Although MongoDB doesn't support joins, it does support the reference of a document to another document using a convention named DBRef. Mongoose includes support for DBRefs using the ObjectID schema type and the use of the ref property. Mongoose also supports the population of the parent document with the child document when querying the database.
To understand this better, let's say you create another schema for blog posts called PostSchema. Because a user authors a blog post, PostSchema will contain an author field that will be populated by a User model instance. So, a PostSchema will have to look like the following code snippet:
var PostSchema = new Schema({
title: {
type: String,
required: true
},
content: {
type: String,
required: true
},
author: {
type: Schema.ObjectId,
ref: 'User'
}
});
mongoose.model('Post', PostSchema);Notice the ref property telling Mongoose that the author field will use the User model to populate the value...