Question

我只使用-setPropertiesToFetch获取实体的一些属性和一对一关系，并将结果类型设置为NSDictionaryResultType。现在我在访问返回的关系的属性时遇到问题。只要我想访问一个属性，我就会得到一个NSInvalidArgumentException'，原因是：无法识别的选择器被发送到实例

以下是完整的例外：

2011-03-23 11:02:10.435 ThurboApp[32996:207] -[_NSObjectID_48_0 lon]: unrecognized selector sent to instance 0x5a3f490
2011-03-23 11:02:10.441 ThurboApp[32996:207] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[_NSObjectID_48_0 lon]: unrecognized selector sent to instance 0x5a3f490'

以下是相应的源代码：

    - (void)fetchAllPois
{
    NSFetchRequest *request = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"POI" inManagedObjectContext:self.managedObjectContext];
    request.entity = entity;
    [request setResultType:NSDictionaryResultType];
    [request setPropertiesToFetch:[NSArray arrayWithObjects:@"poiId",@"categoryId",@"poiTitle",@"coordinates", nil]];
    request.sortDescriptors = nil;
    request.predicate = nil;

    NSError *error = nil;
    self.fetchResult = [self.managedObjectContext executeFetchRequest:request error:&error];

}


- (MapPoint *)createMapPointFromDictionary:(NSDictionary *)dict
{
    NSString *poiId = [dict objectForKey:@"poiId"];
    NSString *title = [dict objectForKey:@"poiTitle"];
    Coordinates *coords = (Coordinates *)[dict objectForKey:@"coordinates"];
    NSNumber *category = [dict objectForKey:@"categoryId"];
    CLLocationCoordinate2D coordinates = CLLocationCoordinate2DMake([coords.lat doubleValue], [coords.lon doubleValue]); //here raises the exception
    MapPoint *p = [[[MapPoint alloc] initWithPoiId:poiId title:title category:[category intValue] coordinates:coordinates] autorelease];
    return p;

}

坐标界面：

@interface Coordinates :  NSManagedObject  
{
}

@property (nonatomic, retain) NSNumber * lat;
@property (nonatomic, retain) NSNumber * alt;
@property (nonatomic, retain) NSNumber * lon;
@property (nonatomic, retain) NSManagedObject * poi;

@end

我已经检查过，字典中返回的值是正确的。偶数坐标指向一个Coordinate对象。

非常感谢帮助。

Answer 1

好的，我设法解决了这个问题。你得到的关系是一个NSManagedObjectID，你可以使用objectWithID获取实体本身。这是更新的代码：

- (MapPoint *)createMapPointFromDictionary:(NSDictionary *)dict
{
    NSString *poiId = [dict objectForKey:@"poiId"];
    NSString *title = [dict objectForKey:@"poiTitle"];
    NSManagedObjectID *coordsID = (NSManagedObjectID *)[dict objectForKey:@"coordinates"]; //get the objectid
    NSNumber *category = [dict objectForKey:@"categoryId"];
    Coordinates *coords = (Coordinates *)[self.managedObjectContext objectWithID:coordsID]; //get the actual managedobject
    CLLocationCoordinate2D coordinates = CLLocationCoordinate2DMake([coords.lat doubleValue], [coords.lon doubleValue]);
    MapPoint *p = [[[MapPoint alloc] initWithPoiId:poiId title:title category:category coordinates:coordinates] autorelease];
    return p;

}

使用setPropertiesToFetch获取后访问关系属性的问题

1 个答案: