xcode - 如何使用核心数据模型编辑器（Xcode 4.3.2）指定零日期表达式？

Question

我正在尝试创建一个获取请求，而不是在代码中，而是通过使用核心数据模型编辑器来获取所有对日期属性没有值的 Book 对象。

我尝试了各种方法来指定这一点。一个例子如...

...但是，当我离开并返回数据模型编辑器时，Xcode 已将其更改为今天的日期...

如果这只是模型编辑器的限制，而在代码中进行是唯一的方法，那就这样吧。我只是想保持一致，因为我的所有其他获取请求都已在模型编辑器中完成，并且没有定义问题。

Answer 1

Aaah, this is almost a philosophical issue. nil is simply not a valid date, so it should not be in the predicate. There is a simple workaround, though:

Initialize your date to some extreme value, and check for that value (or if the date is beyond that value).

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I also noticed that perhaps in the editor it is just a display thing. If you toggle the switch in the upper right corner (Editor/Expression view I guess) you will see that the query has not changed, even if in one view today's date is displayed.

Therefore it might just work anyway. In this case it is just a display bug.