Firestore query subcollections

Question

I thought I read that you can query subcollections with the new Firebase Firestore, but I don\'t see any examples. For example I have my Firestore setup in the following way

Answer 1

What if you store songs as an object instead of as a collection? Each dance as, with songs as a field: type Object (not a collection)

{
  danceName: "My Dance",
  songs: {
    "aNameOfASong": true,
    "aNameOfAnotherSong": true,
  }
}

then you could query for all dances with aNameOfASong:

db.collection('Dances')
  .where('songs.aNameOfASong', '==', true)
  .get()
  .then(function(querySnapshot) {
    querySnapshot.forEach(function(doc) {
      console.log(doc.id, " => ", doc.data());
    });
   })
   .catch(function(error) {
     console.log("Error getting documents: ", error);
    });

Answer 2

NEW UPDATE July 8, 2019:

db.collectionGroup('Songs')
  .where('songName', isEqualTo:'X')
  .get()

Answer 3

Query limitations

Cloud Firestore does not support the following types of queries:

1. Queries with range filters on different fields.

2. Single queries across multiple collections or subcollections. Each query runs against a single collection of documents. For more information about how your data structure affects your queries, see Choose a Data Structure.

3. Logical OR queries. In this case, you should create a separate query for each OR condition and merge the query results in your app.

4. Queries with a != clause. In this case, you should split the query into a greater-than query and a less-than query. For example, although the query clause where("age", "!=", "30") is not supported, you can get the same result set by combining two queries, one with the clause where("age", "<", "30") and one with the clause where("age", ">", 30).

Answer 4

Update 2019-05-07

Today we released collection group queries, and these allow you to query across subcollections.

So, for example in the web SDK:

db.collectionGroup('Songs')
  .where('songName', '==', 'X')
  .get()

This would match documents in any collection where the last part of the collection path is 'Songs'.

Your original question was about finding dances where songName == 'X', and this still isn't possible directly, however, for each Song that matched you can load its parent.

Original answer

This is a feature which does not yet exist. It's called a "collection group query" and would allow you query all songs regardless of which dance contained them. This is something we intend to support but don't have a concrete timeline on when it's coming.

The alternative structure at this point is to make songs a top-level collection and make which dance the song is a part of a property of the song.

Answer 5

UPDATE Now Firestore supports array-contains

Having these documents

    {danceName: 'Danca name 1', songName: ['Title1','Title2']}
    {danceName: 'Danca name 2', songName: ['Title3']}

do it this way

collection("Dances")
    .where("songName", "array-contains", "Title1")
    .get()...

---

@Nelson.b.austin Since firestore does not have that yet, I suggest you to have a flat structure, meaning:

Dances = {
    danceName: 'Dance name 1',
    songName_Title1: true,
    songName_Title2: true,
    songName_Title3: false
}

Having it in that way, you can get it done:

var songTitle = 'Title1';
var dances = db.collection("Dances");
var query = dances.where("songName_"+songTitle, "==", true);

I hope this helps.