Reference array elements in same document of mongodb - mongodb

Question

This is the mongo schema-
{
name: String
description: String,
array1: [{prop1: Number, prop2: String}],
referencingArray: {prop1: String, prop2_array1ref: <array1 element ref>},
}
Array elements of type object. One of the properties in referencingArray object need to refer to an element from array1. The UI will later use the referenced array element to annotate referencingArray info. The UI also needs to update referencingArray based on changes to array1. Currently array1 objects do not have any uniquely identifying property.
One idea I have is to add a guid property to array1 objects to uniquely identify them and make the referencingArray object's prop2_array1ref to use this guid. But that adds an extra property on the array1 objects.
Referring to array1 objects via index will need to handle delete from array1. If prop2_array1ref is referring to index 0 element of array1, deleting the element at index 0 should put referencingArray in a bad state instead of silently referring to the new object at index 0.
Mongo assigns _id property to array objects. I thought of using the _id property of array objects in prop2_array1ref but I am not sure how to handle new entries when the array objects don't have an id yet.
Question:
What's the best way to refer array1 elements from referencingArray?
Edit to add example:
{
name: 'John',
description: 'Best guy',
array1: [
{prop1: 12, prop2: 'lorem'},
{prop1: 55, prop2: 'ipsum'}
],
referencingArray: {prop1: 'domur', prop2_array1ref: <array1 element 1 ref>},
// User can change prop2_array1ref to point to different element of array1 in UI.
// Question is what's a good value for prop2_array1ref?
// Options are-
// 1. Add guid to array1 elements and use that as value of prop2_array1ref. (e.g. 'fl3-42mnj-348hn-83ngns')
// 2. index of array1 elements. (e.g. 1)
// 3. mongo assigned _id of array1 elements. (e.g. 98702398420398)
}

Answer 1

A simple normalization will do the job:
your main model
{
name: String
description: String,
array1: [{type: Schema.Types.ObjectId, ref: 'Array1Model'}],
referencingArray: {prop1: String, prop2_array1ref: {type: Schema.Types.ObjectId, ref: 'Array1Model'}},
}
Array1Model
{
prop1: Number
prop2: String
}
As you said yourself, mongo will implicitly add the primary key. Later on, if you want to render them nicely on the frontend, you do a simple "join"-like operation using $lookup. Here's an example.