iPhone核心数据：如何将NSSet从一个实体复制到另一个实体？

Question

This code is used to make "initial data" or "test data".

The Category entity will carry default types . The Subcategory entity will copy default types from the Category . They wouldn't be using the same types because new or old types may be deleted or added to the Subcategory .

    -(void)newCat:(NSString*)catName subCat:(NSArray*)subCatNames types:(NSArray*)typeNames{
 //get the context
 NSManagedObjectContext *context = [self managedObjectContext];

 //make a category
 Category *theCat = [NSEntityDescription
      insertNewObjectForEntityForName:@"Category" 
      inManagedObjectContext:context];
 theCat.name = catName;

 //make default types and put it in the category
 for (int i = 0; i < [typeNames count]; i++) {
  Type *type = [NSEntityDescription
       insertNewObjectForEntityForName:@"Type" 
       inManagedObjectContext:context];
  type.name = [typeNames objectAtIndex:i];
  [theCat addTypesObject:type];
 }

 //make some subcategories
 //copy default types from category to subcategory
 for (int i = 0; i < [subCatNames count]; i++) {
  Subcategory *newSubcat = [NSEntityDescription
       insertNewObjectForEntityForName:@"Subcategory" 
       inManagedObjectContext:context];

  newSubcat.name = [logbookNames objectAtIndex:i];
  newSubcat.category = theCat;
  [newSubcat addTypes:theCat.types];
 }

 //save the context
 [self save];

 }

This method works the first time I open the app. Once I terminate and reopen the app, all but one Subcategory entity retains the types .

Why is the other Subcategory removing their types ? I fear that I'm only setting a pointer to the default types in the Category .

How do I make a copy Category.types and set it as the types in Subcategory.types ?

Design wise, should I create a new entity to hold default types for the Category instead of using the same entity for defaults and non-defaults?

Answer 1

您键入的内容是一个标准对象，您可以接收并进行[types copy]（类型复制），然后您可以使用它进行所需的操作。