References in MongoDB

Question

I have an app where one document wants to reference another document, the catch here is the other documents could be in two different collections. is there a way to do it, keeping in mind I'm going to have to populate them when they are fetched.

const schemaOne = new Schema({
   name: string,
// other fields
})

const schemaTwo = new Schema({
   name: string
// other fields
})

const schemaThree = new Schema({
// I want to reference a document from schemaOne or two in one field
   someId: ObjectId,
})

The solution I'm not try to do is to create two fields one for the schemaOne and the other for schemaTwo. but this I think will create more complexity.

Answer 1

You can use refPath. This allows you to have a field in schemaThree that specifies which model to use when you populate.

const schemaThree = new Schema({
   someId: {
      type: Schema.Types.ObjectId,
      refPath: 'modelNameSpecifier', //< this is used during populate()
   },
   modelNameSpecifier: {
      type: String,
      required: true,
      enum: ['ModelOne', 'ModelTwo']
   }
});

const docs = await ModelThree.find({}).populate('someId');

When you create a document with ModelThree just make sure you save the ObjectId in the someId field of whichever schema relates to that Objectid in the modelNameSpecifier as either ModelOne for schemaOne or ModelTwo for schemaTwo.