核心数据性能：NSPredicate 比较对象
如果我的 Author NSManagedObject 模型具有 authorID 属性（由服务器确定），那么 NSFetchRequest 的性能会更好吗？ NSPredicate 按 authorID 过滤，而不是完整的 Author 对象？假设我正在获取某个 author 的所有 Book NSManagedObject。哪种 predicateFormat 更好？
[NSPredicate predicateWithFormat:@"author = %@", anAuthor]
或
[NSPredicate predicateWithFormat:@"author.authorID = %@", anAuthor.authorID]
分析此问题的最佳方法是什么？我使用 OCUnit (SenTestingKit) 进行核心数据测试。 iOS 是否有类似 Ruby 的 Benchmark 模块？
If my Author NSManagedObject model has a authorID attribute (determined by the server), will an NSFetchRequest perform better if the NSPredicate filters by authorID rather than the complete Author object? Let's say I'm fetching all Book NSManagedObjects by a certain author. Which predicateFormat is better?
[NSPredicate predicateWithFormat:@"author = %@", anAuthor]
or
[NSPredicate predicateWithFormat:@"author.authorID = %@", anAuthor.authorID]
What's the best way to profile this? I have Core Data testing working with OCUnit (SenTestingKit). Does iOS have something like Ruby's Benchmark module?
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可能值得使用
-com.apple.CoreData.SQLDebug 1 参数运行您的应用程序，详细信息 此处。然后，您可以查看 Core Data 是否在两种情况下执行相同的 SQL（假设您使用的是 SQLite 存储）。
It might be worth running your app with an argument of
-com.apple.CoreData.SQLDebug 1, as detailed here.You could then see if Core Data was executing the same SQL in both circumstances (assuming you're using a SQLite store).
第一个（仅使用
Author）可能会更快，但只有测试才能确定。如果您获取（例如
Book）与Author有关系的对象并且使用谓词，SQLite 可以查看合并表是否从
Book到Author具有该给定author的正确主键。换句话说，谓词变成对Author实体主键的检查。不过，CoreData 仍然需要查阅合并表。如果您使用
，则 SQLite 必须将合并表与实际的 AuthorID 表进行连接，然后匹配生成的authorID 列。那将是更多的工作。如果
authorID没有被索引，它就会崩溃。The first one (using just
Author) would probably be faster, but only testing will tell you for sure.If you fetch (e.g.
Book) objects that have an relationship toAuthorand you use a predicateSQLite can see if the merge table from
BooktoAuthorhas the right primary key for that givenauthor. In other words, the predicate turns into a check for theAuthorentities primary key. CoreData still has to consult the merge table, though.If you use
then SQLite will have to
jointhe merge table with the actualAuthortable and then match the resultingauthorIDcolumn. That would be more work. And it would break down ifauthorIDisn't indexed.