Question

此应用程序将ARC和Core Data与SQLite数据库一起使用。在OSX 10.8上使用Xcode 4.6开发。该数据库包含许多实体，其中几个实体处于父/子关系中。一切都很好，除了涉及父/子关系中两个实体的情况，它们与其他实体不同，因为它们包含数值属性，这些属性是对这两个实体的其他属性执行的数学运算的结果。

子实体包含属性A，B和C（其中C = A * B）。父实体包含属性X（其中X =其子C的总和）。

数据在同一视图中以两个NSTableView显示。我使用绑定来填充表。当我单击一个单元格来修改B时，C应该立即在同一个表中更新，而X在另一个表中更新。当我添加或删除孩子时，X也应该立即更新。

有两个问题。

当我修改B时，C立即更新，但X不是。当我添加或删除子项时，X也不会更新。为了更新X，我需要保留记录并在表格中选择另一个（然后我可以看到先前选择的记录的X得到更新）。
退出应用程序时，C和X的修改值不会写入数据库文件中。

我的代码中遗漏了什么？这是我的托管对象类。我修改了属性和类名以使其更清晰。

// header of parent

#import <Foundation/Foundation.h>
#import <CoreData/CoreData.h>
@class Child;
@interface Parent : NSManagedObject
@property (nonatomic, retain) NSDecimalNumber * parent_X;
@property (nonatomic, retain) NSSet *children;
@end

@interface Parent (CoreDataGeneratedAccessors)
- (void)addChildrenObject:(NSManagedObject *)value;
- (void)removeChildrenObject:(NSManagedObject *)value;
- (void)addChildren:(NSSet *)values;
- (void)removeChildren:(NSSet *)values;
@end


// implementation of parent

#import "Parent.h"
@implementation Parent
@dynamic parent_X;
@dynamic children;
- (void)addChildrenObject:(NSManagedObject *)value {
    NSSet *s = [NSSet setWithObject:value];
    [self willChangeValueForKey:@"children" withSetMutation:NSKeyValueUnionSetMutation usingObjects:s];
    [[self primitiveValueForKey:@"children"] addObject:value];
    [self didChangeValueForKey:@"children" withSetMutation:NSKeyValueUnionSetMutation usingObjects:s];
}
- (void)removeChildrenObject:(NSManagedObject *)value {
    NSSet *s = [NSSet setWithObject:value];
    [self willChangeValueForKey:@"children" withSetMutation:NSKeyValueMinusSetMutation usingObjects:s];
    [[self primitiveValueForKey:@"children"] removeObject:value];
    [self didChangeValueForKey:@"children" withSetMutation:NSKeyValueMinusSetMutation usingObjects:s];
}
- (void)addChildren:(NSSet *)values {
    NSSet *s = [NSSet setWithObject:values];
    [self willChangeValueForKey:@"children" withSetMutation:NSKeyValueUnionSetMutation usingObjects:s];
    [[self primitiveValueForKey:@"children"] addObject:values];
    [self didChangeValueForKey:@"children" withSetMutation:NSKeyValueUnionSetMutation usingObjects:s];
}
- (void)removeChildren:(NSSet *)values {
    NSSet *s = [NSSet setWithObject:values];
    [self willChangeValueForKey:@"children" withSetMutation:NSKeyValueMinusSetMutation usingObjects:s];
    [[self primitiveValueForKey:@"children"] removeObject:values];
    [self didChangeValueForKey:@"children" withSetMutation:NSKeyValueMinusSetMutation usingObjects:s];
}
- (NSDecimalNumber *)parent_X {
    return [self valueForKeyPath:@"children.@sum.child_C"];
}
@end


// header of child

#import <Foundation/Foundation.h>
#import <CoreData/CoreData.h>
@class Parent;
@interface Child : NSManagedObject
@property (nonatomic, retain) NSDecimalNumber * child_A;
@property (nonatomic, retain) NSDecimalNumber * child_B;
@property (nonatomic, retain) NSDecimalNumber * child_C;
@property (nonatomic, retain) Parent *parent;
@end


// implementation of child

#import "Child.h"
#import "Parent.h"
@implementation Child
@dynamic child_A;
@dynamic child_B;
@dynamic child_C;
@dynamic parent;
- (void)awakeFromInsert {
    [super awakeFromInsert];
    [self setValue:@50.00f forKey:@"child_A"];
    [self setValue:@1.00f forKey:@"child_B"];
} 
-(NSDecimalNumber *)child_C {
    return [[self child_A] decimalNumberByMultiplyingBy:[self child_B]];
}
@end

Answer 1

在您的代码中，您似乎在添加或删除对象后未保存到CoreData。我不确定Xcode 4.6，但在4.6.3中，Xcode自动填充以下方法：

- (void)saveContext
{
    NSError *error = nil;
    NSManagedObjectContext *managedObjectContext = self.managedObjectContext;
    if (managedObjectContext != nil) {
        if ([managedObjectContext hasChanges] && ![managedObjectContext save:&error]) {
            // Replace this implementation with code to handle the error appropriately.
            // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
            NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
            abort();
        }
    }
}

你有没有它，你只是忘了打电话给它？如果您没有填充，则需要添加它以将更改保存到CoreData。

或者，您只需从- (BOOL)save:(NSError **)error致电NSManagedObjectContext。

核心数据对象修改的属性不会立即在tableview中更新，也不会保存

1 个答案: