承诺(promises)
原文:Built-in Promises 翻译:小虾米(QQ:509129)
Built-in Promises
Mongoose异步操作,像.save()
和查询,返回Promises/A+ conformant promises。这意味着你可以像MyModel.findOne({}).then()
和 MyModel.findOne({}).exec()
(如果你使用co包)。
为了向后兼容,Mongoose 4返回默认mpromise承诺。
var gnr = new Band({
name: "Guns N' Roses",
members: ['Axl', 'Slash']
});
var promise = gnr.save();
assert.ok(promise instanceof require('mpromise'));
promise.then(function (doc) {
assert.equal(doc.name, "Guns N' Roses");
});
Queries are not promises
Mongoose查询不是承诺。然而,他们也有一个.then()
功能为产量和异步/等待。如果你需要一个完全成熟的承诺,用.exec()
功能。
var query = Band.findOne({name: "Guns N' Roses"});
assert.ok(!(query instanceof require('mpromise')));
// A query is not a fully-fledged promise, but it does have a `.then()`.
query.then(function (doc) {
// use doc
});
// `.exec()` gives you a fully-fledged promise
var promise = query.exec();
assert.ok(promise instanceof require('mpromise'));
promise.then(function (doc) {
// use doc
});
Plugging in your own Promises Library
Mongoose 4.1.0 新特性
而mpromise满足基本使用的情况下,高级用户可能想插上自己喜欢的ES6风格承诺类库像bluebird,或只使用本地的ES6承诺。只需要设置mongoose.Promise
到你喜欢的ES6风格承诺构造函数,mongoose会使用它。
随着本土承诺ES6Mongoose试验,bluebird和q。任何承诺类库,理论上导出一个ES6风格的构造函数应该工作,但理论往往不同于实践。如果你发现一个bug,开放式问题在GitHub上。
var query = Band.findOne({name: "Guns N' Roses"});
// Use native promises
mongoose.Promise = global.Promise;
assert.equal(query.exec().constructor, global.Promise);
// Use bluebird
mongoose.Promise = require('bluebird');
assert.equal(query.exec().constructor, require('bluebird'));
// Use q. Note that you **must** use `require('q').Promise`.
mongoose.Promise = require('q').Promise;
assert.ok(query.exec() instanceof require('q').makePromise);
Promises for the MongoDB Driver
mongoose。承诺的属性集的mongoose用承诺。然而,这并不影响底层的MongoDB的驱动程序;。如果你使用了底层的驱动程序,例如Model.collection.db.insert()
,你需要做一些额外的工作来改变其所承诺的类库。注意,下面的代码假定mongoose> = 4.4.4。
var uri = 'mongodb://localhost:27017/mongoose_test';
// Use bluebird
var options = { promiseLibrary: require('bluebird') };
var db = mongoose.createConnection(uri, options);
Band = db.model('band-promises', { name: String });
db.on('open', function() {
assert.equal(Band.collection.findOne().constructor, require('bluebird'));
});
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