本文介绍了Firebase在查询为空时的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述 29岁程序员，3月因学历无情被辞！ 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 这篇关于Firebase在查询为空时的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！ 上岸，阿里云！
