so I want to make a delete reply system but I don't know how to do it. Can you guy help me? This is my table image of my mongodb

and the code I've tried is but it doesn't work

app.post("/remove-reply", async (req, res) => {
const index = parseInt(req.body.index) - 1

await Posts.findOneAndUpdate({ _id: req.body.id }, [
    {
        $set: {
            "Comments.$[].replies": {
                $concatArrays: [
                    { $slice: ["$Comments.$[].replies", index] },
                    { $slice: ["$Comments.$[].replies", { $add: [1, index] }, { $size: "$Comments.$[].replies" }] }
                ]
            }
        }
    }
])
res.redirect("/")
})

and it gives me this error

    (node:17376) UnhandledPromiseRejectionWarning: MongoServerError: Invalid $set :: caused by :: FieldPath field names may not start with '$'.
    at MessageStream.messageHandler (C:\Users\The.Peerapon\Desktop\programming\Express-app\node_modules\mongodb\lib\cmap\connection.js:467:30)
    at MessageStream.emit (events.js:400:28)
    at processIncomingData (C:\Users\The.Peerapon\Desktop\programming\Express-app\node_modules\mongodb\lib\cmap\message_stream.js:108:16)
    at MessageStream._write (C:\Users\The.Peerapon\Desktop\programming\Express-app\node_modules\mongodb\lib\cmap\message_stream.js:28:9)
    at writeOrBuffer (internal/streams/writable.js:358:12)
    at MessageStream.Writable.write (internal/streams/writable.js:303:10)
    at TLSSocket.ondata (internal/streams/readable.js:731:22)
    at TLSSocket.emit (events.js:400:28)
    at addChunk (internal/streams/readable.js:293:12)
    at readableAddChunk (internal/streams/readable.js:267:9)
(Use `node --trace-warnings ...` to show where the warning was created)
(node:17376) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 1)
(node:17376) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

my goal is to click delete button at reply to delete it by index.

CodePudding user response：

for each comment\reply, save its index in the database and use it as a sort of id. then, when someone wants to delete a comment, you do the following:

app
  .post('/remove-reply', async (req, res) => {
    const postId = req.body.id;
    const commentIndex = parseInt(req.body.commentIndex) - 1;
    const replyId = req.body.replyIndex;
    await Posts.findOneAndUpdate({
      _id: postId
    }, {
      $pull: {
        [`Comments.${ commentIndex }.replies`]: {
          _id: replyId 
        }
      }
    });
    res.redirect('/');

  });

so, when a user clicks on a reply to delete, you should have all 3 fields you need for finding the exact reply you want to delete.

You can also just save an auto-generated unique id for each item to use as an identifier\index since we treat it as a collection more than an array in this use-case. It will probably be easier to maintain since after deleting a comment, the index is not aligned anymore with the underlying array.