ios - 以编程方式更新 coredata 中的重复值？

Question

我是核心数据的新手。我想更新重复值。例如我的桌子看起来像这样

 id | Name
============
 1  | Joseph  
 2  | Fernandez  
 3  | Joseph
 4  | James

假设我想将 id 1 和 4 对应的 Joseph 更新为“myName”。当我尝试更新它时，它只更新第 4 行。我在任何文档中都找不到任何方法来做到这一点。谁能建议我一个解决方案？

还有一个问题，如何打印所有名称值？

Answer 1

您必须阅读文档以了解如何更新记录 http://www.appcoda.com/core-data-tutorial-update-delete/

Answer 2

詹姆士，

我将尝试使用示例代码回答您的两个问题。

要更新特定对象，您需要NSFetchRequest使用谓词设置新对象，获取对象（类型为NSManagedObject），更新您感兴趣的值并保存上下文。

因此，例如：

NSFetchRequest* fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"YourEntityName"];
// set the predicate (it's equal to set a WHERE SQL clause) filtering on the name for example
// use camel case notation if possible, so instead of Name use name (for this you have to changes your model, if you don't want to do it use Name)
[fetchRequest setPredicate:[NSPredicate predicateWithFormat:@"name == %@", @"Joseph"]];

NSError* error = nil;
NSArray* results = [context executeFetchRequest:fetchRequest error:&error];
// do some error checking here...
for (NSManagedObject resultItem in results) {

    // use KVC (for example) to access your object properties
    [resultItem setValue:@"myName" forKey:@"name"];
}

// save your context here
// if you don't save, changes are not stored

要打印，您需要创建一个新的NSFetchRequest，抓取对象（类型NSManagedObject）并使用NSLog.

例如：

NSFetchRequest* fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"YourEntityName"];

NSError* error = nil;
NSArray* results = [context executeFetchRequest:fetchRequest error:&error];
// do some error checking here...
for (NSManagedObject resultItem in results) {

    NSLog(@"%@", [resultItem valueForKey:@"name"]);
}

PS 我提供的代码非常简单，我用于特定值的谓词检查name. 由于这可能容易出错，我会修改模型并为您需要使用的每个对象使用一种guid（我不知道 id 是否适用，但我会将其名称更改为另一个名称，例如userId）。完成后，您可以对其进行检查。

希望有帮助。

Answer 3

It's as simple as retrieving the NSManagedObject and changing the Name property. You can retrieve the NSManagedObject with a fetch request. Once you changed the property and you want to keep it changed even when you close the application you'll have to do a save on the managedObjectContext.

You'll have to read over the documentation to get up to speed on core data: http://developer.apple.com/library/mac/#documentation/cocoa/Conceptual/CoreData/Articles/cdBasics.html#//apple_ref/doc/uid/TP40001650-TP1

Edit: just NSLog whatever you want to know, for example log you fetch request results.