Mapping data from two Firestore collections with js [duplicate]

问题

I have two collections namely:CURRENCY-PAIR and Alerts.

The CURRENCY-PAIR collection contains the following;

Currency-Pair Name
Currency-AskPrice
Currency-BidPrice

The Alerts collection contains the following:

Alert_id
Alert_Status

How can i map the Currency-Pair Name from the CURRENCY-PAIR collection and Alert_Status from the Alerts collection to a list showing both.

回答1:

Say you want to fetch a collection of data from firestore, you should first get the reference of the collection:

const currencyRef = firestore().collection('CURRENCY-PAIR');
const alertRef = firestore().collection('Alert_Status');

You could then use these references to get the data from firestore:

currencyRef.get()
  .then((doc) => {
    console.log(doc.data());
  });

As you can see, the data is in the form of a promise, which you have to resolve. The doc.data() is an array of all the data in your collection, in the form of JS objects.

Since the data comes as a promise, you can create an async fetch function, which resolves the promise, and puts the data in a new array which gets returned. Maybe you can do something like this:

const fetchAllCurrencies = async () => {
  const obj = []; // empty array to put collections in
  const currencyRef = firestore().collection('CURRENCY-PAIR'); // ref
  const snapshot = await currencyRef.get() // resolve promise from firestore
  snapshot.forEach((doc) => { // loop over data
    obj.push({ id: doc.id, ...doc.data() }); // push each collection to array
  });
  return obj; // return array with collection objects 
}

You may create a similar function for the alert collection.

I'm not entirely sure about what you mean with: 'How can i map the Currency-Pair Name from the CURRENCY-PAIR collection and Alert_Status from the Alerts collection to a list showing both.'

by creating functions like the one above, you can get arrays of collection js objects. You can combine two arrays with: