Firebase：在javascript事件中查询过滤 [英] Firebase: Query filtering in javascript on() events

问题描述

有没有一种方法来过滤每个孩子的属性，我想带回ref.on（价值，...）？假设我有 https://www.firebase.com/docs/data-structure.html ，但是除了名称之外，每个用户还有他生产的每一个聊天列表。如何才能取回名称？

解决方案

更新：从Firebase 2.0开始，现在根据字段查询。

目前还没有办法从路径中选择数据（即过滤返回的字段）。最简单的解决方案是将数据存储在不同的路径中。这大大简化了这个过程。

 用户/ 
用户/名称/ fred /第一个
个用户/ chat_history / fred / ... 
  

另一个有用的方法，特别是当你要使用很多的子集（例如朋友列表，组的成员等）将使用索引。

  user_index / group_1 / fred 
 user_index / group_1 / mary 
 user_index / group_2 / ... 
 
 users / fred / name 
 users / fred / chat_history 
  
 $ b $ p 
 $ b 
然后你可以像这样访问数据： 
 
 
  var fb = new Firebase（INSTANCE）; 
 fb.child（'user_index'）。on（'child_added'，function（ss）{
 fb.child（'users /'+ ss.name（）+'/ name'）。once （'value'，function（nameSnapshot）{
 var userName = nameSnapshot.val（）; 
}）; 
}）; 
  
 
Is there a way to filter down which properties of each child I want to bring back inside of ref.on("value", ...)? 


Let's say I have the structure on https://www.firebase.com/docs/data-structure.html, but in addition to name, each user also has a list of every line of chat he has produced. How can I bring back only the name?
解决方案
UPDATE: As of Firebase 2.0, you can now query based on fields.

There isn't currently a way to pick data out of a path (i.e. filter which fields you get back). The easiest solution here is to store the data in different paths. It greatly simplifies the process.
users/
users/names/fred/first
users/chat_history/fred/...
Another useful approach, particularly when you're going to be using a lot of subsets (e.g. friends list, members of a group, et al) is to use an index.
user_index/group_1/fred
user_index/group_1/mary
user_index/group_2/...

users/fred/name
users/fred/chat_history
Then you can access the data with something like this:
var fb = new Firebase(INSTANCE);
fb.child('user_index').on('child_added', function(ss) {
   fb.child('users/'+ss.name()+'/name').once('value', function(nameSnapshot) {
      var userName = nameSnapshot.val();
   });
});


                        
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