java Firebase数据库高级查询选项

Question

我的数据结构如下。本质上，我创建了一个“关注者”类别，作为每个键的子键，其中一个键代表一次投票。如果我的应用程序的当前用户ID列在“关注者”类别中，我希望该节点与我的查询相关。否则，我希望它被忽略

这种类型的查询可能吗？我从我的顶层“Polls”开始，然后我必须遍历每个子键，然后在该键中遍历“Following”子键：

    Query query = FirebaseDatabase.getInstance()
            .getReference()
            .child("Polls");

Answer 1

这种查询是可能的

您只需要查看每个轮询对象，看看您要查找的用户ID是否存在于关注者列表中

另一个解决方案是保留一个Followers节点，该节点根据用户ID将关注者链接到他们关注的投票

下面将对此进行更详细的描述：

https://firebase.google.com/docs/database/android/structure-data#flatten_data_structures

如果数据被分割成单独的路径（也称为非规范化），则可以根据需要在单独的调用中高效下载数据。考虑这个扁平结构：

{
  // Chats contains only meta info about each conversation
  // stored under the chats's unique ID
  "chats": {
    "one": {
      "title": "Historical Tech Pioneers",
      "lastMessage": "ghopper: Relay malfunction found. Cause: moth.",
      "timestamp": 1459361875666
    },
    "two": { ... },
    "three": { ... }
  },

  // Conversation members are easily accessible
  // and stored by chat conversation ID
  "members": {
    // we'll talk about indices like this below
    "one": {
      "ghopper": true,
      "alovelace": true,
      "eclarke": true
    },
    "two": { ... },
    "three": { ... }
  },

  // Messages are separate from data we may want to iterate quickly
  // but still easily paginated and queried, and organized by chat
  // conversation ID
  "messages": {
    "one": {
      "m1": {
        "name": "eclarke",
        "message": "The relay seems to be malfunctioning.",
        "timestamp": 1459361875337
      },
      "m2": { ... },
      "m3": { ... }
    },
    "two": { ... },
    "three": { ... }
  }
}