如何在一次调用中获取Firebase中的子集合的子集合

const parentCollectionRef = firebase.firestore().collection('parentCollection');
const query = parentCollectionRef.where('field', '==', 'value');

query.get().then((querySnapshot) => {
  querySnapshot.forEach((doc) => {
    const parentDocId = doc.id;
    const childCollectionRef = parentCollectionRef.doc(parentDocId).collection('childCollection');
    const childQuery = childCollectionRef.where('field', '==', 'value');

    childQuery.get().then((childQuerySnapshot) => {
      childQuerySnapshot.forEach((childDoc) => {
        console.log(childDoc.data());
      });
    });
  });
});