Realm Swift:始终将nil值排在最后 [英] Realm Swift: always put nil values last in sort

问题描述

我正在用Swift 2.2编写一个针对iOS 8并使用Realm的应用程序.我允许用户使用Results.sorted(_:ascending:)根据各种可选属性对对象进行排序.这对于降序排序非常有效，但对于升序排序，nil值放在首位，看起来不太正确.许多数据库系统都有一个NULLS FIRST/LAST选项，并且使用CoreData，它似乎可以

I'm writing an app in Swift 2.2 targeting iOS 8 and using Realm. I allow the user to sort objects based on various optional properties using Results.sorted(_:ascending:). This works very well for descending sorts but for ascending sorts, nil values are placed first which doesn't look right. Many database systems have a NULLS FIRST/LAST option and with CoreData, it looks like it's possible to subclass NSSortDescriptor. Is there any way to always put nil values last when sorting in Realm? Even if there's only a hacky strategy, that would be appreciated, too.

推荐答案

Realm不支持Results的自定义排序，而不是Results.sorted(_:ascending:)方法提供的功能.但是，您可以通过串联两个查询，甚至可以通过计算属性来公开该查询，从而轻松地自己完成此工作:

Realm doesn't support custom sorting of Results other than what the Results.sorted(_:ascending:) method gives you. But you can compose this yourself fairly easily by concatenating two queries, maybe even exposing that through a computed property:

var results: [MyModel] {
  let sorted = realm.objects(MyModel).sorted("...", ascending: true)
  return sorted.filter("optionalProperty != nil") +
         sorted.filter("optionalProperty == nil")
}

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