我写这个数据作为一个例子。我有两个不同的集合books和publishers
"books": [
{
"isbn": "9781593275846",
"title": "Eloquent JavaScript, Second Edition",
"subtitle": "A Modern Introduction to Programming",
"author": "Marijn Haverbeke",
"published": "2014-12-14T00:00:00.000Z",
"_publisher": "5f35578bf55f6cef9fd6193f",,
"pages": 472,
"description": "JavaScript lies at the heart of almost every modern web application, from social apps to the newest browser-based games. Though simple for beginners to pick up and play with, JavaScript is a flexible, complex language that you can use to build full-scale applications.",
"website": "http://eloquentjavascript.net/"
},
{
"isbn": "9781449331818",
"title": "Learning JavaScript Design Patterns",
"subtitle": "A JavaScript and jQuery Developer's Guide",
"author": "Addy Osmani",
"published": "2012-07-01T00:00:00.000Z",
"publisher": "5f3557bd51bf64f398cb8853",,
"pages": 254,
"description": "With Learning JavaScript Design Patterns, you'll learn how to write beautiful, structured, and maintainable JavaScript by applying classical and modern design patterns to the language. If you want to keep your code efficient, more manageable, and up-to-date with the latest best practices, this book is for you.",
"website": "http://www.addyosmani.com/resources/essentialjsdesignpatterns/book/"
},
{
"isbn": "9781449365035",
"title": "Speaking JavaScript",
"subtitle": "An In-Depth Guide for Programmers",
"author": "Axel Rauschmayer",
"published": "2014-02-01T00:00:00.000Z",
"publisher": "5f3557bd51bf64f398cb8853",
"pages": 460,
"description": "Like it or not, JavaScript is everywhere these days-from browser to server to mobile-and now you, too, need to learn the language or dive deeper than you have. This concise book guides you into and through JavaScript, written by a veteran programmer who once found himself in the same position.",
"website": "http://speakingjs.com/"
},
{
"isbn": "9781491950296",
"title": "Programming JavaScript Applications",
"subtitle": "Robust Web Architecture with Node, HTML5, and Modern JS Libraries",
"author": "Eric Elliott",
"published": "2014-07-01T00:00:00.000Z",
"publisher": "5f3557bd51bf64f398cb8853",
"pages": 254,
"description": "Take advantage of JavaScript's power to build robust web-scale or enterprise applications that are easy to extend and maintain. By applying the design patterns outlined in this practical book, experienced JavaScript developers will learn how to write flexible and resilient code that's easier-yes, easier-to work with as your code base grows.",
"website": "http://chimera.labs.oreilly.com/books/1234000000262/index.html"
},
{
"isbn": "9781593277574",
"title": "Understanding ECMAScript 6",
"subtitle": "The Definitive Guide for JavaScript Developers",
"author": "Nicholas C. Zakas",
"published": "2016-09-03T00:00:00.000Z",
"publisher": "No Starch Press",
"pages": 352,
"description": "ECMAScript 6 represents the biggest update to the core of JavaScript in the history of the language. In Understanding ECMAScript 6, expert developer Nicholas C. Zakas provides a complete guide to the object types, syntax, and other exciting changes that ECMAScript 6 brings to JavaScript.",
"website": "https://leanpub.com/understandinges6/read"
},
{
"isbn": "9781491904244",
"title": "You Don't Know JS",
"subtitle": "ES6 & Beyond",
"author": "Kyle Simpson",
"published": "2015-12-27T00:00:00.000Z",
"publisher": "5f3557bd51bf64f398cb8853",
"pages": 278,
"description": "No matter how much experience you have with JavaScript, odds are you don’t fully understand the language. As part of the "You Don’t Know JS" series, this compact guide focuses on new features available in ECMAScript 6 (ES6), the latest version of the standard upon which JavaScript is built.",
"website": "https://github.com/getify/You-Dont-Know-JS/tree/master/es6%20&%20beyond"
},
{
"isbn": "9781449325862",
"title": "Git Pocket Guide",
"subtitle": "A Working Introduction",
"author": "Richard E. Silverman",
"published": "2013-08-02T00:00:00.000Z",
"publisher": "5f3557bd51bf64f398cb8853",
"pages": 234,
"description": "This pocket guide is the perfect on-the-job companion to Git, the distributed version control system. It provides a compact, readable introduction to Git for new users, as well as a reference to common commands and procedures for those of you with Git experience.",
"website": "http://chimera.labs.oreilly.com/books/1230000000561/index.html"
},
{
"isbn": "9781449337711",
"title": "Designing Evolvable Web APIs with ASP.NET",
"subtitle": "Harnessing the Power of the Web",
"author": "Glenn Block, et al.",
"published": "2014-04-07T00:00:00.000Z",
"publisher": "5f3557bd51bf64f398cb8853",
"pages": 538,
"description": "Design and build Web APIs for a broad range of clients—including browsers and mobile devices—that can adapt to change over time. This practical, hands-on guide takes you through the theory and tools you need to build evolvable HTTP services with Microsoft’s ASP.NET Web API framework. In the process, you’ll learn how design and implement a real-world Web API.",
"website": "http://chimera.labs.oreilly.com/books/1234000001708/index.html"
}
]
publishers: [
{
_id: "5f35578bf55f6cef9fd6193f",
name: "No Starch Press",
country: "USA",
foundeed: "1994"
},
{
_id: "5f3557bd51bf64f398cb8853",
name: "O'Reilly Media",
country: "USA",
foundeed: "1978"
}
]
我想用猫鼬和两个相关的查询来查询它们
第一个问题是，如果我通过publisherId，我想让出版商提供它的数据和属于该出版商的所有书籍。请注意，这些书有_publisher_id，但出版商没有书籍参考。
如果我做books.find({ _publisher: publisherId})，我会按出版商过滤书籍，但如果我想添加来自出版商的数据并填充，出版商的数据将显示在每本书的中
我想要的输出是
{
publisher: {
// publisherData
books : [
// filtered books
]
}
}
第二个查询是获取所有书籍，但按出版商分组。查询与第一个类似，但我不知道如何根据自己的喜好查询和投影输出，因为我没有关于书籍出版商的数组。
如果没有在两个方向上建立关系的数组字段，我不确定是否可以反转查询。
我认为您正在使用这样的管道查找$lookup：
https://mongoplayground.net/p/H_OsKvN_npf
db.publishers.aggregate([
{$lookup: {
from: 'books',
as: 'books',
let: {publisherId: '$_id'},
pipeline: [
{$match: {$expr: {
$eq: ['$publisher', '$$publisherId']
}}}
]
}}
])
然后要获得单个发布者，请添加一个匹配阶段：
db.publishers.aggregate([
{$match: {_id: mongoose.Types.ObjectId('YOUROBJECTID')}},
{$lookup: {
from: 'books',
as: 'books',
let: {publisherId: '$_id'},
pipeline: [
{$match: {$expr: {
$eq: ['$publisher', '$$publisherId']
}}}
]
}}
])