Question

-(void)passDataBack:(PersonHolder *)contact{
    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Person"];
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"firstName == %@",contact.firstName];
    [request setPredicate:predicate];
    NSError *error;
    Person *person = [[self.managedObjectContext executeFetchRequest:request error:&error]lastObject];
    [person.firstName setValue:contact.firstName forKey:@"fistName"];
    [person.lastName setValue:contact.lastName forKey:@"lastName"];

    if(![self.managedObjectContext save:&error]){

        NSLog(@"Could not save edited data");
    }

}

在运行时我可以看到contact加载了我正在传递的所有数据，但是我的人员实体没有得到更新。

我看到答案how to update core data entered values，我认为我肯定遗漏了一些东西

Answer 1

你不会错过任何东西，恰恰相反

核心数据等同于简单属性设置器

person.firstName = contact.firstName

是

[person setValue:contact.firstName forKey:@"firstName"];
[person setValue:contact.lastName forKey:@"lastName"];

还要考虑拼写错误@"fistName"

修改：尝试使用此语法

NSArray *people = [self.managedObjectContext executeFetchRequest:request error:&error];
if (error) {
    NSLog(@"%@", error);
    return;
}
if (people.count) {
    Person *person = [people lastObject];
    person.firstName = contact.firstName;
    person.lastName = contact.lastName;

    if(![self.managedObjectContext save:&error]){
       NSLog(@"Could not save edited data");
    }
} else {
    NSLog(@"result array is empty"):
}

Answer 2

而不是

[person.firstName setValue:contact.firstName forKey:@"firstName"];
[person.lastName setValue:contact.lastName forKey:@"lastName"];

使用

[person setValue:contact.firstName forKey:@"firstName"];
[person setValue:contact.lastName forKey:@"lastName"];

或

person.firstName = contact.firstName;
person.lastName = contact.lastName;

编辑：盲目地将最后一个获取查询对象分配给person对象并在核心数据中设置值之前的建议，检查你的fetch查询是否返回结果。这可能会崩溃。

NSArray *persons = [[[CoreDataManager sharedManager] context] executeFetchRequest:fetchRequest error:&error]; 

if(persons.count > 0){
 // do changes in the object
 } 
else{ 
// do what you want to do to handle this situation 
}

更新核心数据失败

2 个答案: