React Native w/ firebase “未定义不是对象”

Question

Getting this error:

TypeError: undefined is not an object (evaluating 'doc.data().books')

from this code:

    const getData = () => {
        const snapshot = db.collection('users').doc(userEmail).onSnapshot((doc) => {
            setData(doc.data().books)
        })

    }

    useEffect(() => {
        getData()
    }, [])
 

this is the firestore database, trying to get to the updated boo collection (gets shown in a flatlist that needs to get updated when new content is added to the collection) Note that there's a users collection that is offscreen.

I'm pretty sure it's something that I'm doing wrong on my snapshot but I'm really not sure what, all help is greatly appreciated:)

Answer 1

The error is telling you that doc.data() returned undefined, which means the document you requested doesn't exist. You probably passed a value for userEmail other than what you expected it to be. Since you didn't show the value, we don't know for sure what went wrong.

I will point out that document IDs must be exact matches, so if the email address wasn't exactly "Email@email.com" with a capital E, the query will not return a document using what you've shown here.

Answer 2

There are several possibilities. However, db is not defined within the scope of the getData function... where is it defined?

Answer 3

If I correctly understand your question, you want to get the documents in the books (or boo ?) subcollection of the user document with id corresponding to userEmail .

If this assumption is correct, you should do as follows:

const getData = () => {
    db.collection('users').doc(userEmail).collection('books')
       .onSnapshot(querySnapshot => {
           var books = [];
           querySnapshot.forEach(doc => {
               books.push(doc.data());
           });
           // Here you have an array of all the book objects.
           // It's up to you to use it as you wish with your setData() function
       });

}

---

Note that with doc.data().books you are actually trying to get the books field of the user doc.