核心数据，排序一对多子对象 [英] Core data, sorting one-to-many child objects

问题描述

所以，让我说我有一个父母的孩子商店，父母与孩子（parent.children）有一对多的关系，他们都有名字。现在，在父母的初始提取，我可以指定一个排序描述符，以按姓名顺序返回，但我如何请求孩子们的顺序？如果我做一个[parent.children allObjects]，它只是给他们一个混乱，我必须排序事后，每一次。

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.

谢谢，
Sam

Thanks, Sam

推荐答案

Sam，

问题正确，您想要设置一个提取，返回一个特定父的子项的排序列表。为此，我将为children实体设置一个抓取，然后使用一个谓词来限制结果：

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:

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]];

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级的父级的NSManagedObject实例的引用。

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.

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