ios - Retrieve only one value(forKey: ) from Firebase Database -

right have used breakpoint check value @ each step of method. print statement works know going through. value of newannotationsubtitle "1 cupertino ca, us" , want check if annotationsubtitle in database same. let existingannotationsubtitle returns nil know there value. can't seem access key: value. can change?

for reference, placemarkname = "apple infinite loop"

let annotationref = database.database().reference(withpath: "annotationitems")  annotationref.observesingleevent(of: .value, with: { snapshot in     print("it works")     if snapshot.haschild(placemarkname!) {        let newannotationsubtitle: string = preannotationlistitem.preannotationsubtitle        let existingannotationsubtitle = snapshot.childsnapshot(forpath: placemarkname!).value(forkey: "annotationsubtitle")! as? string     } 

my json looks

"annotationitems" : {    "apple infinite loop" : {      "annotationsubtitle" : "1 cupertino ca, us",    } }