Mongoose - How to query self referencing relationship?

Question

I want to implement a parent/child (Self Referencing) relationship for comments with its replies, Here's the code for the schema:

const mongoose = require("mongoose");
const Schema = mongoose.Schema;

const BlogCommentSchema = new Schema({
  body: String,
  dateTime: { type: Date, default: Date.now },
  replies: [this]
});

const BlogComment = mongoose.model("blogComments", BlogCommentSchema);

module.exports = BlogComment;

What is the simplest way to get the number of comments or replies of a comment?

Any help would be appreciated.

Clarification: Here's an example of saved a document based on the schema:

{
  "replies": [
    {
      "replies": [
        {
          "replies": [],
          "_id": "5e558aa01f804205102b4a78",
          "body": "Comment 1.1.1",
          "dateTime": "2020-02-25T20:59:12.056Z"
        }
      ],
      "_id": "5e558aa01f804205102b4a79",
      "body": "Comment 1.1",
      "dateTime": "2020-02-25T20:59:12.057Z"
    },
    {
      "replies": [
        {
          "replies": [
            {
              "replies": [
                {
                  "replies": [
                    {
                      "replies": [],
                      "_id": "5e558aa01f804205102b4a7a",
                      "body": "Comment 1.2.1.1.1",
                      "dateTime": "2020-02-25T20:59:12.057Z"
                    }
                  ],
                  "_id": "5e558aa01f804205102b4a7b",
                  "body": "Comment 1.2.1.1.1",
                  "dateTime": "2020-02-25T20:59:12.057Z"
                }
              ],
              "_id": "5e558aa01f804205102b4a7c",
              "body": "Comment 1.2.1.1",
              "dateTime": "2020-02-25T20:59:12.057Z"
            }
          ],
          "_id": "5e558aa01f804205102b4a7d",
          "body": "Comment 1.2.1",
          "dateTime": "2020-02-25T20:59:12.058Z"
        }
      ],
      "_id": "5e558aa01f804205102b4a7e",
      "body": "Comment 1.2",
      "dateTime": "2020-02-25T20:59:12.058Z"
    }
  ],
  "_id": "5e558aa01f804205102b4a7f",
  "body": "Comment 1",
  "dateTime": "2020-02-25T20:59:12.058Z",
  "__v": 0
}

I need to get these numbers (total number of replies is 7, number of Comment 1.1 is 1, ...):

Comment 1 (count is 7)
  - Comment 1.1 (count 1)
    - Comment 1.1.1
  - Comment 1.2 (count 4)
    - Comment 1.2.1
      - Comment 1.2.1.1
        - Comment 1.2.1.1.1
          - Comment 1.2.1.1.1.1

It is not clear whether you want to get number of comments in top level or all comments hierarchically. Can you add sample documents and the expected document to the question? — SuleymanSah, Feb 25 '20 at 20:08
@SuleymanSah Well I need both. I have just updated my question. — Sirwan Afifi, Feb 25 '20 at 21:26
Does this answer your question? [Can a Mongo model self reference](https://stackoverflow.com/questions/24964914/can-a-mongo-model-self-reference) — Daniel W., Feb 25 '20 at 21:31
@DanielW. Thanks for sharing the link, I know Mongo can handle such relationship, my question is about querying a self-referenced schema not designing the schema. — Sirwan Afifi, Feb 25 '20 at 21:33
@SirwanAfifi Then try this github issue pls: https://github.com/Automattic/mongoose/issues/5083 — Daniel W., Feb 25 '20 at 21:37

score 2 · Accepted Answer · answered Feb 26 '20 at 08:22

I finally managed to get the result by adding a virtual type to my schema and use a recursive method to get the total number of replies:

const getRepliesCount = (comment, count = 0) => {
  if (comment.replies.length === 0) {
    return 1;
  }
  for (const reply of comment.replies) {
    count += getRepliesCount(reply, count);
  }
  return count;
};


BlogCommentSchema.virtual("total").get(function() {
  return getRepliesCount(this) + 1;
});

Although I was hoping there might be a built-in way or a proper way to do this using MongoDB/Mongoose.

Mongoose - How to query self referencing relationship?

1 Answers1