我可以构建一个子集合吗？ （火库）

Question

I'm trying to figure out how to construct a new sub-collection (RED CIRCLE) inside the following directory in Firestore:

directory: "courses/{userID}/{courseID} "

with the courseID to be randomly generated ID upon creation of the sub-collection inside the "userID" document. Unfortunately the code I was able to get working, using the.set(), doesn't create a new sub-collection, but rather just updates the current document.

Is there a function that I can use to create a new collection inside the document?

CODE:

export const createCourse = (course) => {
    
    (...)

    //firestore.collection("courses").doc(authorId).set({   <---This commented out line updates the document, yet I'm trying to construct a new sub-collection inside this document, not just change fields inside of it. 
    firestore.collection("courses").doc(authorId).add({     <--- This gives me an error stating " firestore.collection(...).doc(...).add is not a function ".   I am trying to figure out what is the correct syntax for this intended action.
        ...course,
        authorUID: authorId,
        courseCreatedAt: new Date()
    }).then(() => {

    (...)

};

Answer 1

There is no API for what you're trying to do. Also, it's generally not a good idea to use random collection name to model your data. Collections names should be known by your app ahead of time, because:

1. It's not possible to query a collection if you don't know its name.
2. There are no client APIs to list subcollections under a document.

Consider instead using a subcollection named "courses", then add a document under there with a random ID.