未捕获的 FirebaseError：无效的文档引用。 文档引用必须有偶数个段，但 todos 有 1

Question

I'm getting the error: Uncaught FirebaseError: Invalid document reference. Document references must have an even number of segments, but todos has 1. Uncaught FirebaseError: Invalid document reference. Document references must have an even number of segments, but todos has 1.

I wrote code because I want to inquire the data in the DB.

No matter how much I searched, I couldn't find the answer. which part is wrong

this is my firebaseConfig code:

import firebase from "firebase/compat/app";
import "firebase/compat/firestore";
import "firebase/compat/auth";

const firebaseConfig = {
  apiKey: "***",
  authDomain: "***",
  projectId: "***",
  storageBucket: "***",
  messagingSenderId: "***",
  appId: "***",
  measurementId: "***",
};

firebase.initializeApp(firebaseConfig);

const firestore = firebase.firestore();

export { firestore };

export const auth = firebase.auth();

export const apiKey = firebaseConfig.apiKey;

this is code of firebaseController.tsx:

export const todos = firestore.collection('todos');

and this is code of view component:

useEffect(() => {
    onSnapshot(todos, (snapshot: QuerySnapshot<DocumentData>) => {
      setTodoItems(
        snapshot.docs &&
          snapshot.docs.map((doc) => {
            return {
              id: doc.id,
              ...doc.data(),
            };
          })
      );
    });
  }, []);

my database: DB

Answer 1

The onSnapshot method works on Firebase Documents, not on Firebase Collections. The first argument to onSnapshot you give ie "todos" is a collection reference but in reality, it expects a document reference, which you obtain by using the method

const docRef = doc(db, "path/to/document/inside/todos/collection")
onSnapshot(docRef, ......)

Hope this helps!