Question 253042 in Javascript Question posted in
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Javascript – db request firebase with react

please can you help me to write this request in a new firebase notation please

useEffect(() => {
  let unsubscribe;
  if(postId){
    unsubscribe =db
    .collection("posts")
    .doc(postId)
    .colection("comments")
    .onSnapshot((snapshot)=>{
      setcomments(snapshot.doc.map((doc)=>doc.data()))
    })
  }
  
  
}, []);

best regards

im trying to write it but i dont how can i use "db.doc"
im writing somthing like that

useEffect(() => {
    onSnapshot(
      collection(db, "posts", "comments"),(snapshot) =>
        setcomments(
          snapshot.docs.map((doc) =>
            post: doc.data())
        )
    );
  }, []);

but it’s not work

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3

Answers


  1. Chosen as BEST ANSWER
    0

    thanks a lot my friend, but now, in my console, i have this error " Cannot access 'collection' before initialization" i show you my modification

    import { collection, onSnapshot } from "firebase/firestore";
import { useState, useEffect } from 'react';
import { db } from "./firebase";
const [comments, setcomments] = useState([])

      useEffect(() => {
      
      if(postId){
        const collection = collection(db, "posts", postId, "comments");
        const unsubscribe = onSnapshot(collection, (snapshot) => {
          setcomments(snapshot.doc.map((doc) => doc.data()));
        });
      }
      return ()=>{
        unsubscribe()
      }
      
      
    }, [postId]);

  2. 0

    The following should do the trick:

    import { collection, onSnapshot } from "firebase/firestore";

const collection = collection(db, "posts", postId, "comments");
const unsubscribe = onSnapshot(collection, (snapshot) => {
  // ...
});

    More details on how to declare sub-collections with the JS SDK v9 in this article.

    Login or Signup to reply.
  3. 0

    im fixed the probléme like that:

    import { collection, onSnapshot } from "firebase/firestore";
import { useState, useEffect} from 'react';
import { db } from "./firebase";


const [comments, setcomments] = useState([])
 useEffect(() => {
  let unsubscribe
  if(postId){

    unsubscribe = onSnapshot(collection(db, "posts", postId, "comments"), (snapshot) => {
      setcomments(snapshot.doc.map((doc) => doc.data()));
    });
  }
  return ()=>{
    unsubscribe()
  }
  }, [postId]);

    but now i have this error: "Uncaught TypeError: Cannot read properties of undefined (reading ‘map’) at Array."
    please can you help me?

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