复杂对象上的自定义NSSortDescriptor [英] Custom NSSortDescriptor on complex object

问题描述

这是我的第一篇文章这么抱歉，如果我不尊重所有的约定，尽管我会尽我所能。我总是找到解决我的问题在SO之前，但我完全停留在一个相当复杂的Cocoa问题。

It's my first post so sorry if I may not respect all the conventions even though I'll try my best. I have always found solutions to my problems on SO before but I'm completely stuck on a rather complex Cocoa problem.

我试图实现一个复杂的排序列表的CoreData对象。我有一个目录组成的书对象，它可以是佐贺的一部分（第一本书及其续集）。简单的结构看起来像这样：

I am trying to achieve a complex sort on a list of CoreData objects. I have a catalog composed of Book objects, which can be part of Saga (first book and its sequels). The simplified structures look like this:

@interface Book : NSManagedObject
@property (nonatomic, retain) NSString * title;
@property (nonatomic, retain) NSNumber * tomaison; //volume numbering
@property (nonatomic, retain) Saga *fromSaga;

@interface Saga : NSManagedObject
@property (nonatomic, retain) NSString * title;

我试图对我的CoreData数据库执行查询：

I'm trying to perform a query on my CoreData db, on Book:

NSEntityDescription *entity = [NSEntityDescription entityForName:@"Book" inManagedObjectContext:context];

我需要三个步骤：

1）按照书籍的类型排序（不包括在上面的代码中，因为不需要它）：

1) Sort by book's Genre (not included in the code above because it's not needed), which is performed with:

NSSortDescriptor* mainSort = [[NSSortDescriptor alloc] initWithKey:@"ofGenre.title" ascending:YES selector:@selector(localizedCaseInsensitiveCompare:)];

2）按Saga标题排序，如果这本书是佐贺的一部分

2) Sort by Saga title if the book is part of a Saga

NSSortDescriptor* secondarySort = [[SagaTitleSortDescriptor alloc] initWithKey:@"fromSaga" ascending:YES];

自定义排序描述符由以下内容定义：

Where the custom sort descriptor is defined by:

#define NULL_OBJECT(a) ((a) == nil || [(a) isEqual:[NSNull null]])
@interface SagaTitleSortDescriptor : NSSortDescriptor {}
@end
@implementation SagaTitleSortDescriptor
- (id)copyWithZone:(NSZone*)zone
{
    return [[[self class] alloc] initWithKey:[self key] ascending:[self ascending] selector:[self selector]];
}
- (NSComparisonResult)compareObject:(id)object1 toObject:(id)object2
{
    if (NULL_OBJECT([object1 valueForKeyPath:[self key]])) {
        if (NULL_OBJECT([object2 valueForKeyPath:[self key]])) 
            return NSOrderedSame;
        return NSOrderedDescending;        
    }
    if (NULL_OBJECT([object2 valueForKeyPath:[self key]])) {
        return NSOrderedAscending;
    }
    return [super compareObject:[(Saga*)object1 title] toObject:[(Saga*)object2 title]];
}
@end

3）按卷编号排序的佐贺，否则，按书名排序。这是我的问题，因为我不知道什么键发送和什么放在我的描述符（我甚至不确定是可能的）。

3) Sort by Volume Numbering IF it is part of a Saga, otherwise, sort by Book Title. Here is my problem, as I don't know what key to send and what to put in my descriptor (I'm not even sure it's possible).

NSSortDescriptor* thirdSort = [[SagaTomaisonOrBookTitleSortDescriptor alloc] initWithKey:@"self" ascending:YES];  

到目前为止，我发现@self允许发送被查询的对象似乎不允许查询发送对象内的参数。作为参考，我尝试了一些代码：

So far, I've found that @"self" allows to send the object being queried but it doesn't seem to allow queries of parameters inside the sent object. For reference, there is some code I tried:

- (NSComparisonResult)compareObject:(id)object1 toObject:(id)object2
{
    if (NULL_OBJECT([(Book*)object1 fromSaga]) && NULL_OBJECT([(Book*)object2 fromSaga])) {
        return [super compareObject:[(Book*)object1 title] toObject:[(Book*)object2 title]];
    }
    if (NULL_OBJECT([(Book*)object1 fromSaga])) {
        return NSOrderedDescending;
    }
    if (NULL_OBJECT([(Book*)object2 fromSaga])) {
        return NSOrderedAscending;
    }
    return [super compareObject:[(Book*)object1 tomaison] toObject:[(Book*)object1 tomaison]];
}

有什么想法，我能做些什么？

Any idea what I can and should do ?

谢谢！

编辑：最后一行中有一个类型

there was a type in the last line

推荐答案

如果你不使用基于SQL的存储，你可以通过传递self作为你的key和比较：作为选择器，然后实现那个自定义选择器。也就是说，在你的书类上创建一个名为compare的方法，并且只使用它的所有逻辑，而不是使用多个排序描述符。

If you're not using an SQL-based store, you could do this by passing self as your key and compare: as the selector, then implement that custom selector. That is, make a method on your book class called compare: and just have it do all of your logic rather than using multiple sort descriptors.

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