Question

需要按类别产品的数量/数量对按提取请求检索的类别列表进行排序。然后，我希望能够手动将几个类别（已过滤掉）添加到数组中，以便它们位于列表的底部。我一直遇到包含KVC聚合的＆＃34; Keypath的错误，其中不应该是一个......＆＃34;当我尝试按产品数排序时。

我在这里错过了什么/做错了什么？谢谢！

Category.h

@class Category;

@interface Category : NSManagedObject

@property (nonatomic, strong) NSString *name;
@property (nonatomic, strong) NSSet *products;

@end

Product.h

@class Category;

@interface Product : NSManagedObject

@property (nonatomic, strong) NSString *sku;
@property (nonatomic, strong) NSString *name; // Product name
@property (nonatomic, strong) NSString *prodDescription;
@property (nonatomic, strong) Category *category; // Product category
@property (nonatomic, strong) NSString *upc;
@property (nonatomic, strong) NSString *countryCode;
@property (nonatomic, strong) NSString *webpage;
@property (nonatomic, strong) NSString *manual;
@property (nonatomic, strong) NSString *quickStart;
@property (nonatomic, strong) UIImage *thumb;
@property (nonatomic, strong) NSString *thumbURLString;
@property (nonatomic, strong) UIImage *mainImg;
@property (nonatomic, strong) NSString *mainImgURLString;
@property (nonatomic, strong) UIImage *secondaryImg;
@property (nonatomic, strong) NSString *secondaryImgURLString;

@end

CategoriesViewController.m

- (NSFetchedResultsController *)fetchedResultsController {

    if (_fetchedResultsController == nil) {
        NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
        [fetchRequest setEntity:[NSEntityDescription entityForName:@"Category" inManagedObjectContext:self.managedObjectContext]]; // Fetch categories
        NSArray *sortDescriptors = nil;
        NSString *sectionNameKeyPath = nil;
        // Sort by number of products in category
        sortDescriptors = [NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:@"category.@count" ascending:NO]];
        [fetchRequest setSortDescriptors:sortDescriptors];

        // Use predicate to exclude Accessories and Replacement Parts categories from initial array
        NSPredicate *predicate = [NSPredicate predicateWithFormat:@"name != 'Accessories' AND name != 'Replacement Parts'"];
        [fetchRequest setPredicate:predicate];

        _fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
                                                                    managedObjectContext:self.managedObjectContext
                                                                      sectionNameKeyPath:sectionNameKeyPath
                                                                               cacheName:nil];

        }
    return _fetchedResultsController;
}

Answer 1

你应该使用像这样的多对多关系

Answer 2

通常，这可以通过在记录本身中设置计数变量来解决。这允许获取的结果控制器对该计数的值进行排序。我在相关关系的自定义设置器中保留了这种计数。在您的情况下，这可能是products的集合，新变量可能被称为productCount。 Xcode有一个片段模板用于此类事情。这是一个例子：

- (void) addProductsObject: (Product *) value {

    NSSet *changedObjects = [NSSet setWithObject:value];

    [self willChangeValueForKey: kDays withSetMutation: NSKeyValueUnionSetMutation usingObjects: changedObjects];
    [[self primitiveValueForKey: kDays] addObject: value];
    [self  didChangeValueForKey: kDays withSetMutation: NSKeyValueUnionSetMutation usingObjects: changedObjects];

    self.productCount = (int32_t)self.products.count;

} // -addProductsObject:

其他三种方法同样简单明了。

根据多对多关系

2 个答案: