Add lodash docs explaining that you shouldn't deepClone() documents

[piyushk96]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the bug has not already been reported

Mongoose version

6.6.5

Node.js version

16.15.1

MongoDB server version

4.4.13

Typescript version (if applicable)

No response

Description

In continuation to #6507. Lodash cloneDeep is now working perfectly when there is single level array subdocuments as mentioned in this comment but mongoose is still throwing following error when there is array of array subdocuments

myProject/node_modules/mongoose/lib/types/ArraySubdocument.js:149
  return this.__parentArray.$path() + '.' + this.__index + '.' + path;
                            ^
TypeError: this.__parentArray.$path is not a function
    at EmbeddedDocument.ArraySubdocument.$__pathRelativeToParent (/Users/myuser/myProject/node_modules/mongoose/lib/types/ArraySubdocument.js:149:29)
    at EmbeddedDocument.Subdocument.$isValid (/Users/myuser/myProject/node_modules/mongoose/lib/types/subdocument.js:150:25)
    at /Users/piyushkakkar/office/preppapi/node_modules/mongoose/lib/document.js:2802:18
    at processTicksAndRejections (node:internal/process/task_queues:78:11)

Steps to Reproduce

Demo Code:

const cloneDeep = require('lodash.cloneDeep');
const mongoose = require('mongoose');

async function run() {
  await mongoose.connect('mongodb://localhost:27017/test5');
  const arr2Schema = new mongoose.Schema({ _id: false, prop1: String });
  const arr1Schema = new mongoose.Schema({ _id: false, arr2: [arr2Schema] });
  const Test = mongoose.model(
    'Test',
    new mongoose.Schema({
      arr1: [arr1Schema],
      field: String,
    }),
  );

  let doc = new Test({ arr1: [{ arr2: [{ prop1: 'test' }] }] });
  await doc.save();

  const doc2 = await Test.findById(doc._id);
  const newDoc = cloneDeep(doc2).set({ field: 'test' });

  await newDoc.save(); // throws error
  console.log(newDoc);
}

run().catch((err) => console.log(err));

run this js script

Expected Behavior

Document should be updated without any error

[IslandRhythms]

const cloneDeep = require('lodash/cloneDeep'); // fixed import
const mongoose = require('mongoose');

async function run() {
  await mongoose.connect('mongodb://localhost:27017/test5');
  const arr2Schema = new mongoose.Schema({ _id: false, prop1: String });
  const arr1Schema = new mongoose.Schema({ _id: false, arr2: [arr2Schema] });
  const Test = mongoose.model(
    'Test',
    new mongoose.Schema({
      arr1: [arr1Schema],
      field: String,
    }),
  );

  let doc = new Test({ arr1: [{ arr2: [{ prop1: 'test' }] }] });
  await doc.save();

  const doc2 = await Test.findById(doc._id);
  const newDoc = cloneDeep(doc2).set({ field: 'test' });

  await newDoc.save(); // throws error
  console.log(newDoc);
}

run().catch((err) => console.log(err));

[vkarpov15]

I took a look and unfortunately we can't support cloneDeep() on documents with arrays in Mongoose 6. cloneDeep() has no way of knowing whether an object is a proxy, and we switched to using proxies for arrays in Mongoose 6.

We're planning on shipping a $clone() function in v6.8 that will allow you to do the following. See #11849 and #12549 for more info.

  const doc2 = await Test.findById(doc._id);
  const newDoc = doc2.$clone().set({ field: 'test' });

  await newDoc.save(); // works
  console.log(newDoc);

In the meantime, since $clone() isn't shipped yet, you should do the following:

  const doc2 = await Test.findById(doc._id);
  const newDoc = new Test().init(doc2.toObject()).set({ field: 'test' });

  await newDoc.save(); // works
  console.log(newDoc);