Question

假设每个企业都有许多目录，每个目录都有很多业务。

说我有一个Business对象。该Business对象有10个catalogID。

目前我会使用代理对象。 MutableSetForKey然后删除“差异”。这非常麻烦。

-(void)saveManytoManyRelationship:(NSString *) relationshipInDict andRelationshipInCoreData:(NSString*) relationshipInCoreData withTable: (NSString*) table andAttribute: (NSString*) attribute andDict: (NSDictionary *) dict andDictToSave: (NSDictionary *) dictToSave forBiz: (Business* ) BusinessToSave
{
    if([dict[relationshipInDict] isNotEmpty] && [dict[relationshipInDict][0] class]!=[NSNull class]){
        NSMutableArray * DownloadedRelationship =dict[relationshipInDict];
        NSMutableSet * ObjectsReturned=[NSMutableSet set];
        for(int i=0;i<[DownloadedRelationship count];i++){
            //NSDictionary * dictOfTag=;
            NSString * Value=DownloadedRelationship[i];
            NSManagedObject * thisTag= [self lookUpFromDictToSave:table withAttribute:attribute withValue:Value withDataCache:dictToSave];
            [ObjectsReturned addObject:thisTag];
        }
        NSMutableSet * manyManagedObjects = [BusinessToSave mutableSetValueForKey:relationshipInCoreData];
        //PO1(TagsReturn);
        [self removeDifferenceBetween2MutableManagedObjectSets:manyManagedObjects withDownloadedVersion:ObjectsReturned];
    }
}

-(void) removeDifferenceBetween2MutableManagedObjectSets:(NSMutableSet *) original withDownloadedVersion:(NSMutableSet *) downloaded {
    for (NSManagedObject * someObject in downloaded)
    {
        if ([downloaded containsObject:someObject] && ! [original containsObject:someObject])
        {
            [original addObject:someObject];
        }
        else if (![downloaded containsObject:someObject] && [original containsObject:someObject])
        {
            [original removeObject:someObject];
        }
        else
        {
        }
    }
}

有更简单的方法吗？

Answer 1

通过使用Core Data自动生成的方法（当您使用Xcode创建NSManagedObject子类时）非常容易。

for (Catalog *catalog in catalogsToBeAdded) {
  [business addCatalogObject:catalog];
}

甚至更简单：

[business addCatalogObjects:catalogsToBeAdded];

无需插入反向关系。这会自动发生。

此外，您不必担心重复数据删除。多对多关系的类型为NSSet，因此根据定义，没有重复项。如果你添加两次相同的对象，第二次将没有任何效果。

如何在Core Data中分配多对多的关系？

1 个答案: