xcode 核心数据，一对多子对象排序
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Core data, sorting one-to-many child objects
提问by Shizam
So, lets say I have a store of parents children and the parent has a one to many relationship to children (parent.children) and they all have first names. Now, on the initial fetch for parents I can specify a sort descriptor to get them back in order of first name but how can I request the children in order? If I do a [parent.children allObjects] it just gives them back in a jumble and I'd have to sort after the fact, every time.
所以，假设我有一个父母孩子的商店，父母与孩子有一对多的关系（parent.children），他们都有名字。现在，在对父母的初始提取时，我可以指定一个排序描述符以按名字的顺序将它们取回，但是我如何按顺序请求孩子？如果我做一个 [parent.children allObjects] 它只会把它们弄得一团糟，我每次都必须事后排序。
Thanks, Sam
谢谢，山姆
回答by shosti
If you just want to use an NSArray, and not an NSFetchedResultsController, there's another way:
如果您只想使用 NSArray 而不是 NSFetchedResultsController，还有另一种方法：
NSSortDescriptor *alphaSort = [NSSortDescriptor sortDescriptorWithKey:@"firstName" ascending:YES];
NSArray *children = [[parent.children allObjects] sortedArrayUsingDescriptors:[NSArray arrayWithObject:alphaSort]];
回答by Tim Isganitis
Sam,
山姆，
If I read your question correctly, you want to set up a fetch that returns a sorted list of the children of a specific parent. To do this, I would set up a fetch for "children" entities and then use a predicate to limit the results:
如果我正确阅读了您的问题，您希望设置一个 fetch 返回特定父级的子项的排序列表。为此，我将为“子”实体设置提取，然后使用谓词来限制结果：
NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease];
[request setEntity:[NSEntityDescription entityForName:@"children" inManagedObjectContext:moc]];
[request setSortDescriptors:[NSArray initWithObject:[[NSSortDescriptor alloc] initWithKey:@"firstName" ascending:YES]];
[request setPredicate:[NSPredicate predicateWithFormat:@"(parent == %@)", parent]];
Obviously, your entity and attribute names may be different. In the last line, the parent variable should be a reference to the NSManagedObject instance of the parent whose children you want.
显然，您的实体和属性名称可能不同。在最后一行中，父变量应该是对您想要其子对象的父对象的 NSManagedObject 实例的引用。
