ios - 删除核心数据项

Question

我怎样才能删除实体中特定属性中的所有数据我不想清空实体中的所有属性这是我现在拥有的删除实体中所有属性的方法

 func deletObject(){
    let fetchRequest = NSFetchRequest()
    let appDel:AppDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
    fetchRequest.includesPropertyValues = false
    let context:NSManagedObjectContext = appDel.managedObjectContext
    let moc = context
    fetchRequest.entity = NSEntityDescription.entityForName("Cart", inManagedObjectContext: moc)

    do {
        if let results = try moc.executeFetchRequest(fetchRequest) as? [NSManagedObject] {
            for result in results {
                moc.deleteObject(result)
            }
            try moc.save()
            self.cart = [Cart]()
            self.tableView.reloadData()
            totalAmouLa.text = "₦\(Int(totalHoursWorkedSum))"
        }
    } catch {
        print("FAILED")
    }

}

编辑我想删除 Cart 实体中的 delivery Image

Answer 1

您不能从 Core Data 模型中删除一个属性，您只能重置该值。

executeFetchRequest 成功返回保证[Cart]，可选绑定(bind)永远不会失败

func deletObject(){
    let fetchRequest = NSFetchRequest()
    let appDel  = UIApplication.sharedApplication().delegate as! AppDelegate
    let context = appDel.managedObjectContext
    fetchRequest.entity = NSEntityDescription.entityForName("Cart", inManagedObjectContext: context)

    do {
        let results = try context.executeFetchRequest(fetchRequest) as! [Cart]
        results.forEach { $0.delivery = 0.0 }
        try context.save()
        self.tableView.reloadData()
        totalAmouLa.text = "₦\(Int(totalHoursWorkedSum))"
    } catch {
        print("FAILED")
    }
}