swift2的NSPredicate最大时间

Question

I am using coredata and I want to find maximum time in coredata. How do I write?

  let predicate = NSPredicate(format: "contentDate = '？？？' ", "")
    fetchRequest.predicate = predicate

Answer 1

To find a maximum it makes more sense to sort and ask for the first item than to try to create a predicate.

You can also look at an expression using @max to get the value back on its own if the container object isn't important.

Answer 2

As Wain said, to find maximum value you rather have to define SortDescriptor then Predicate :

let sortByTimeDescriptor = NSSortDescriptor(key: "time", ascending: false)
fetchRequest.sortDescriptors = [sortByTimeDescriptor]

You are interested just in the one (maximum) value so it's also good practice to set fetch limit for performance reason:

fetchRequest.fetchLimit = 1

Then just execute request and get first object from results array:

let results = managedObjectContext.executeFetchRequest(fetchRequest)
let maxTimeEntity = results.first

Notice that executeFetchRequest can throw and error and you have to handle it somehow.