使用NSFetchedresultController对“transient”字段进行排序 [英] Sorting on 'transient' fields with NSFetchedresultController

问题描述

有一种方法来使用'transient'字段或类似的东西，并以某种方式相应地与NSFetchedResultsController排序。我想要执行以下操作：

Is there a way to use a 'transient' field or something like that and in some way sort accordingly with a NSFetchedResultsController. I want to do the following:

我在数据库中有位置。当一个人打开列表，我想显示最近的地方在顶部，然后根据距离排序。但是很明显，这取决于用户的位置，所以我不能使用静态字段。我希望使用一个暂时字段，你可以使用的节头。

I have location of places in a database. When a person opens the list, I want to show the nearest place on top, an then sort accordingly to distance. But clearly,this depends on the users location, so I cannot use a static field. I was hoping to use a transient field, as you can use for the section headers.

有没有人可以给这个情况的解决方案或解决方法？

Is there anybody who can give a solution or workaround for this situation?

推荐答案

您不能在SQlite基本Core Data存储的提取请求中使用瞬态属性。

You cannot use a transient property in a fetch request for a SQlite base Core Data store.

请参阅获取托管对象：

您无法使用基于瞬态的谓词properties
（虽然你可以使用瞬态属性在内存中过滤
）。 ...总而言之，如果你直接执行一个fetch，你应该
通常不添加基于Objective-C的谓词或排序描述符到
获取请求。

You cannot fetch using a predicate based on transient properties (although you can use transient properties to filter in memory yourself). ... To summarize, though, if you execute a fetch directly, you should typically not add Objective-C-based predicates or sort descriptors to the fetch request. Instead you should apply these to the results of the fetch.

您可以使用临时属性 sectionNameKeyPath ，但即使这样，您仍然需要为基于持久属性的节创建第一个排序描述符。

You can use a transient property for sectionNameKeyPath, but even then you need a first sort descriptor for the sections that is based on a persistent attribute.

可能是抓取所有对象，然后排序抓取的数组。但是，当然，你不再具有获取结果控制器的优势。

So the only workaround is probably to fetch all objects and then sort the fetched array. But then of course you don't have the advantages of a fetched results controller anymore.

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