以编程方式更改核心数据文件中的数据

Question

大家好，提前谢谢！

我是核心数据的菜鸟，我需要在我的一个字段中更改数据，其名称为：recid。

我创建了一个索引，它又是：在我的核心数据模型中recid为int 16。

我需要做的是获取记录并更改recid，我们会说5比1我将如何做到这一点？

这是我到目前为止构建的代码，在了解如何更改记录中的数据后，我将处理我的循环。

-(void)awakeFromNib
{
    NSMenu *theMenu;
    statusItem = [[[NSStatusBar systemStatusBar] statusItemWithLength:NSVariableStatusItemLength] retain];
    [statusItem setMenu:statusMenu];
    [statusItem setImage:[NSImage imageNamed:@"TheJournal_16x16x32"]];
    [statusItem setHighlightMode:YES];
    theMenu = [[NSMenu alloc] initWithTitle:@""];
    [theMenu addItemWithTitle:@"The Journal" action:@selector(showTheWindow:) keyEquivalent:@"W"];
    [theMenu addItemWithTitle:@"Quit" action:@selector(terminate:) keyEquivalent:@"Q"];
    [statusItem setMenu:theMenu];
    [theMenu release];

    NSUInteger count;
    count = 0;
    NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults];
    count = [prefs integerForKey:@"recid"];
    NSLog(@"counter is >>>>%lu",(unsigned long)count);
    [prefs setInteger:count forKey:@"recid"];
    count++;
    NSUserDefaults *prefs1 = [NSUserDefaults standardUserDefaults];
    [prefs1 setInteger:count forKey:@"recid"];
    NSLog(@"counter is >>>>%lu",(unsigned long)count);

    // How I fetch the record & change the value from 5 to 1?
}

Answer 1

这是一个可能对您有帮助的代码示例。在此示例中，YourManagedClass核心数据实体使用UUID字符串作为唯一记录标识符。扩展包含一个静态函数，用于获取唯一记录，设置新的recid值，然后保存NSManagedObjectContext。

import Foundation
import CoreData

class YourManagedClass: NSManagedObject {
    @NSManaged var uuid: String?
    @NSManaged var recid: NSNumber?
}

extension YourManagedClass {
    static func set(recID: Int16, forObject uuid: String, `in` context:     NSManagedObjectContext) {
        let fetchRequest = NSFetchRequest<YourManagedClass>(entityName: "YourManagedClass")
        fetchRequest.predicate = NSPredicate(format: "uuid = %@", argumentArray: [uuid])

        let object: YourManagedClass
        do {
            let objects = try context.fetch(fetchRequest)
            guard let foundObject = objects.first else {
                return
            }

            object = foundObject
        } catch {
            // Handle Error
            return
        }

        object.recid = NSNumber(value: recID)

        do {
            try context.save()
        } catch {
            // Handle Error
        }
    }
}

然后，您将调用此函数并引用您的NSManagedObjectContext（此处为“context”）：

YourManagedClass.set(recID: 15, forObject: "909455F3-C812-4399-83B4-F96A5C32A71D", in: context)