ReactJS - 使用来自 Firebase 的数据进行渲染重定向 - “渲染没有返回任何内容”

Question

I am fetching an URL from a collection in Firebase linked to an alias field. This part of code is OK, but I can't manage to make a Redirect with the URL field of retrieved data. Here is my code:

import React from 'react'
import { useParams, Redirect } from 'react-router-dom'
import { FirebaseContext } from '../firebase'

function RedirUrl () {
  const { alias } = useParams()
  let link = ''
  const { firebase } = React.useContext(FirebaseContext)
  const dbRef = firebase.db.collection('links')

  function getRedir () {
    dbRef.where('alias', '==', alias).get().then(snapshot => {
      link = snapshot.docs.map(doc => {
        return { ...doc.data() }
      })
      console.log(link[0].longUrl) // it is okay
      return link[0].longUrl
    })
  }
  return <Redirect to={getRedir()} />
}

export default RedirUrl

And here the warning message:

Warning: Failed prop type: The prop to is marked as required in Redirect , but its value is undefined

I guess the page is rendering before the retrieved data. Any help is appreciated.

Answer 1

<Redirect to={getRedir()} />

Here you are passing a promise to the to prop, but it should receive a string. You can use useEffect for getting the data from firebase:

const { alias } = useParams();
const { link, setLink } = useState('');
const { firebase } = React.useContext(FirebaseContext);
const dbRef = firebase.db.collection('links');

useEffect(() => {
    dbRef
        .where('alias', '==', alias)
        .get()
        .then((snapshot) => {
            const links = snapshot.docs.map((doc) => {
                return { ...doc.data() };
            });
            console.log(links[0].longUrl); // it is okay
            setLink(links[0].longUrl);
        });
}, []);
return link ? <Redirect to={link} /> : <></>;