核心数据：按关系属性排序
我正在 GitHub 上构建一个 iPhone 原生消息应用程序的开源克隆，名为 AcaniChat。
我有一个 Conversation 实体和一个带有 sentDate 属性的 Message 实体。每个Conversation可以有许多Message。如何获取按最早的消息的sentDate排序的对话？
I'm building an open-source clone of iPhone's native Messages app called AcaniChat on GitHub.
I have a Conversation entity and a Message entity with a sentDate attribute. Each Conversation can have many Messages. How do I fetch Conversations sorted by the sentDate of it's oldest Message?
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我能想到的最好方法是向名为
lastMessageSentDate的Conversation实体添加一个属性，并且每次Message传入时添加到对话，将该对话的lastMessageSentDate设置为该消息的sentDate。我可能还想向Conversation实体添加一个名为lastMessageText的属性，因为我想在上显示对话的最后一条消息的文本>ConversationsViewController（就像原生 iPhone 消息应用程序一样），这样做将使我不必为Message执行另一次核心数据获取。其实我只是有一个想法！也许我可以按
[email protected] 对，根据Xcode 文档：键值编码编程指南：集合运算符。对话进行排序]The best way I can think of doing this is by adding an attribute to the
Conversationentity calledlastMessageSentDateand, every time aMessagecomes in and gets added to aConversation, setting that conversation'slastMessageSentDateto that message'ssentDate. I'll also probably want to add an attribute calledlastMessageTextto theConversationentity as well because I want to show the text of the last message for a conversation on theConversationsViewController(just like the native iPhone Messages app does), and doing so will save me from having to do another Core Data fetch for theMessage.Actually, I just had an idea! Maybe I can sort
Conversations by[email protected], according to Xcode Documentation: Key-Value Coding Programming Guide: Collection Operators.