如何获取 Firestore 集合中所有文档的子集合的特定文档？

Question

So, I have my data ordered in this way:

MyCollection                  //main collection       
  --(All documents)           //I want all documents of main collection
     --publicSubcollection    //I want ONLY publicSubcollection of those documents
        --(All documents)     //I want all documents of publicSubcollection

And here is how I am doing it in my app:

 query = firestore().collection('MyCollection').doc().collection('publicSubcollection')
                .where('act', '==', 1)
                .where('city', '==', this.state.selected_city)
                .orderBy('update_time', 'desc')
                .limit(10);

            query.onSnapshot({
                 //do something
           })

and it is returning nothing, empty object. I tried calling REST Api using Postman and it also returns empty object. I tried by calling only 'MyCollection' and it returns some data I have in there. So, how can I actually query documents in a specific sub-collection? What am I doing wrong in this code?

Answer 1

It never makes sense to use doc() without an argument in a Firestore query. Without an argument, it generates a DocumentReference with a random document ID. That ID will certainly not exist, and your query will not return any results. If you want to query a subcollection, you need to be able to build a path to that subcollection, including all document IDs in that path. There are no wildcard matches in Firestore paths. In other words, you need to pass a string to doc() that identifies which document's subcollection to query. That document doesn't need to exist - it just needs to be named.

If you are actually trying to query all documents in all subcollections called "publicSubcollection", you'll need to use a collection group query instead. It might looks like this:

query = firestore()
    .collectionGroup('publicSubcollection')
    .where('act', '==', 1)
    .where('city', '==', this.state.selected_city)
    .orderBy('update_time', 'desc')
    .limit(10);