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mongoose: Referencing schema in properties or arrays | Alexander Zeitler

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mongoose: Referencing schema in properties or arrays | Alexander Zeitler Toggle navigation Home Feed mongoose: Referencing schema in properties or arrays Written on February 01, 2015 When using a NoSQL database like MongoDb, most of the time you'll have documents that contain all properties by itself. But there are moreover scenarios where you might encounter the need for a increasingly relational tideway and need to reference other documents by the ObjectIds. This post will show you how to deal with these references using Node.js and the mongoose ODM. Lets consider we'll have a users hodgepodge and a posts collection, thus we'll have a UserSchema as well as a PostSchema. Posts can be written by users and the can by commented by users. In this example, well reference the users in posts and comments by their ObjectId reference. The UserSchema is implemented straight forward and looks like this: var mongoose = require('mongoose'); var UserSchema = new mongoose.Schema({ name: String }); module.exports = mongoose.model("User", UserSchema); Beside the title property, the PostSchema moreover defines the reference by ObjectId for the postedBy property of the PostSchema as well as the postedBy property of the comments inside the comments variety property: var mongoose = require('mongoose'); var PostSchema = new mongoose.Schema({ title: String, postedBy: { type: mongoose.Schema.Types.ObjectId, ref: 'User' }, comments: [{ text: String, postedBy: { type: mongoose.Schema.Types.ObjectId, ref: 'User' } }] }); module.exports = mongoose.model("Post", PostSchema); Now lets create two users: require("./database"); var User = require('./User'), Post = require('./Post'); var alex = new User({ name: "Alex" }); var joe = new User({ name: "Joe" }) alex.save(); joe.save(); The interesting part of undertow is the megacosm and plane increasingly the query for posts. The post is created with the ObjectId references to the users. var post = new Post({ title: "Hello World", postedBy: alex._id, comments: [{ text: "Nice post!", postedBy: joe._id }, { text: "Thanks :)", postedBy: alex._id }] }) Now lets save the Post and without it got created, query for all existing Posts. post.save(function(error) { if (!error) { Post.find({}) .populate('postedBy') .populate('comments.postedBy') .exec(function(error, posts) { console.log(JSON.stringify(posts, null, "\t")) }) } }); As you can see, the we're using the populate function of mongoose to join the documents when querying for Posts. The first undeniability to populate joins the Users for the postedBy property of the posts whereas the second one joins the Users for the comments. The Post document in the database looks like this: { "_id" : ObjectId("54cd6669d3e0fb1b302e54e6"), "title" : "Hello World", "postedBy" : ObjectId("54cd6669d3e0fb1b302e54e4"), "comments" : [ { "text" : "Nice post!", "postedBy" : ObjectId("54cd6669d3e0fb1b302e54e5"), "_id" : ObjectId("54cd6669d3e0fb1b302e54e8") }, { "text" : "Thanks :)", "postedBy" : ObjectId("54cd6669d3e0fb1b302e54e4"), "_id" : ObjectId("54cd6669d3e0fb1b302e54e7") } ], "__v" : 0 } In contrast, the query result is a full document containing all User references for the Posts. [ { "_id": "54cd6669d3e0fb1b302e54e6", "title": "Hello World", "postedBy": { "_id": "54cd6669d3e0fb1b302e54e4", "name": "Alex", "__v": 0 }, "__v": 0, "comments": [ { "text": "Nice post!", "postedBy": { "_id": "54cd6669d3e0fb1b302e54e5", "name": "Joe", "__v": 0 }, "_id": "54cd6669d3e0fb1b302e54e8" }, { "text": "Thanks :)", "postedBy": { "_id": "54cd6669d3e0fb1b302e54e4", "name": "Alex", "__v": 0 }, "_id": "54cd6669d3e0fb1b302e54e7" } ] } ] You can find the source lawmaking for this sample in this GitHub repository. Please enable JavaScript to view the comments powered by Disqus. Copyright © Alexander Zeitler 2003 - 2016 | Impressum