Checking if Firebase snapshot is equal to nil in Swift

Question

I am trying to query Firebase to check if any user that has waiting: \"1\" and then when the snapshot is returned I want to see whether it is equal to nil. I ha

Answer 1

Check for NSNull. This is the code for observing a node. Queries work much the same way.

Here's a complete and tested app. To use, change the string 'existing' to some path you know exists, like your users path and the 'notexisting' to some path that does not exist

    let myRootRef = Firebase(url:"https://your-app.firebaseio.com")
    let existingRef = myRootRef.childByAppendingPath("existing")
    let notExistingRef = myRootRef.childByAppendingPath("notexisting")

    existingRef.observeEventType(.Value, withBlock: { snapshot in

        if snapshot.value is NSNull {
            print("This path was null!")
        } else {
            print("This path exists")
        }

    })

    notExistingRef.observeEventType(.Value, withBlock: { snapshot in

        if snapshot.value is NSNull {
            print("This path was null!")
        } else {
            print("This path exists")
        }

    })

Please note that by using .Value, there will be a guaranteed a return result and the block will always fire. If your code used .ChildAdded then the block will only fire when a child exists.

Also, check to make sure of how your data appears in firebase.

users
   user_0
     waiting: 1

if different than

users
   user_0
     waiting: "1"

Note that "1" is not the same as 1.

Answer 2

There are a few things going on here, but the most important one is that you cannot test for the existence of children with .ChildAdded. That makes sense if you think about it: the .ChildAdded event is raised when a child is added to the location. If no child is added, the event won't be raised.

So if you want to test if a child exists at a location, you need to use .Value. Once you do that, there are various way to detect existence. Here's one:

ref.queryOrderedByChild("waiting").queryEqualToValue("1")
   .observeEventType(.Value, withBlock: { snapshot in
       print(snapshot.value)
       if !snapshot.exists() {
           print("test2")
       }
   });