How to push reference and save via POST API in NodeJs?

Question

Using express.js framework for MERN stack app. It's my first js full stack app, so new to a lot of these functions. Need to POST a new post to a topic and also update topic. Posts with a reference to the Posts collection.

Here's server.js :

router.post('/:id/posts', (req,res) => {
  const { id } = req.params // works

  const newPost = new Post({
    post: req.body.post,
    description: req.body.description,
    topic_id: id
  })

  const topic = Topic.findById(id).then(topics => res.json(topics))

  console.log(topic.posts)
  // and I don't understand why my topic object is always undefined I need to push a reference into it I think.

  //need to save/update topic object to db
  //need to save new post
  //my other post function has newPost.save().then(post => res.json(post) and it works. but in this function it doesn't. 
});

this is the schema

const TopicSchema = new Schema({
    topic: {
        type: String,
        required: true
    },
    description: {
        type: String,
        required: true
    },
    posts: [
        { 
            type: Schema.Types.ObjectId,
            ref: 'post'
        }
    ],
    date: {
        type: Date,
        default: Date.now
    }
});   

If anyone could walk me through what I'm doing wrong I'd be grateful. Also pushed to GitHub if more info is needed

line 31 is the code snippet.

Answer 1

To save do this:

const topic = Topic.findById(id).then(topic => {
    topic.posts.push(newPost);
    topic.save(err => {
       if (err) {
         res.sendStatus(400)
       } else {
         res.sendStatus(200)
       }
    })
})

You can query by topic ID in the save callback if you want to send the updated topic back to client.

Answer 2

This line is wrong

const topic = Topic.findById(id).then(topics => res.json(topics))

Here you are doing asynchronoous call so topic will be a promise and topic.posts will be undefined (normal)

It's look like your using TypeScript or Ecmascript so you could do : (look at async and await keyword)

router.post('/:id/posts', async (req,res) => {

  const { id } = req.params // works

   const newPost = new Post({
     post: req.body.post,
     description: req.body.description,
     topic_id: req.body.id
   })

   try {
     const topic = await Topic.findById(id);
   }catch(err){
      // send a status 404 cause the id dont match any topic
      return;
   }
   console.log(topic.posts) //undefined but i still need to add post._id to my topic.posts 

     //attempt to save newPost object
   try {
     const post = await newPost.save();
     res.json(post);
   }catch(err){
      // You can send a internal error status cause something went wrong
   }
     // returns not post json but a topic json?
     // plus error
});