Firebase QueryOrderedByChild以及EqualToValue和StartingAtValue组合 [英] Firebase QueryOrderedByChild along with EqualToValue and StartingAtValue Combination

问题描述

我试图通过一个等于某个特定值的子查询Firebase，但是在特定的发布键上启动快照。

数据结构：

  projectName 
 -posts 
 -postKey1 
 -storeId：1 
 -postKey2 
 -storeId：2 
 -postKey3 
 -storeId：3 
 -postKey4 
 -storeId：2 
 -postKey5 
 -storeId：3 
 -postKey6 
 -storeId：2 
  

示例：

我试图用<$ c $ queryOrderedByChild（storeId） c> queryEqualToValue（2）但是我希望快照在按照顺序返回的时候从postKey4开始。

我当前的查询：
$ b

  ref.queryOrderedByChild（storeId）。q​​ueryEqualToValue（\我知道你可以通过这个方法来创建一个新的表单。在 queryStartingAtValue ， queryEndingAtValue 或<$之后调用 queryEqualToValue： c $ c> queryEqualToValue 之前被调用，但我需要 queryEqualToValue 来获得我的storeId。您可以将第二个参数传递给 queryStartingAtValue   c $> b 
 $ b $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ b $ 2，childKey：postKey4）
 .queryEndingAtValue（2）
 .observeEventType（.Value，withBlock：{快照在
中用于snapshot.children中的childSnapshot {
 print（childSnapshot .key !! 
} 
}）
  

打印：

postKey4

postKey6

我必须承认这是我第一次使用第二个参数到 queryStartingAtValue ，所以我可能还不完全理解它。

你不能使用 queryEqualToValue 的原因是它只会返回一个单一的键，这不是你想要的。

I am trying to query Firebase by a Child that is equal to a certain value BUT start the snapshot at a specific post key.

Data Structure:

projectName
  -posts
    -postKey1
      -storeId: 1
    -postKey2
       -storeId: 2
    -postKey3
       -storeId:3
    -postKey4
       -storeId:2
    -postKey5
       -storeId:3
    -postKey6
       -storeId:2

Example:

I am trying to queryOrderedByChild("storeId") with queryEqualToValue("2") BUT I would like the snapshot to start at "postKey4" when it is returned in its order.

My Current Query:

ref.queryOrderedByChild("storeId").queryEqualToValue("\(myId)").observeEventType(.Value, withBlock: {snapshot in 

I know that you can't call queryEqualToValue: after queryStartingAtValue, queryEndingAtValue or queryEqualToValue after previously called but I need that queryEqualToValue to get my storeId. Any help is greatly appreciated!

解决方案

You can pass a second argument into queryStartingAtValue that specifies the key at which to start.

ref.queryOrderedByChild("storeId")
   .queryStartingAtValue(2, childKey: "postKey4")
   .queryEndingAtValue(2)
   .observeEventType(.Value, withBlock: {snapshot in
       for childSnapshot in snapshot.children {
           print(childSnapshot.key!!
       }
})

This prints:

postKey4

postKey6

I must admit this is the first time I use the second argument to queryStartingAtValue, so I might not understand it completely yet.

The reason you can't use queryEqualToValue is that that will only return a single key, which is not what you want.

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