Create a post route that adds references to its relations - express

Question

I've got the basic MERN Stack app running I can, GET, POST and Delete Topics and Post separately, they have relationship in Schema but I don't understand how to route it properly to incorporate the relations when POSTing.
const express = require('express');
const router = express.Router();
const Post = require("../../models/Post");
const Topic = require('../../models/Topic');
router.post("/", (req,res) => {
//gets topic id from param
const {topic} = req.params;
//creating a new post
const newPost = new Post({
post: req.body.post,
description: req.body.description,
topic_id: req.body.topic_id
});
//get topic by id
const topic_obj = Topic.findById(topic);
//add posts to topic_object
topic_obj.posts.push(newPost);
//and save
topic_obj.save()
.then(newPost.save()
.then(post => res.json(post)).catch(err => console.log(err)));
});
module.exports = router;
I Don't know if you need more information
I pushed it to GitHub for some helpL https://github.com/wolffles/bloccit-node/blob/react/routes/api/posts.js

Answer 1

Accoarding to TopicSchema:
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
}});
To incorporate relation between Topic and Post you need to add _id property of newly created Post object to posts field in Topic object that this newly created Post represents.
topic_obj.posts.push(newPost._id);
EDIT:
In your code there are some issues that an cause errors.
const {topic} = req.params; You should validate whether topic is a valid ObjectId
You should also validate request body and check if description and post has required format.
You dupicate Topic id by passing it in request body and also asa request param.
const topic_obj = Topic.findById(topic); This is an async operation, it returns Promise not result of query.
Code should look like (it is not tested):
const express = require("express");
const router = express.Router();
const Post = require("../../models/Post");
const Topic = require("../../models/Topic");
router.post("/:topicId", async (req, res) => {
const { topicId } = req.params;
//TODO: validate if topic is a valid ObjectID
const validTopicId = validateTopicId(topicId);
if (!validTopicId) return res.status(400).send("Invalid param.");
//TODO: validate req.body.description and req.body.post
const validBody = validateBody(req.body);
if (!validBody) return res.status(400).send("Invalid data.");
const newPost = new Post({
post: req.body.post,
description: req.body.description,
topic_id: topicId
});
const topic = await Topic.findById(topicId);
if (!topic) return res.status(400).send("Invalid param.");
topic.posts.push(newPost._id);
await topic.save();
await newPost.save();
res.send();
});
module.exports = router;