ios - Core Data - Insert based by parameter -

i have table called person. how make data entry based name, not repeat names.

example:

i have person named josh. can not have person named josh.

similar function of pk.

unfortunately, coredata doesn't have built-in way prevent dupes.

first, fetch request predicate see if value exists. if not exist, insert new entity.

example)

    let appdelegate = uiapplication.sharedapplication().delegate appdelegate     let managedcontext = appdelegate.managedobjectcontext!     let personname = "josh"      let fetchrequest = nsfetchrequest(entityname: "person")     let predicate = nspredicate(format: "name = %@", personname)     fetchrequest.predicate = predicate      var error: nserror?     let fetchedresults = managedcontext.executefetchrequest(fetchrequest, error: &error) [nsmanagedobject]?      if let results = fetchedresults {         // if no results found, insert         if results.count == 0 {             let entity =  nsentitydescription.entityforname("person", inmanagedobjectcontext: managedcontext)             let person = person(entity: entity!, insertintomanagedobjectcontext:managedcontext)             person.setvalue(personname, forkey: "name")              var error: nserror?             if !managedcontext.save(&error) {                 println("could not save \(error), \(error?.userinfo)")             }         }      } else {         println("could not fetch \(error), \(error!.userinfo)")     }