RecordFetchedBlock on CKQueryOperation not being called

I need to request records of type "Event" for CKRecords. When I call recordFetchedBlock, I will add these records to my array. However, recordFetchedBlock will never be called. Please help! Thank:

    //TODO: Query for all Event records
    var database: CKDatabase = CKContainer.defaultContainer().privateCloudDatabase

    let truePredicate = NSPredicate(value: true)
    let eventQuery = CKQuery(recordType: "Event", predicate: truePredicate)

    let queryOperation = CKQueryOperation(query: eventQuery)

    queryOperation.recordFetchedBlock = { (record : CKRecord!) in

            self.eventsArray.append(record)
            println("recordFetchedBlock: \(self.eventsArray)")
    }

    queryOperation.queryCompletionBlock = { (cursor : CKQueryCursor!, error : NSError!) in

        println("queryCompletionBlock: \(self.eventsArray)")
    }

    database.addOperation(queryOperation)