如何在react-native中从Firestore中读取子集合的文档字段

import React, { useEffect, useState } from 'react';
import { View, Text } from 'react-native';
import firebase from '@react-native-firebase/app';
import '@react-native-firebase/firestore';

const App = () => {
  const [data, setData] = useState([]);

  useEffect(() => {
    const unsubscribe = firebase.firestore()
      .collection('parentCollection') // 父集合
      .doc('parentId') // 父文档ID
      .collection('childCollection') // 子集合
      .onSnapshot((querySnapshot) => {
        const documents = querySnapshot.docs.map((doc) => ({
          id: doc.id,
          ...doc.data(),
        }));
        setData(documents);
      }, (error) => {
        console.error("Error fetching documents: ", error);
      });

    return () => unsubscribe();
  }, []);

  return (
    <View>
      {data.map((item) => (
        <Text key={item.id}>{item.fieldName}</Text> // 替换fieldName为实际的字段名
      ))}
    </View>
  );
};

export default App;