Sleep thread until another thread completes for iOS - ios

Question

I'm very new to backend programming and iOS programming. I'm currently integrating DynamoDB into my iOS application. I'm doing a signup function that queries the database to check whether the username is taken.
Here's the main idea of my code:
__block BOOL isPlayerTaken = NO;
//Block of code that queries the database
//Mutates value of isPlayerTaken if player exists
[[dynamoDBObjectMapper query:[DDBRunnerTableRow class]
expression:queryExpression]
continueWithExecutor:[BFExecutor mainThreadExecutor] withSuccessBlock:^id(BFTask *task) {
AWSDynamoDBPaginatedOutput *paginatedOutput = task.result;
DDBRunnerTableRow *queriedRunner = paginatedOutput.items[0];
if (queriedRunner) {
isPlayerTaken = YES;
NSLog(#"%#", queriedRunner.runnerName);
}
return nil;
}];
return isPlayerTaken;
However, the function returns before the query result is completed and hence the output is always NO.
How can I ensure that the function doesn't return until the query block completes?
Thank you so much for your help. I believe I would need this in many functions of my code that requires querying and inserting of data and I didn't want to come up with a hackish solution for it.

Answer 1

Try something like this:
[[dynamoDBObjectMapper query:[DDBRunnerTableRow class]
expression:queryExpression]
continueWithExecutor:[BFExecutor mainThreadExecutor] withSuccessBlock:^id(BFTask *task) {
AWSDynamoDBPaginatedOutput *paginatedOutput = task.result;
DDBRunnerTableRow *queriedRunner = paginatedOutput.items[0];
if (queriedRunner)
{
NSLog(#"%#", queriedRunner.runnerName);
[self loginSuccessfull:queriedRunner];
}
else
{
[self loginFailed];
}
}];
then
- (void)loginSuccessfull:(DDBRunnerTableRow *)queriedRunner
{
//whatever
}
- (void)loginFailed
{
//whatever
}