Error while deleting a value of element in mongoDB array using filter function?

Question

I tried to find the solutions over here but unable to get success while using $pull as the array values I have does not contain `mongo_id'.

So the scenario is that , I am trying to delete the specific comment of the particular user which I am passing through query params. M

My mongo data looks like this:

Now I am making API Delete request like this : http://localhost:8000/api/articles/learn-react/delete-comment?q=1 on my localhost .

ANd finally my code looks like this:

import express from "express";
import bodyParser from "body-parser";
import { MongoClient } from "MongoDB";



const withDB = async (operations, res) => {
try {
  const client = await MongoClient.connect(
  "mongodb://localhost:27017",
  { useNewUrlParser: true },
  { useUnifiedTopology: true }
 );
  const db = client.db("my-blog");

  await operations(db);

  client.close();
  } catch (error) {
   res.status(500).json({ message: "Error connecting to db", error });
  }
 };


app.delete("/api/articles/:name/delete-comment", (req, res) => {
 const articleName = req.params.name;
 const commentIndex = req.query.q;

 withDB(async(db) => {
   try{
     const articleInfo = await db.collection('articles').findOne({name:articleName});
     let articleAllComment = articleInfo.comments;
     console.log("before =",articleAllComment)
     const commentToBeDeleted = articleInfo.comments[commentIndex];
     //console.log(commentToBeDeleted)
     // articleAllComment.update({
     //   $pull: { 'comments':{username: commentToBeDeleted.username }}
     // });
     articleAllComment = articleAllComment.filter( (item) => item != commentToBeDeleted );
     await articleAllComment.save();

     console.log("after - ",articleAllComment);
     //yaha per index chahiye per kaise milega pta nhi?
     //articleInfo.comments = gives artcle comment
     res.status(200).send(articleAllComment);
   }
   catch(err)
   {
     res.status(500).send("Error occurred")
   }
   },res);

 });

I have used the filter function but it is not showing any error in terminal but also getting 500 status at postman.

Unable to figure out the error?

score 0 · Answer 1 · answered Oct 12 '21 at 02:18

I believe you'll find a good answer here: https://stackoverflow.com/a/4588909/9951599

Something to consider...

You can use MongoDB's built-in projection methods to simplify your code. https://docs.mongodb.com/manual/reference/operator/projection/positional/#mongodb-projection-proj.-

By assigning a "unique ID" to each of your comments, you can find/modify the comment quickly using an update command instead of pulling out the comment by order in the array. This is more efficient, and much simpler. Plus, multiple read/writes at once won't interfere with this logic during busy times, ensuring that you're always deleting the right comment.

Solution #1: The recommended way, with atomic operators

Here is how you can let MongoDB pull it for you if you give each of your comments an ID.

await db.collection('articles').updateOne({ name:articleName },
{
    $pull:{ "comments.id":commentID }
});
// Or
await db.collection('articles').updateOne({ name:articleName, "comments.id":commentID },
{
    $unset:{ "comments.$":0 }
});

Solution #2 - Not recommended

Alternatively, you could remove it by index:

// I'm using "3" here staticly, put the index of your comment there instead.
db.collection('articles').updateOne({ name:articleName }, {
    $unset : { "comments.3":0 }
})

I do not know why your filter is erroring, but I would recommend bypassing the filter altogether and try to utilize MongoDB's atomic system for you.

Although I am tryimg to delete without using findByIdandDelete(); But I am exploring other methods too. Coming to your answer, i.e. in `Solution#2` , you have statically used 3 but I have a variable `commentIndex` ,then how can I use it here,??? db.collection('articles').updateOne({ name:articleName }, { $unset : { `comments.${commentIndex}`:0 } }) I used it like above by using backticks & dollar like we do in javascript? — MagnusEffect, Oct 13 '21 at 00:07
Also your method 2 making null values which is creating problem — MagnusEffect, Oct 13 '21 at 00:12

Error while deleting a value of element in mongoDB array using filter function?

1 Answers1