Firebase在查询为空时 [英] Firebase when query is empty

问题描述

我使用firebase执行查询来检查是否有任何具有特定值的子对象。问题是如果没有这样的对象代码不运行。所以在下面的代码中，如果没有包含 facebookID 的子元素 17 ，那么剩下的代码永远不会运行。有没有一种方法来确定查询何时发现 0 结果？

  func previousUser（completion：（result：Bool） - > Void）{
 
 var queryFound = false 
 print（check if user is previous）
 print（UserData。 globalfacebookID）
 let ref = Firebase（url：https://amber-torch-556.firebaseio.com/Users）
 ref.queryOrderedByChild（facebookID）。queryEqualToValue（17）.observeSingleEventOfType （.ChildAdded，withBlock：{snapshot in 
 
 print（snapshot.childrenCount）
 print（query has ran）
 UserData.globalparseID = snapshot.key 
 
 queryFound = true 
 completion（result：queryFound）
 $ b $）
  

<

试试这个

  ref.queryOrderedByChild（facebookID）。queryEqualToValue（17）
 .observeEventType（.Value，withBlock：{snapshot in 
 
如果snapshot.value是NSNull {
 print（dude，snapshot was null）
} else {
 print（snapshot.key）
 } 
 
 
 
 
 
 
 
将.ChildAdded更改为.Value，然后检查NSNull 
 
I perform a query using firebase to check if there are any objects that have a child with a certain value. The problem is if there are no such objects the code doesn't run. So in the code below if there are no objects that have a child with facebookID that is 17 the rest of the code will never run. Is there a way to determine when a query finds 0 results?
func previousUser(completion:(result:Bool)->Void){

    var queryFound = false
    print("check if user is previous")
    print(UserData.globalfacebookID)
    let ref = Firebase(url:"https://amber-torch-556.firebaseio.com/Users")
    ref.queryOrderedByChild("facebookID").queryEqualToValue(17).observeSingleEventOfType(.ChildAdded, withBlock: { snapshot in

    print(snapshot.childrenCount)
    print("query has ran")
    UserData.globalparseID = snapshot.key

    queryFound = true
    completion(result:queryFound)

})

解决方案
Check your ref to make sure it's valid.

and try this
        ref.queryOrderedByChild("facebookID").queryEqualToValue(17)
           .observeEventType(.Value, withBlock: { snapshot in

              if snapshot.value is NSNull {
                 print("dude, snapshot was null")
              } else {
                 print(snapshot.key)
              }

        })
Change .ChildAdded to .Value and then check for NSNull

                        
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