

2.0分支文档包含更好的宣传指南https://github.com/petkaantonov/bluebird/blob/master/API.md#promisification

它实际上有mongodb示例,它更简单:

var Promise = require("bluebird");
var MongoDB = require("mongodb");
Promise.promisifyAll(MongoDB);

Answer 2

使用时Promise.promisifyAll(),如果必须实例化目标对象,则有助于识别目标原型.对于MongoDB JS驱动程序,标准模式是:

• Db使用MongoClient静态方法或Db构造函数获取对象
• 打电话Db#collection()来获取一个Collection对象.

因此,借用/sf/answers/1521341251/,您可以:

var Promise = require('bluebird');
var mongodb = require('mongodb');
var MongoClient = mongodb.MongoClient;
var Collection = mongodb.Collection;

Promise.promisifyAll(Collection.prototype);
Promise.promisifyAll(MongoClient);

现在你可以:

var client = MongoClient.connectAsync('mongodb://localhost:27017/test')
    .then(function(db) {
        return db.collection("myCollection").findOneAsync({ id: 'someId' })
    })
    .then(function(item) {
      // Use `item`
    })
    .catch(function(err) {
        // An error occurred
    });

这会让你走得很远,除了它还有助于确保Cursor返回的对象Collection#find()也是有效的.在MongoDB JS驱动程序中,返回的游标Collection#find()不是从原型构建的.因此,您可以包装方法并每次都传播游标.如果您不使用游标,或者不想产生开销,则不需要这样做.这是一种方法:

Collection.prototype._find = Collection.prototype.find;
Collection.prototype.find = function() {
    var cursor = this._find.apply(this, arguments);
    cursor.toArrayAsync = Promise.promisify(cursor.toArray, cursor);
    cursor.countAsync = Promise.promisify(cursor.count, cursor);
    return cursor;
}

Answer 3

我知道这已经多次回答了,但我想补充一点关于这个主题的更多信息.根据Bluebird自己的文档,您应该使用'using'来清理连接并防止内存泄漏. 蓝鸟资源管理

我整个地方都看到了如何正确地做到这一点,信息很少,所以我想我会分享经过多次试验和错误后发现的东西.我在下面使用的数据(餐馆)来自MongoDB样本数据.你可以在这里得到它:MongoDB导入数据

// Using dotenv for environment / connection information
require('dotenv').load();
var Promise = require('bluebird'),
    mongodb = Promise.promisifyAll(require('mongodb'))
    using = Promise.using;

function getConnectionAsync(){
    // process.env.MongoDbUrl stored in my .env file using the require above
    return mongodb.MongoClient.connectAsync(process.env.MongoDbUrl)
        // .disposer is what handles cleaning up the connection
        .disposer(function(connection){
            connection.close();
        });
}

// The two methods below retrieve the same data and output the same data
// but the difference is the first one does as much as it can asynchronously
// while the 2nd one uses the blocking versions of each
// NOTE: using limitAsync seems to go away to never-never land and never come back!

// Everything is done asynchronously here with promises
using(
    getConnectionAsync(),
    function(connection) {
        // Because we used promisifyAll(), most (if not all) of the
        // methods in what was promisified now have an Async sibling
        // collection : collectionAsync
        // find : findAsync
        // etc.
        return connection.collectionAsync('restaurants')
            .then(function(collection){
                return collection.findAsync()
            })
            .then(function(data){
                return data.limit(10).toArrayAsync();
            });
    }
// Before this ".then" is called, the using statement will now call the
// .dispose() that was set up in the getConnectionAsync method
).then(
    function(data){
        console.log("end data", data);
    }
);

// Here, only the connection is asynchronous - the rest are blocking processes
using(
    getConnectionAsync(),
    function(connection) {
        // Here because I'm not using any of the Async functions, these should
        // all be blocking requests unlike the promisified versions above
        return connection.collection('restaurants').find().limit(10).toArray();
    }
).then(
    function(data){
        console.log("end data", data);
    }
);

我希望这可以帮助其他想要通过蓝鸟书做事的人.

Answer 4

版本1.4.9 mongodb现在应该很容易实现:

Promise.promisifyAll(mongo.Cursor.prototype);

有关详细信息,请参阅https://github.com/mongodb/node-mongodb-native/pull/1201.