ios - 核心数据: Null Array when retrieving Data Base objects

Question

我在 NSMutableArray 中有九个 Aviso 元素，理论上我将这九个元素存储在我的应用程序的核心数据中。问题是，当尝试使用 NSFetchRequest 从数据库检索这些元素时，我只得到八个空元素，而最后一个元素正确显示。

这就是我的数据模型的样子:

Aviso 实体与 Aviso NSManagedObject 相关:

#import <Foundation/Foundation.h>
#import <CoreData/CoreData.h>

@interface Aviso : NSManagedObject{
    NSDate * date;
    NSString * text;
    NSString * idwarning;
}

@property (nonatomic, retain) NSDate * date;
@property (nonatomic, retain) NSString * text;
@property (nonatomic, retain) NSString * idwarning;

@end

在我的 WarningController 类的 viewDidLoad 中，我首先加载警告:

    for(Aviso * a in warnings)
    {
        [self saveObjectcdata:a];
    }

    [self loadxcdata];

saveObjectcdata 是:

-(void) saveObjectcdata:(Aviso * )aux
{
    NSManagedObject *object = [NSEntityDescription insertNewObjectForEntityForName:@"Aviso" inManagedObjectContext:self.managedObjectContext];

    [object setValue:aux.idwarning forKey:@"idwarning"];
    [object setValue:aux.date forKey:@"date"];
    [object setValue:aux.text forKey:@"text"];

    [managedObjectContext insertObject:object];

    // Commit the change.
    NSError *error = nil;
    if (![managedObjectContext save:&error]) {
        // Handle the error.
    }
    else{
        NSLog(@"Object saved: %@ in %@ and id: %@",aux.text,aux.date,aux.idwarning);
    }
}

并加载xcdata:

- (void) loadxcdata
{
    [xcdataarray removeAllObjects];

    if (managedObjectContext == nil) // generar el contexto del CoreData
    {
        managedObjectContext = [(EmergencyAppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext];
    }

    NSFetchRequest *request = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Aviso" inManagedObjectContext:managedObjectContext];
    [request setEntity:entity];

    // Execute the fetch -- create a mutable copy of the result.
    NSError *error = nil;
    NSMutableArray *mutableFetchResults = [[managedObjectContext executeFetchRequest:request error:&error] mutableCopy];
    if (mutableFetchResults == nil) {
        // Handle the error.
        NSLog(@"Error al recuperar:%@",error);
    }

    // Set self's events array to the mutable array, then clean up.
    [self setXcdataarray:mutableFetchResults];

    for(Aviso * war in xcdataarray)
    {
        NSLog(@"Core data object: %@ in %@ and id: %@",war.text,war.date,war.idwarning);
    }

}

这就是我在控制台中获得的内容。首先，对象被正确存储，但在再次检索它们时，我只得到最后一个:

2013-04-24 17:50:05.716 Emergencies[4286:907] CoreData: error: Failed to call designated initializer on NSManagedObject class 'Aviso' 
2013-04-24 17:50:05.844 Emergencies[4286:907] Object saved: sexto y ultimo in 2013-04-19 12:21:43 +0000 and id: 9
2013-04-24 17:50:05.905 Emergencies[4286:907] Object saved: fifth later in 2013-04-18 11:17:50 +0000 and id: 8
2013-04-24 17:50:05.961 Emergencies[4286:907] Object saved: fifth in 2013-04-18 11:17:44 +0000 and id: 7
2013-04-24 17:50:06.014 Emergencies[4286:907] Object saved: forth later in 2013-04-18 11:11:57 +0000 and id: 6
2013-04-24 17:50:06.071 Emergencies[4286:907] Object saved: cuarto in 2013-04-18 11:11:36 +0000 and id: 5
2013-04-24 17:50:06.128 Emergencies[4286:907] Object saved: tercero in 2013-04-18 10:25:01 +0000 and id: 3
2013-04-24 17:50:06.183 Emergencies[4286:907] Object saved:  in 2013-04-18 10:57:27 +0000 and id: 4
2013-04-24 17:50:06.237 Emergencies[4286:907] Object saved: rt in 2013-04-18 10:20:20 +0000 and id: 2
2013-04-24 17:50:06.296 Emergencies[4286:907] Object saved: This is the first example in 2013-04-17 08:43:45 +0000 and id: 1
2013-04-24 17:50:06.304 Emergencies[4286:907] Core data object: (null) in (null) and id: (null)
2013-04-24 17:50:06.306 Emergencies[4286:907] Core data object: (null) in (null) and id: (null)
2013-04-24 17:50:06.308 Emergencies[4286:907] Core data object: (null) in (null) and id: (null)
2013-04-24 17:50:06.310 Emergencies[4286:907] Core data object: (null) in (null) and id: (null)
2013-04-24 17:50:06.312 Emergencies[4286:907] Core data object: (null) in (null) and id: (null)
2013-04-24 17:50:06.314 Emergencies[4286:907] Core data object: (null) in (null) and id: (null)
2013-04-24 17:50:06.317 Emergencies[4286:907] Core data object: (null) in (null) and id: (null)
2013-04-24 17:50:06.319 Emergencies[4286:907] Core data object: (null) in (null) and id: (null)
2013-04-24 17:50:06.321 Emergencies[4286:907] Core data object: This is the first example in 2013-04-17 08:43:45 +0000 and id: 1

编辑:

从核心数据实体创建一个新类 Aviso 后(选择实体，然后选择编辑器 - 创建新的 NSManagedObject ，然后修改我的 中的几行>saveObjectcdata 方法现在可以工作了。

-(void) saveObjectcdata:(NSString *)warningId date:(NSDate*)date text:(NSString*)txt
{
    Aviso *object = [NSEntityDescription insertNewObjectForEntityForName:@"Aviso" inManagedObjectContext:self.managedObjectContext];

    object.idwarning = warningId;
    object.date = date;
    object.text = txt;

    // Commit the change.
    NSError *error = nil;
    if (![managedObjectContext save:&error]) {
        // Handle the error.
    }
    else{
        NSLog(@"Object saved: %@ in %@ and id: %@",object.text,object.date,object.idwarning);
    }
}

Answer 1

我明白为什么你得到空值，我不明白为什么最后一个对象保存成功。

您没有按照设计的方式使用 CoreData。

1) 您不必实现实体的内部数据结构。如果您希望用一个类来代表您的实体，请在设计中选择您的实体，然后选择:Editor->Create NSManagedObject Subclass。
除非您需要额外的功能，否则无需添加任何内容。
不要覆盖不应该覆盖的内容 see here了解更多详情。

2) 您添加新对象的方式是错误的。
要插入项目，您只需调用:[NSEntityDescription insertNewObjectForEntityForName:<EntityName> inManagedObjectContext:<context>] .
您可以将结果转换为所需的托管对象子类。

你的 saveObjectdata:应该看起来像:

-(void) saveObjectcdata:(id)warningId date:(NSDate*)date text:(NSString*)text
{
    Avisio *object = [NSEntityDescription insertNewObjectForEntityForName:@"Aviso" inManagedObjectContext:self.managedObjectContext];

    object.idwarning = warningId;
    object.date = date;
    object.text = text;

    // Commit the change.
    NSError *error = nil;
    if (![managedObjectContext save:&error]) {
        // Handle the error.
    }
    else{
        NSLog(@"Object saved: %@ in %@ and id: %@",object.text,object.date,object.idwarning);
    }
}

3) 我建议您阅读this拿到手中的东西