Array of different schemas

[vnugent]

My audit_logs collection tracks changes to a few collections (via change streams). Depending on the user actions, the changes array can contain documents with the same schema or different schemas. In this example, profile and account have a different schema.

How do you define the schema for changes? Using array of Mixed type? (https://mongoosejs.com/docs/schematypes.html#mixed)

# audit_logs collection
[
    {
      _id: new ObjectId("62dd9815b11c3e3e3d01a41c"),
      editedBy: new Binary(Buffer.from("a927c2893cc64963b67f560c81a5dffa", "hex"), 4),
      operation: 'addNewUser',
      createdAt: 2022-07-24T19:05:57.855Z,
      changes: [
           {
               # 'profile' fullDocument captured by  event stream
           },
           {
               # 'account' fullDocument captured by event stream 
           }
      ]
    }
   ...
]

[vkarpov15]

Do you know the model's type in audit_logs? If you do, you can use discriminators, or manually hydrate() the changes subdocuments. If not, need to use mixed.

[vnugent]

Yes, I have a schema defined for audit_log. The reason I'm wanting to embed changes is to avoid join/lookup multiple collections.

I've just looked at Discriminators docs. I'm not sure how to use it as an array.

[vkarpov15]

For this use case, I think you're better off storing changes as an array of mixed. new Schema({ changes: [] }). And then hydrate the individual documents using const account = Account.hydrate(auditLog.changes[0]); // assuming changes[0] is an account . Discriminators would be a bit trickier to implement because you have a bunch of top-level models with potentially different options.