如何使用Android在Cloud Firestore中查詢特定文檔后的集合？

Question

我具有以下數據庫結構：

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

使用這種數據庫結構，我可以簡單地查詢與特定用戶相對應的所有列表。 但是，如何查詢數據庫以獲取具有特定列表的所有用戶？

在這種情況下，如何獲取所有具有ListOne作為列表的用戶？ 結果應為： userId1

我需要重復數據還是有另一種方法？

編輯：

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

謝謝！

Answer 1

無法將查詢擴展到多個子集合。 查詢必須包含在單個集合或子集合中。 因此，您猜測需要重復數據才能執行查詢是正確的。

Answer 2

實際上有一個技巧可以完成。 您可以在docKey1文檔中添加map ，而不是復制數據，如Todd Kerpelman 在此處所述。 您的文檔如下所示：

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

因此，您可以查詢該特定文檔以獲取所有用戶ID。 因此，您可以通過這種方式獲得所需的信息。