ios - NSSortDescriptor - Sort descriptor based on another array -

i hava core data application. , want fetch 1 kind of object, user. user have property userid.

i have array userids, [1, 4, 3, 5]. , create nssortdescriptor sorts userobjects based on order of userids in array.

is possible, , how should that?

update

i have tried following.

1. i added transformable property user object, store user ids array.

2. i have tried following sort descriptor:

   sortdescriptor = [[nssortdescriptor alloc] initwithkey:@"userid" ascending:yes     comparator:^nscomparisonresult(id obj1, id obj2) {     nsuinteger idx1 = [self.user.followingids indexofobject:[obj1 valueforkey:@"userid"]];     nsuinteger idx2 = [self.user.followingids indexofobject:[obj2 valueforkey:@"userid"]];     return idx1 - idx2; }]; 

and i'm getting following error:

serious application error.  exception caught during core data change processing.   bug within observer of nsmanagedobjectcontextobjectsdidchangenotification.   [<__nscfnumber 0xa337400> valueforundefinedkey:]: class not key value coding-compliant  key userid. userinfo {     nstargetobjectuserinfokey = 2502;     nsunknownuserinfokey = userid; } *** terminating app due uncaught exception 'nsunknownkeyexception', reason:    '[<__nscfnumber 0xa337400> valueforundefinedkey:]: class not key value coding-   compliant key userid.' 

update 2

would add relationship followers between user objects. ideas how relationship should look? see attached image. correct?

this can not done sort descriptor, have apply custom comparator function after fetching results:

nsarray *userids = ...; // e.g. @[@1, @4, @3, @5] nsarray *results = ...; // result of fetch request nsarray *sorted = [results sortedarrayusingcomparator:^nscomparisonresult(id obj1, id obj2) {     nsuinteger idx1 = [userids indexofobject:[obj1 valueforkey:@"userid"]];     nsuinteger idx2 = [userids indexofobject:[obj2 valueforkey:@"userid"]];     return idx1 - idx2; }];