How to fetch firestore data via reference value in a key - firebase

Question

here is the multiple document for offer and each offer cantains bidderId that is referenced to users collection and user id.
I want to fetch offer list contains user collection.
I am using angularfire and here is my code.
this.liveOffers=this.db.collection("offers",ref => ref.where('offerExpired', '==', 0).where('isStart', '==', 1)).snapshotChanges().pipe(
map(actions => actions.map(a => {
const data={} = a.payload.doc.data() as offer;
const id = a.payload.doc.id;
var bidder=this.db.doc(data.bidderId).snapshotChanges().subscribe(key=>{
console.log(key.payload.data());
});
return { id, ...data,bidder };
})) );
Here console.log(key.payload.data()); is logging the data for user but it can not bind with bidder variable and i can not use the user object in front end.
Please let me know how can I fetch the offer record with user details.

Answer 1

You need to use a combination of switchMap and combineLatest to get it done.
This is a pseudo-code approach
const temp = []
this.offers$ = this.db.collection().snapshotChanges().pipe(
map(auctions=>{
//we save all auctions in temp and return just the bidderId
return auctions.map(auction=>{
const data={} = a.payload.doc.data() as offer;
const id = a.payload.doc.id;
temp.push({id, ...data})
return data.bidderId
})
}),
switchMap(bidderIds=>{
// here you'll have all bidderIds and you need to return the array to query
// them to firebase
return combineLatest(bidderIds.map(bidderId=> return this.db.doc(bidderId)))
}),
map(bidders=>{
// here you'll get all bisders you'll have to set the bidder on each temp obj
// you saved previously
})
)
Make sure you import { combineLatest } from 'rxjs/operators' not 'rxjs'

Answer 2

I found a way. It is working. But I think it is bit big and there might be way to optimize it. Also it is node-js server API and not for the web (JS). Again there might be similar solution for the web (JS)
Once you get data from snapshot object there is _path key in the object returned by data which again have segments which is array and contain collection and ID
const gg = await firestore.collection('scrape').doc('x6F4nctCD').get();
console.log(JSON.stringify(gg.data(), null, 4));
console.log(gg.data().r._path.segments[0]);
console.log(gg.data().r._path.segments[1]);
const gg2 = await firestore
.collection(gg.data().r._path.segments[0])
.doc(gg.data().r._path.segments[1])
.get();
console.log(gg2.data());
{
"fv": {
"_seconds": 1578489994,
"_nanoseconds": 497000000
},
"tsnowpo": 1578489992,
"createdAt": {
"_seconds": 1578489992,
"_nanoseconds": 328000000
},
"r": {
"_firestore": {
"_settings": {
"libName": "gccl",
"libVersion": "3.1.0",
"servicePath": "firestore.googleapis.com",
"port": 443,
"clientConfig": {},
"scopes": [
"https://www.googleapis.com/auth/cloud-platform",
"https://www.googleapis.com/auth/datastore"
]
},
"_settingsFrozen": true,
"_serializer": {},
"_projectId": "sss",
"_lastSuccessfulRequest": 1578511337407,
"_preferTransactions": false,
"_clientPool": {
"concurrentOperationLimit": 100,
"activeClients": {},
"terminated": false
}
},
"_path": {
"segments": [
"egpo",
"TJTHMkxOx1C"
]
}
}
}
egpo
TJTHMkxOx1C
{ name: 'Homeware' }