ParseUser.findInBackGround.result throws NullPointerException, even if the Query exists

[Berki2021]

Hello,

I am trying to search my user database for a specific key e.g. name here. The problem is that findInBackground throws a NullPointerException even if the user exists AND the specific key is found. Using find or first works but blocks the main thread.

Here is my code: fun checkNameExistsNullPointer(value: Any) = ParseUser.getQuery().whereEqualTo("username", "User1").findInBackground().result.isNullOrEmpty()

fun checkNameExistsWorksBlocking(value: Any) = !ParseUser.getQuery().whereEqualTo("username", "User1").find().isNullOrEmpty()

[Jawnnypoo]

That is because the bolts Task has not completed yet when you do findInBackground, therefore there is no result at the time that you are calling it. You would have to do something like findInBackground with a continuation to see the results. For example:

ParseUser.getQuery().whereEqualTo("username", "User1").findInBackground().continueWithTask { 
   if (it.result.isNullOrEmpty())
       doSomething()
   if (it.isFaulted()) 
       doSomethingForTheError()
}

[Berki2021]

fun checkNameExistsNullPointer(value: Any) {
    ParseUser.getQuery().whereEqualTo("username", "value").findInBackground().continueWithTask {
        return@continueWithTask it.result.isNullOrEmpty()
    }
}

Error:

Type mismatch. Required: ((Task<(Mutable)List<ParseUser!>!>!) → Task<(???..???)>!)! Found: (Task<(Mutable)List<ParseUser!>!>!) → Boolean

[Jawnnypoo]

You cannot return@continueWithTask the boolean, since it is expecting a Task. You'll want to read more about Bolts tasks and how they work here: https://github.com/BoltsFramework/Bolts-Android

[Berki2021]

Okay I will, but couldn't you provide me the answer?

EDIT: Ok, I got it:

` fun checkEmailExistsAsync(value: Any): Boolean {

    val result = ParseUser.getQuery().whereEqualTo("email", value).findInBackground().continueWith {
        return@continueWith it.result

    }.result

    return result.isNullOrEmpty()
} `

[Jawnnypoo]

This comment https://github.com/parse-community/Parse-SDK-Android/issues/1043#issuecomment-654349191 provides the answer you need. You cannot call async code, ie. a bolts task like this and expect it to return a synchronous result. You either need to change it to be fun checkEmailExistsAsync(value: Any): Task<Boolean> and transform the task from a list of users to the boolean you want, or you need to do the background threading yourself and use find instead of findInBackground.

[Berki2021]

Hmm okay, thanks.

[Berki2021]

@Jawnnypoo I have another question. Couldn't I write a cloud function which checks, if the email aka user already exists and call this cloud function asynchronously within android?

[Jawnnypoo]

Yes, that would be a good solution. Something like this:

            val params = mutableMapOf<String, Any>()
            params["email"] = value
            ParseCloud.callFunctionInBackground<Boolean>("checkEmailExists", params) {
                  doSomethingBasedOnResult()
            }

[Berki2021]

Amazing, thank you very much. Using a cloud function will give me the ability to call it from ios as well