Public cloud database query doesn't return nil when it should

Question

I want to check for the existence of a record with a certain predicate and, if it doesn't exist, do something:

let publicDatabase = CKContainer.default().publicCloudDatabase
let predicate: NSPredicate!
predicate = NSPredicate(format: "username == %@", usernameText)
let query =  CKQuery(recordType: "user", predicate: predicate)
let configuration = CKQueryOperation.Configuration()
configuration.allowsCellularAccess = true
configuration.qualityOfService = .userInitiated

let queryOperation = CKQueryOperation(query: query)
queryOperation.desiredKeys = ["username"]
queryOperation.queuePriority = .veryHigh
queryOperation.configuration = configuration
queryOperation.resultsLimit = 1
queryOperation.recordFetchedBlock = { (record: CKRecord?) -> Void in
    if let record = record {
    // #1
        print("record \(record)")
    } else {
    // #2
        print("none exists")
    }
}

queryOperation.queryCompletionBlock = { (cursor: CKQueryOperation.Cursor?, error: Error?) -> Void in
    if let error = error {
        print("\(error)")
        return
    }
    
    if let cursor = cursor {
        print("cursor: \(cursor)")
    }
}

publicDatabase.add(queryOperation)

When a record matching the predicate exists, the record is returned as it should, but when it doesn't exist, not even nil gets returned for me to react accordingly. What I mean is ideally I want to execute my code in #2 in response to the nonexistence of any records, but recordFetchedBlock doesn't seem to run in that case.

Steve B · Accepted Answer · 2020-10-07 07:46:47Z

The issue here is recordFetchedBlock is only called when you get a record. No record? Then it won't be called. The below approach should do the trick for you:

//define an array to store all records
var allRecords = []

queryOperation.recordFetchedBlock = { record in
    //called once for each record
    //if no results, then it is never called
    //if you get a record, add to the array
    allRecords.append[record]
}

//the query completion block is called at the end of the query (or when all results can't be returned in one block, then called with non-nil cursor value.  Considering that out of scope for this answer.
queryOperation.queryCompletionBlock = { (cursor: CKQueryOperation.Cursor?, error: Error?) in
    if let error = error {
        //handle error
    }
    if let cursor = cursor {
       //handle cursor if exists    
    } 
    if allRecords.count == 0 {
        //my query returned no results
        //take desired action    
    }
}

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