如何在firebase触发器事件中检索子集合项的父项

const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();

exports.retrieveParentItem = functions.firestore
  .document('parentCollection/{parentId}/childCollection/{childId}')
  .onWrite((change, context) => {
    const parentId = context.params.parentId;
    const childId = context.params.childId;

    // 获取父项的数据
    return admin.firestore().collection('parentCollection').doc(parentId).get()
      .then(parentDoc => {
        if (parentDoc.exists) {
          const parentData = parentDoc.data();
          console.log('Parent Data:', parentData);
        } else {
          console.log('Parent item does not exist.');
        }
        return null;
      })
      .catch(error => {
        console.error('Error retrieving parent item:', error);
        return null;
      });
  });