核心数据获取一对多实体

Question

问题：

由于未捕获的异常“NSInvalidArgumentException”导致应用程序终止错误，原因：“此处不允许使用多对多键”。

我想获取 Section 和 News 实体中的所有属性。但是这些属性应该相互匹配。例如，假设我有一个栏目名称 =“yy”，其匹配的新闻是 title="sports" 和 title="daily news"。另一个部分名称 =“aa”，只有一个匹配的新闻标题，即 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）。

1. 这是核心数据结构：

1. 我有新闻和部分的实体类：（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
   

2. 我使用 NSDictionary 将值插入到这些实体中：

   -(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;
    }
   

3. 这是我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
       }
   }
   

4. 这是我获取所有实体属性的方式：

   -(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

其实我们可以通过 ValueForKey 轻松获取一对多的属性。

// 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.... :)