Duplicate item returned from collection - node.js

Question

Blog Schema:
{
body: { type: String, required: true },
title: { type: String, required: true },
published: { type: String, default: false },
date: { type: Date, default: Date.now },
user: { type: Schema.Types.ObjectId, ref: 'BlogUser' },
comments: [{ type: Schema.Types.ObjectId, ref: 'Comments' }],
likes:[{user:{ type: Schema.Types.ObjectId, ref: 'BlogUser' }}]
}
Like Route for adding a like:
exports.likeBlog = async (req, res) => {
const blog_id = req.params.blog_id;
const user_id = req.body.user_id;
await Blog.findByIdAndUpdate(
blog_id,
{
$push: {
likes: {
user: user_id,
},
},
},
{ new: true },
(err, newBlog) => {
if (err) res.status(422).json(err);
console.log(newBlog);
res.json(newBlog);
}
);
};
Blog Route for reciveing a blog:
exports.getBlogByID = async (req, res) => {
const blog_id = req.params.blog_id;
try {
const blog = await Blog.findById(blog_id)
.populate("comments")
.populate("user");
console.log(blog);
res.json(blog);
} catch (error) {
res.status(401).json(error);
}
};
When I add a like by calling Like route from client, I get a blog with correct amount of likes i.e only 1. But when I request blog from Blog Route it returns me with two objects inside "likes" array, with both same as each other(same id too). Why am I getting such result? Mind you that I call 'Blog Route' after calling 'Like Route'.

Answer 1

It worked fine after I changed "like route" to this:
exports.likeBlog = async (req, res) => {
const blog_id = req.params.blog_id;
const user_id = req.body.user_id;
const blog = await Blog.findById(blog_id);
blog.likes.unshift({ user: user_id });
await blog.save();
Blog.findById(blog_id)
.then((result) => {
res.json(result);
})
.catch((error) => {
res.status(501).json({ error });
});
};
I still don't know what's the difference between the two though.