How to safely handle multiple writes in firebase which must all happen - ios

Question

I want to handle a friend request in my app written in Swift using Firebase. In my database, this means that the user sending the request needs to add the other user to their "sentRequests" dictionary, and the user receiving the request needs to add the user sending the requests to their "receivedRequests" dictionary. The problem is, if the user sending the request has a faulty connection and only does the first part, then it might cause issues. Either both writes should happen or none. What can I do to fix this? I included my code below for reference, but honestly if someone just sends me a good tutorial or answer here that would be just has helpful as correctly rewriting my code.
static func sendRequestFromCurrentUser(toUser userThatRequestWasSentTo : User, succeeded : #escaping (Bool)->Void ){
let ref = Database.database().reference().child("users").child(User.current.uid).child("sentRequests").child(userThatRequestWasSentTo.uid)
ref.setValue(userThatRequestWasSentTo.toDictionary(), withCompletionBlock: {(error, ref) in
if error == nil{
let currentUserRef = Database.database().reference().child("users").child(userThatRequestWasSentTo.uid).child("receivedRequests").child(User.current.uid)
currentUserRef.setValue(User.current.toDictionary(), withCompletionBlock: {(error, ref) in
if error == nil{
succeeded(true)
}
else{
succeeded(false)
}
})
}
else{
succeeded(false)
}
})
}

Answer 1

So I stole this from the Firebase blog and got it to match my code. The answer is fairly intuitive, I just hadn't considered it. Basically you just create a reference to the top level of your database and specify the paths you want to write to in the dictionary (so not by creating specific references with child()), and then just call updateChildValues().
static func sendRequestFromCurrentUser(toUser userThatRequestWasSentTo : User, succeeded : #escaping (Bool)->Void ){
let ref = Database.database().reference()
// Create the data we want to update
var updatedUserData : [String : Any] = [:]
updatedUserData["users/\(User.current.uid)/sentRequests/\(userThatRequestWasSentTo.uid)"] = userThatRequestWasSentTo.toDictionary()
updatedUserData["users/\(userThatRequestWasSentTo.uid)/receivedRequests/\(User.current.uid)"] = User.current.toDictionary()
// Do a deep-path update
ref.updateChildValues(updatedUserData, withCompletionBlock: { (error, ref) in
if let error = error {
print("Error updating data: \(error.localizedDescription)")
succeeded(false)
}
else{
succeeded(true)
}
})
}