Reactnative：查询和过滤 Firestore 数据库并将单个返回的文档字段值保存在 const/var 中

Question

I have setup a Firebase Firestore Database and would like to filter it for a certain field value in a document. I have a collection called "PRD" with thousands of documents where all contain the same fields. One of these fields a Document contains is a GTIN Number (String). I am receiving this Number from a Bar Code (called data), and would like to retrieve the Medication Name (called DSCRD, a different Field in all these Documents) using the GTIN Number scanned.

I am having difficulties with retrieving the Value from the Firebase and the documentation doesn't seem to get me any further. I have tried various retrieval methods. At the moment the code for retrieval looks like this:

import { dbh } from "../firebase/config"
import firestore from '@react-native-firebase/firestore'

    dbh.collection('PRD')
    .where('GTIN', '==', data)
    .get()
    .then(documentSnapshot => {

      console.log('MedData',documentSnapshot.data())    
    });

I am unsure how to filter the right medicament using the GTIN provided by the Barcode scanner and then save the specific field value for the description of this medicament to a variable.

Firebase is setup correctly since I am able to write whole collections and documents in it.

Here is the database structure, as you can see there is the PRD Collection with all the medicaments and every medicament containing the GTIN and DSCRD Fields:

Answer 1

The problem with your implementation is that you are trying to call documentSnapshot.data() after querying a collection. This is the syntax you would use if you were fetching a single document. Your current query will return a list of documents which you need to handle like this:

.then(querySnapshot => {
  querySnapshot.forEach(doc => {
    console.log('MedData', doc.data())  
  })  
});

Assuming that the GTIN will fetch one unique document (will it?) then you can just use the only document returned by the query to get the name of the Medication like this:

    var medName
    dbh.collection('PRD')
    .where('GTIN', '==', data)
    .get()
    .then(querySnapshot => {
       querySnapshot.forEach(doc => {
          console.log('MedData', doc.data())  
          medName = doc.data().DSCRD
       })  
    });