How to return data from Firestore query to a FlatList

I’m new to React-Native and I am trying to return the array of data from the firstore query to the device screen where I can setDevices. I had this working using .get() and .then(), but I wasn’t getting the updated events, so I’ve moved to onSnapshot and seem to have data at the query end, but can’t get this set at the screen.

import React, { useEffect, useRef, useState } from "react";
import { Alert,FlatList,RefreshControl,StatusBar,Text,View } from "react-native";
import { TouchableOpacity } from "react-native-gesture-handler";
import styles from "./styles";
import { getDevices } from "../../services/devices";
import { useNavigation } from "@react-navigation/native";
import { Feather } from "@expo/vector-icons";
import CircularProgress from "react-native-circular-progress-indicator";
import { removeDevice } from "../../redux/actions";
import { useDispatch } from "react-redux";
import firebase from "firebase/app";
import "firebase/firestore";

const wait = (timeout) => {
  return new Promise((resolve) => setTimeout(resolve, timeout));
};

export default function DevicesScreen() {
  const [devices, setDevices] = useState([]);
  const [loading, setLoading] = useState(false);
  const componentMounted = useRef(true);
  const navigation = useNavigation();

  useEffect(() => {
    getDevices().then(setDevices)
  },[]);
  console.log()


TypeError: undefined is not an object (evaluating '(0, _devices.getDevices)().then')

This error is located at:
in DevicesScreen (created by SceneView)

This error appears. If I remove .then(setDevices) I can see the array of data on the console.log

import firebase from "firebase/app";
import "firebase/firestore";

export const getDevices = () => {
  firebase
    .firestore()
    .collection("device")
    .where("user_id", "==", "Rweeff9MO8XIDheZLx0HVbfaezy2")
    .get()
    .then((querySnapshot) => {
      querySnapshot.docs.map(doc => {
        let data =doc.data();
        console.log(data);
        return { id, ...doc };
      }
      )}
    )
  }

Thanks

Answer

There are several problems in your code.

1. You don’t return the Promises chain.
2. id is not defined. You need to do doc.id.

So the following should do the trick:

export const getDevices = () => {
    return admin   // <========= See the return here
        .firestore()
        .collection("projects")
        .get()
        .then((querySnapshot) => {
           return querySnapshot.docs.map(doc => ({  id: doc.id, ...doc.data() }));  
           // ^^^  See the return here
        });
      }