Firestore: Get subcollection of document found with where

Question

I am trying to get the documents inside an subcollection which is part of an document found with the .where function

Example:

• RootColl/
• Doc A/
  • SubColl 1
    • Doc 1
    • Doc 2
    • Doc 3
  • SubColl 2
    • Docs
• Doc A/
  • SubColl 1
    • Doc 1
    • Doc 2
    • Doc 3
  • SubColl 2
    • Docs

I want to get all the documents under SubColl 1 from the doc with the field level == 1

I am trying to do it like:

db.collection("RootColl").where("field", "==", "1").collection("SubColl 1").get()

But by doing that I get the error

Uncaught TypeError: db.collection(...).where(...).collection is not a function

EDIT 1: By following Frank van Puffelen suggestion, i get the same error, "collection" is not a function

• Current Code
• Error

Answer 1

A sub-collection lives under a specific document. A query as you've shared now points to a number of documents. You'll need to execute the query to determine what documents it points to, then loop over the results, and get the sub-collection for each document.

In code:

var query = db.collection("RootColl").where("field", "==", "1");
query.get().then((querySnapshot) => {
  querySnapshot.forEach((document) => {
    document.ref.collection("SubColl 1").get().then((querySnapshot) => {
      ...
    });
  });
});

Answer 2

With Firebase Version 9 (Sep, 2021 Update):

If subcollection(subcoll) contains 3 documents(doc1, doc2, doc3) like below:

coll > doc > subcoll > doc1 > field1: "value1", field2: "value2"
                       doc2 > field1: "value1", field2: "value2"
                       doc3 > field1: "v1",     field2: "v2"

You can get 2 documents(doc1, doc2) of subcollection(subcoll) with while below:

import { query, collection, where, getDocs } from "firebase/firestore";

const q = query(collection(db, "coll/doc/subcoll"), 
                where("field1", "==", "value1"));
    
const docsSnap = await getDocs(q);

docsSnap.forEach((doc) => {
  console.log(doc.data()); // "doc1" and "doc2"
});

Without forEach() method to get 2 documents(doc1, doc2) of subcollection(subcoll) with while below:

import { query, collection, where, getDocs } from "firebase/firestore";

const q = query(collection(db, "coll/doc/subcoll"),
                where("field1", "==", "value1"));
    
const docsSnap = await getDocs(q);
    
console.log(docsSnap.docs[0].data()); // "doc1"
console.log(docsSnap.docs[1].data()); // "doc2"

In addition, you can get all 3 documents(doc1, doc2, doc3) of subcollection(subcoll) with the code below:

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

const docsSnap = await getDocs(collection(db,"coll/doc/subcoll"));
      
docsSnap.forEach((doc) => {
  console.log(doc.data()); // "doc1", "doc2" and "doc3"
});

Without forEach() method to get all 3 documents(doc1, doc2, doc3) of subcollection(subcoll) below:

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

const docsSnap = await getDocs(collection(db, "coll/doc/subcoll"));
        
console.log(docsSnap.docs[0].data()); // "doc1"
console.log(docsSnap.docs[1].data()); // "doc2"
console.log(docsSnap.docs[2].data()); // "doc3"

Again, in addition, you can get only one specific document(doc3) of subcollection(subcoll) with the code below:

import { getDoc, doc } from "firebase/firestore";

const docSnap = await getDoc(doc(db, "coll/doc/subcoll/doc3"));
          
console.log(docSnap.data()); // "doc3"