objective c - Retrieve Specific Object from Core Data -

i'm new core data , wondering if possible object based on it's attributes, more specifically, uniqueid assigned it. i'm trying because i'm interfacing web server, provides data updated core data. want search through each of web server objects, check timestamp, , if it's different, retrieve object core data, , update. i've looked @ using existingobjectwithid seems have know object i'm searching for, or id of object. i've thought sorting data in both arrays, , checking each simultaneously, didn't think viable.

here i'm doing far:

-(nsmutablearray*) updaterootbeers:(nsmutablearray*)webrootbeerlist{     nsmanagedobjectcontext* moc = [self managedobjectcontext];     nsfetchrequest* fetchrequest = [[nsfetchrequest alloc]initwithentityname:@"rootbeer"];     coredatarootbeerlist = [[moc executefetchrequest:fetchrequest error:nil]mutablecopy];     //check see if core data has data, if not, call function populate list     if (coredatarootbeerlist.count <=0) {         [self addrootbeertocoredata:webrootbeerlist];     }else{         //otherwise want update core data object if object data different.         for(rootbeer* currentrootbeer in webrootbeerlist){             rootbeer* mrootbeer = [moc existingobjectwithid:currentrootbeer error:nil];         }     }    } 

i've thought using nested loops check data in each array, seems poor coding. or thoughts great.

you want make nsfetchrequest. can set entity , provide predicate. simple , clean.