Ios NSBatchUpdateRequest-如何根据属性的当前值计算属性的新值？_Ios_Swift_Nsfetchedresultscontroller_Nsbatchupdaterequest

Ios NSBatchUpdateRequest-如何根据属性的当前值计算属性的新值？

ios swift

Ios NSBatchUpdateRequest-如何根据属性的当前值计算属性的新值？,ios,swift,nsfetchedresultscontroller,nsbatchupdaterequest,Ios,Swift,Nsfetchedresultscontroller,Nsbatchupdaterequest,我有一个简单的NSBatchUpdateRequest： let bur = NSBatchUpdateRequest(entityName: "WLWishlist") bur.resultType = .UpdatedObjectIDsResultType bur.predicate = NSPredicate(format: "itemCount = %d", 0) bur.propertiesToUpdate = ["position": ???] //here I need to ad

我有一个简单的NSBatchUpdateRequest：

let bur = NSBatchUpdateRequest(entityName: "WLWishlist")
bur.resultType = .UpdatedObjectIDsResultType
bur.predicate = NSPredicate(format: "itemCount = %d", 0)
bur.propertiesToUpdate = ["position": ???] //here I need to add 1 to current position.

如何根据属性的当前值计算其新值