ios - Core Data sync with JSON API -

my data model named "person" , has 3 attributes "id", "firstname", , "lastname"

when importing json data using afnetworking want able check whether entity exists or not within core data using "id" identifier. if isn't there create it, , if there merge item or update it.

right have method called duplicatecheck looks like:

nspredicate *predicate = [nspredicate predicatewithformat:@"id==%@", _person.id]; nsfetchrequest *fetch = [[nsfetchrequest alloc] init]; nserror *error = nil; [fetch setentity:[nsentitydescription entityforname:@"person" inmanagedobjectcontext:self.managedobjectcontext]]; [fetch setpredicate:predicate]; nsarray *items = [self.managedobjectcontext executefetchrequest:fetch error:&error]; (nsmanagedobject *object in items) { // not sure how check here , insert or update  // save , call during api request? } 

i have predicate set not sure go here. looping on each item right way go or going wrong way?

usually 1 expect identifier unique. therefor if predicate return 0 objects, know object new. if 1 returned know object exists , maybe need update it.

nsarray *items = [self.managedobjectcontext executefetchrequest:fetch error:&error]; if(items){      if([items count] == 0){         //the object not present yet. create it.     } else if([items count] == 1) {         nsmanageobject *obj = items[0];         //there 1 object. change properties if needed      } else {         //what if several objects have same identifier???     } } else {     //handle error error object }