Joining Two Collections In A Mongoose With Example
In this tutorial, we are learning mongoose join two collections with example. As we saw earlier in MySQL, how we join tables, we will join the collection in mongoose, we will see below.
In mongoose, the alternative is called populate(). This process automatically replacing (update) the specified path (schema Id) in the document, with a document from a different model.
We have already installed Mongoose in Node.js and are creating APIs with the help of the Express framework. You can do any other work like building a website.
Mongoose Join Two Collections Create Schema
We will make Schema a user and another post as you see below
const { Schema, model} = require("mongoose");
const UserSchema = new Schema({
name:{
type: String,
required: true
},
email:{
type: String,
required: true
},
posts:[{
type: Schema.Types.ObjectId, ref: "Post"
}]
});
const PostSchema = new Schema({
title: String,
desc: String,
User: {type: Schema.Tpes.ObjectId, ref: "User"}
});
export const Post = model("Post", PostSchema);
export const User = model("User", UserSchema);
Above we saw how we two make Schema and match the object_id. This Schema Users and posts, User's Schema property called a posts Schema that references an array for Post'id and Post's Schema called user Schema reference a User's id.
Then, Saving references to other documents works the same way you normally save properties, just assign the _id value:
try {
const user = User.create({
name:"Robert Look",
email: "phpcodingstuff@gmail.com"
})
try {
const post1 = Post.create({
title: "This is a first post",
desc: "this a a first description"
user: User._id // assign the _id from the user
});
} catch (err) {
console.log(err.message)
}
} catch (err) {
console.log(err.message)
}
Reading Models
Now that our tables reference one another, let’s take a look at populating our post’s user using the populate() query builder:
User.findOne({
name: "Robert Look"
}).populate('posts').exec((err, user) =>{
if(err){
console.log(err)
}else{
console.log(users.posts[0].desc)
}
});
Conclusion
We saw above how to use populate We also saw how joining two documents in mongoose (MongoDB), if you write the query correctly then you will get a good result or your JSON.
I hope it can help you...
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