结果数量计算: resultType

  1. let fetchRequest = 
  2.  NSFetchRequest<NSNumber>(entityName: "Venue")
  3.  fetchRequest.resultType = .countResultType
  4.  fetchRequest.predicate = moderateVenuePredicate
  5.  do {
  7.  let countResult = 
  8.  try coreDataStack.managedContext.fetch(fetchRequest)
  9.  let count = countResult.first?.intValue ?? 0
  10.  let pluralized = count == 1 ? "place" : "places"
  11.  secondPriceCategoryLabel.text = 
  12.  "\(count) bubble tea \(pluralized)"
  1. lazy var expensiveVenuePredicate: NSPredicate = {
  2.  return NSPredicate(format: "%K == %@", 
  3.  #keyPath(Venue.priceInfo.priceCategory), "$$$")
  4. }()
  6. func populateExpensiveVenueCountLabel() {
  7.  let fetchRequest: NSFetchRequest<Venue> = Venue.fetchRequest()
  8.  fetchRequest.predicate = expensiveVenuePredicate
  9.  do {
  10.  let count =
  11.  try coreDataStack.managedContext.count(for: fetchRequest)
  12.  let pluralized = count == 1 ? "place" : "places"
  13.  thirdPriceCategoryLabel.text = 
  14.  "\(count) bubble tea \(pluralized)"
  15.  } catch let error as NSError {
  16.  print("count not fetched \(error), \(error.userInfo)")
  17.  }
  18. }

结果内字段数量总和 dictionaryResultType.

NSManagedObjectID 替代UID?

增加限制，否则获得的是所有的数据，存储到内存中

NSSortDescriptor

NSPredicate

NSAsynchronousFetchRequest

NSBatchUpdateRequest ：所有邮件已读

NSBatchDeleteRequest：Delete all