Question

问题：

由于未捕获的异常'NSInvalidArgumentException'而终止应用程序时出错，原因是：'to-many key not here here'。

我想获取Section和News实体中的所有属性。但这些属性应该相互匹配。例如，假设我有一个部分名称=“yy”，其匹配的新闻是title =“sports”和title =“每日新闻”。另一个部分名称=“aa”，只有一个匹配的新闻标题是title =“Horoscopes”等等...获取正确的部分属性及其正确的新闻属性（一个或多个）。

以下是核心数据结构：

enter image description here

我有实体类的新闻和部分:(自动生成）

//News.h:
@class Section;
@interface News : NSManagedObject

@property (nonatomic, retain) NSNumber * id;
@property (nonatomic, retain) NSString * updated;
@property (nonatomic, retain) NSString * title;
@property (nonatomic, retain) NSString * synopsis;
@property (nonatomic, retain) NSString * pub_date;
@property (nonatomic, retain) NSNumber * imageId;
@property (nonatomic, retain) Section *sectionRelation;
@end

// News.m define those attribute as @dynamic

// Section.h 
@class News;
@interface Section : NSManagedObject

@property (nonatomic, retain) NSString * name;
@property (nonatomic, retain) NSSet *newsRelation;
@end

@interface Section (CoreDataGeneratedAccessors)
- (void)addNewsRelationObject:(News *)value;
- (void)removeNewsRelationObject:(News *)value;
- (void)addNewsRelation:(NSSet *)values;
- (void)removeNewsRelation:(NSSet *)values;

// section.m still @dynamic

我使用NSDictionary将值插入这些实体：

-(Section*)insertSectionEntity:(NSDictionary*)values
{
   Section* sectionObject = [NSEntityDescription     insertNewObjectForEntityForName:ENTITY_NEWS_SECTION inManagedObjectContext:[[CoreDataHelper  coreDataManager]managedObjectContext]];
   [sectionObject setValuesForKeysWithDictionary:values];
   // I did not use [section addNewsRelationObject:news]; I used in somewhere else.
   return sectionObject;
 }

 -(News*)insertNewsEntity:(NSDictionary*)values
{
   News* newsObject = [NSEntityDescription insertNewObjectForEntityForName:ENTITY_NEWS inManagedObjectContext:[[CoreDataHelper coreDataManager]managedObjectContext]];
   [newsObject setValuesForKeysWithDictionary:values];
   return newsObject;
 }

以下是将两个实体存储到核心数据中的方式：

// this array include the NSDictionary values of Section and News entity
-(void)storeNewsAndSectionEntity:(NSMutableArray*)array
{
   if(array.count!=0){
      News* news       = NULL;
      Section* section = NULL;

     // break into two different dictionaries and store in core data
     for (NSDictionary* dic in array) {
        // name is the attribute of section
        if([dic valueForKey:@"name"]!=nil){
            section = [self insertSectionEntity:dic];
         }
         else{
            news = [self insertNewsEntity:dic];
            [section addNewsRelationObject:news]; // generate relation
         }
      }
      [[CoreDataHelper coreDataManager]saveContext]; // save context
    }
}

以下是我获取所有实体属性的方法：

-(NSArray*)fetchCoreDataNews:(Section*)section
{
    if([[CoreDataHelper coreDataManager]isEntityExist:@"News"]){

     // fectch news in relation with that specific section
     NSArray* newsArray = [[CoreDataHelper coreDataManager]fectchEntityBaseOnPredicate:@"News" withPredicate:@"SUBQUERY(sectionRelation, $x, $x.newsRelation == %@).@count != 0" withObject:section];        
     return newsArray;
    }
    else
     return nil;
 }

-(NSArray*)fetchCoreDataSection
{
   if([[CoreDataHelper coreDataManager]isEntityExist:@"Section"]){
       NSArray* sectionArray = [[CoreDataHelper coreDataManager]fectchAllAttributesFromEntity:@"Section"];
       return sectionArray;
   }
   else
     return nil;
}

 // I think this causing the problem:  Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'to-many key not allowed here'
 -(NSArray*)fectchEntityBaseOnPredicate:(NSString*)entityName withPredicate: (NSString*)predicateString withObject:(id)ManagedObject
 {

   NSManagedObjectContext *managedObjectContent = [[CoreDataHelper coreDataManager] managedObjectContext];
   NSFetchRequest *fetchRequest = [[NSFetchRequest alloc]init];
   NSEntityDescription *entity = [NSEntityDescription entityForName:entityName inManagedObjectContext:managedObjectContent];

   NSPredicate *predicate = [NSPredicate predicateWithFormat:predicateString, ManagedObject];
   [fetchRequest setPredicate:predicate];
   [fetchRequest setEntity:entity];
   NSArray* fectechedElements = [managedObjectContent executeFetchRequest:fetchRequest error:nil]; // SELECT
   return fectechedElements;
  }

谢谢！

Answer 1

实际上，我们可以通过使用ValueForKey轻松获得一对多的属性。

// get section entity
_sectionArray = [[[CoreDataControl initCoreDataControl]fetchCoreDataSection]mutableCopy];

// call relation name of each section
NSSet *news = [[_sectionArray objectAtIndex:0] valueForKey:@"newsRelation"];    

// get all related news entities in the parents entity
NSArray* allObjects = [news allObjects];

// then you can call each specific attribute in that entity
[[allObjects objectAtIndex:0]valueForKey:@"title"]; // it will return the attribute.... :)

核心数据获取一对多实体

1 个答案: