问题
I'm trying to create a sort descriptor, for a core data fetch request, that will fetch objects that are ordered by a calculated value (e.g., the sum of two or more attributes). Is this possible? Thanks in advance.
回答1:
From the "Core Data Programming Guide":
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.
So sorting by a calculated value seems not to be possible. You have to pre-calculate the sorting value and store it as (non-transient) attribute in your objects.
来源：https://stackoverflow.com/questions/11927762/how-to-sort-based-on-a-calculated-value-from-multiple-core-data-attributes