I using Firebase as my data store. I have a Firestore data structure where documents in a parent collection (“organizations”) contain a subcollection (“rags”) that stores text chunks along with their corresponding vector embeddings.

I want to create a retriever that efficiently fetches the most relevant documents from a specific organization’s “rags” subcollection.

Here’s a simplified version of my current code:

const retrieverConfig = defineFirestoreRetriever({
    name: 'retriever',
    firestore: firestore,
    collection: 'organizations',
    ...options,
    embedder: textEmbeddingGecko
  })

This won’t retrieve the vectors from the subcollection since it is only looking at the parent collection ‘organizations’.

How do I create a custom retriever to query the subcollection?