swift - 如何使用 BETWEEN 子句创建 CoreData SUBQUERY？

Question

我试图仅检索其 entries.date 在两个日期之间的类别。我的研究表明，这可以通过 SUBQUERY 实现。我遵循了这篇 medium.com 文章中的示例 SUBQUERY Is Not That Scary然而，当我运行我的项目时，我得到一个 'NSInvalidArgumentException'，原因:'无法解析格式字符串“SUBQUERY(entries, $entry, $entry.date BETWEEN {%@, %@})”'

我已经上传了我的数据模型的图像和我的 NSFetchedResultsController 内容的代码片段，我在其中使用 SUBQUERY 构造了我的谓词语句。

Image of my data model

    // Create Fetch Request
    let fetchRequest: NSFetchRequest<CDCategory> = CDCategory.fetchRequest()

    // Configure Fetch Request
    fetchRequest.sortDescriptors = [NSSortDescriptor(key: "entriesCount", ascending: false)]
    fetchRequest.predicate = NSPredicate(format: "SUBQUERY(entries, $entry, $entry.date BETWEEN {%@, %@})", dataController.week.startDate as CVarArg, dataController.week.endDate as CVarArg)

    // Create Fetched Results Controller
    let fetchedResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: CoreDataStack.instance.context, sectionNameKeyPath: nil, cacheName: nil)

    // Configure Fetched Results Controller
    fetchedResultsController.delegate = self

    return fetchedResultsController

Answer 1

您需要向子查询添加一个条件:假设您想要包含 CDCategory 对象，其中任何一个 entries 的日期都在您的两个给定日期之间，您希望子查询的计数大于零:

fetchRequest.predicate = NSPredicate(format: "SUBQUERY(entries, $entry, $entry.date BETWEEN {%@, %@}).@count > 0", dataController.week.startDate as CVarArg, dataController.week.endDate as CVarArg)

相反，如果您只想选择那些没有条目日期匹配的条目，您希望计数为零:

fetchRequest.predicate = NSPredicate(format: "SUBQUERY(entries, $entry, $entry.date BETWEEN {%@, %@}).@count == 0", dataController.week.startDate as CVarArg, dataController.week.endDate as CVarArg)

类似的结构将允许您只选择所有条目都符合您的条件的结构。