CODEWITHSUNDEEP
javaandroidfirebasegoogle-cloud-firestore
Always Learner
Always Learner

Reputation: 2962

How to query a Collection after a specific Document in Cloud Firestore with Android?

I have the following database structure:

Firestore-root
    |
    --- lists (collection)
          |
          --- userId1 (document)
          |     |
          |     --- userLists (collection)
          |             |
          |             --- docKey1 (document)
          |             |     |
          |             |     --- listName: "ListOne"
          |             |     |
          |             |     --- date: January 15, 2018 at 9:56:24 AM UTC+2
          |             |
          |             --- docKey2 (document)
          |                   |
          |                   --- listName: "ListTwo"
          |                   |
          |                   --- date: January 15, 2018 at 9:58:12 AM UTC+2
          |
          --- userId2 (document)
                |
                --- userLists (collection)
                        |
                        --- docKey1 (document)
                        |     |
                        |     --- listName: "ListOne"
                        |     |
                        |     --- date: January 15, 2018 at 9:56:24 AM UTC+2
                        |
                        --- docKey3 (document)
                              |
                              --- listName: "ListThree"
                              |
                              --- date: January 15, 2018 at 9:59:47 AM UTC+2

Using this database structure, I can simply query all lists that correspond to a specific user. But, how can I query the database to get all the users that have a specific list?

In this particular case, how to get all the users that have ListOne as a list? The result should be: userId1

Do I need to duplicate data or is there another way for doing this?

Edit:

Firestore-root
    |
    --- allList
           |
           --- listId1 (collection)
                  |
                  --- userId1 (document)
                  |      |
                  |      --- username: "FirstUser"
                  |      |
                  |      --- //other details
                  |
                  --- userId2 (document)
                         |
                         --- username: "SecondUser"
                         |
                         --- //other details

Thanks!

Upvotes: 1

Views: 543

Answers (2)

Alex Mamo
Alex Mamo

Reputation: 138824

There actually a trick that can be done. Instead of duplicating data, you can add in your docKey1 document a map, as Todd Kerpelman said here. Your document whould look like this:

userLists (collection)
    |
    --- docKey1 (document)
          |
          --- listName: "ListOne"
          |
          --- date: January 15, 2018 at 9:56:24 AM UTC+2
          |
          --- users
               |
               --- userId1: true
               |
               --- userId2: true

So you can query that particular document to get all the user ids. So in this way you can get a sort what you are asking for.

Upvotes: 0

Doug Stevenson
Doug Stevenson

Reputation: 317467

There's no way to extend a query across multiple subcollections. A query must be contained within a single collection or subcollection. So, you're correct in guessing that you'll need to duplicate data in order to perform your query.

Upvotes: 2

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