I ran into this issue as well. My fix was to create a child schema. See below for an example for your models.
---- Person model
const mongoose = require('mongoose');
const SingleFriend = require('./SingleFriend');
const Schema = mongoose.Schema;
const productSchema = new Schema({
friends : [SingleFriend.schema]
});
module.exports = mongoose.model('Person', personSchema);
***Important: SingleFriend.schema -> make sure to use lowercase for schema
--- Child schema
const mongoose = require('mongoose');
const Schema = mongoose.Schema;
const SingleFriendSchema = new Schema({
Name: String
});
module.exports = mongoose.model('SingleFriend', SingleFriendSchema);