Schema field is not being populated using mongoose populate

Question

Here is my model:

const postSchema = Schema({
  _id: Schema.Types.ObjectId,
  name: String,
  comments: Array
});

const Post = mongoose.model(“Post”, postSchema);
module.exports = Post;

Here is my code making a request to another microservice to populate the comments array, but it is empty, and is not being populated:

const UserPost = require(“./PostSchema”);

router.get("/post/list", async (request, response) =>{

try {
    let myUserPost = await UserPost.find();



    let postComments = await Promise.all(
        myUserPost.map((post) =>{
            
            axios.get(`${process.env.COMMENTS_MICROSERVICE_URL}/router/comments/list/comments/by/post/${post._id}`)
   .then((resp) => {
         resp.data.message.map((comment) =>{
    
                    
                    if(String(post._id) === comment.postID){
                        //console.log("post._id: ", post._id);

 /*** Desired, but does not work
    return UserPost.findById(post._id).populate('comments').exec();  */

 //The following alternative (embedding) works but adds the data to array
/***return UserPost.findByIdAndUpdate(post._id, {$addToSet: {"comments": comment}}, (err, data) =>{
err ? console.log(err) : console.log("aa: ", data);
     });   */  
                    }else{
                        console.log("no")
    
                    }
                    
                });
            })
            
        })
    );  

        
             

    return response.status(200).json({message: myUserPost});
}catch(err){
    return response.status(400).json({message: `${err}`});
}
});

What’s the best way to go about this and have it populate the comments field?

Answer 1

1. You are missing the ref attribute from the model declaration:

const postSchema = Schema({
    _id: {
        type: Schema.Types.ObjectId,
        ref: 'comments'
    },
    name: String,
    comments: Array
  });
  
  const Post = mongoose.model(“Post”, postSchema);
  module.exports = Post;

2. You should call exec after the populate method.
   

UserPost.findById(post._id).populate('comments').exec();