NSFetchedResultsController sectionNameKeyPath不尊重fetchBatchSize

Question

对不起核心数据noob在这里......

我在NSFetchedResultsController上使用UITableViewController。实体中的数据包含timestamps。作为sectionID我想在节标题中使用日期。但是当我使用sectionNameKeyPath时，Core Data加载所有数据而不是尊重fetchBatchSize。

是我想要的，如果是的话，我在这里做错了什么。如果使用fetchedResultsController无法做到这一点，那有什么替代方案？

fetchedResultsController：

class func transactionsResultController(wallet: Wallet, batchSize: Int? = nil) -> NSFetchedResultsController<Transaction> {
    let appDelegate: AppDelegate = UIApplication.shared.delegate as! AppDelegate
    let context: NSManagedObjectContext = appDelegate.managedObjectContext

    let fetchedResultsController: NSFetchedResultsController = { () -> NSFetchedResultsController<Transaction> in
        let fetchRequest: NSFetchRequest<Transaction> = Transaction.fetchRequest()

        fetchRequest.predicate = NSPredicate(format: "ANY wallet == %@", wallet)

        fetchRequest.fetchBatchSize = batchSize ?? 20

        let sortDescriptor = NSSortDescriptor(key: #keyPath(Transaction.timestamp), ascending: false)
        fetchRequest.sortDescriptors = [sortDescriptor]

        let aFetchedResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: context, sectionNameKeyPath: "sectionIdentifier", cacheName: nil)

        do {
            try aFetchedResultsController.performFetch()
        } catch let error {
            debug(error)
        }
        return aFetchedResultsController
    }()

    return fetchedResultsController }

部分标识符：

extension Transaction{

var sectionIdentifier: String {
    let date = self.timestamp!.timestampToUTCDate(currency: (self.senderId?.currency!)!)
    let dateFormatter = DateFormatter()
    dateFormatter.timeZone = TimeZone(abbreviation: "en_US_POSIX")
    var components = DateComponents()
    let comps = Calendar.current.dateComponents([.year, .month, .day], from: date)
    components.day = comps.day
    components.month = comps.month
    components.year = comps.year
    let calendar = Calendar.current
    let reconstructedDate = calendar.date(from: components)!

    dateFormatter.dateFormat = "dd"
    let prettyDay = dateFormatter.string(from: reconstructedDate)
    dateFormatter.dateFormat = "MMMM"
    let prettyMonth = dateFormatter.string(from: reconstructedDate)
    dateFormatter.dateFormat = "YYYY"
    let prettyYear = dateFormatter.string(from: reconstructedDate)

    if (calendar.isDateInToday(reconstructedDate)){
        return "Today"
    }
    else if (calendar.isDateInYesterday(reconstructedDate)){
        return "Yesterday"
    }

    return "(prettyDay) (prettyMonth) (prettyYear)"
} }

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