UUID VS MongoDB ObjectId

Question

I'm developing an application and I'm having some doubts about using MongoDB ObjectId instead UUID as Document ID.

I've read MongoDB documentation (Mongo v4.0 - Mongo v5.0) and it says that ObjectId creation consists of:

• a 4-byte timestamp value, representing the ObjectId's creation, measured in seconds since the Unix epoch
• a 5-byte random value generated once per process. This random value is unique to the machine and process.
• a 3-byte incrementing counter, initialized to a random value

MongoDB ObjectId Documentation

So currently there is no problem using it because it doesn't specify a 3-byte machine id and a 2-byte process id as previously versions <4.0 and I undersand that is secure.

Following good practices, if I have the following Document, which option is better?

A:

{
  _id: ObjectId("5c593e5506b79bac64a5873e") //ObjectId
  id: "5c593e5506b79bac64a5873e" //String 
  ...
  subDocuments: [{
    _id: ObjectId("5c593e5506b79bac64a5873e") //ObjectId
    id: "5c593e5506b79bac64a5873e" //String 
  },{
   ...
  }]
}

This object contains the _id as string in "id" parameter to use it in frontend

B:

{
  _id: ObjectId("5c593e5506b79bac64a5873e") //ObjectId
  ...
  subDocuments: [{
    _id: ObjectId("5c593e5506b79bac64a5873e") //ObjectId
  },{
   ...
  }]
}

This document has no "id" parameter. It transforms _id ObjectId to string before send the data to frontend.

C:

{
  _id: ObjectId("5c593e5506b79bac64a5873e") //ObjectId
  id: UUID
  ...
  subDocuments: [{
    _id: ObjectId("5c593e5506b79bac64a5873e") //ObjectId
    id: UUID
  },{
   ...
  }]
}

This document uses UUID as "id" and ObjectId as "_id".

My current CONCLUSION:

I Should use ObjectId always less when I want to hide Doucment data creation because Mongo ObjectId specifies that timestamp.

Answer 1

If there is some value that is unique in the collection, you can use it as the _id and not use ObjectId at all. You lose the functionality provided by ObjectId to get the creation date of the document but, of course, you can use another field for that.

In your case, you don't need to generate a UUID to use it as the ID, the ObjectId is creating that unique key for you, so you can send the string with the ObjectId to the frontend and let Mongo create the ObjectIds for you in the database level.

It probably doesn't make to much sense to use both the ObjectId and a UUID field. Mongo creates a default index in the _id field and you probably need another one for the ìd field as well to be able to query by id efficiently, so the result is the collection has an extra field and an extra index that is really not needed.