我用到一个核心数据模型,一对多关系模式。其中一个category,包含很多subcategories。
Category <---->> Subcategory
我想做到,判断指定的Category中是否包括具体名称的Subcategory
。
比如,现在已经有两个category,需要得知命名为Fruit的category中是否包括名为Apple的subcategory。
Vetegables
- Carrot
- Lettuce
Fruits
- Apple
- Orange
- Pear
代码如下:
- (SubCategory *)searchForSubCategoryWithName:(NSString *)subCategory
inCategory:(Category *)category
{
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"SubCategory" inManagedObjectContext:self.beer.managedObjectContext];
[fetchRequest setEntity:entity];
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"name == [c] %@", subCategory];
[fetchRequest setPredicate:predicate];
NSError *error;
NSArray *fetchedObjects = [self.beer.managedObjectContext executeFetchRequest:fetchRequest error:&error];
if (fetchedObjects != nil && fetchedObjects.count > 0) {
return [fetchedObjects objectAtIndex:0];
}
else {
return nil;
}
}