ios - predicate is getting nil, nscoredata, objective -

what doing fetch data core data following

nsstring *str; nspredicate *predicate;  switch (typecube) {     case newcubes: {         str = [nsstring stringwithformat:@"type == %d",newcubes];         break;     }     case allcubes: {         str = [nsstring stringwithformat:@"type != %d",customcubes];         break;     }     case customcubes: {         str = [nsstring stringwithformat:@"type == %d",customcubes];         break;      } }  predicate = [nspredicate predicatewithformat:@"%@ , (accounts.keychainid == %@)", str, accountkeychainid]; 

however, result of predicate nil. following works

predicate = [nspredicate predicatewithformat:@"(type == %d) , (accounts.keychainid == %@)", type, accountkeychainid]; ( type either newcubes or allcubes or customcubes) 

please if have ideas. comments welcomed. thanks

there class called nscompoundpredicate allows construct predicates and, or , not operators. here need

[nscompoundpredicate andpredicatewithsubpredicates:@[predicate1, predicate2, etc.]]; 

so code --

nspredicate *predicate1; nspredicate *predicate;      switch (typecube) {         case newcubes: {             predicate1 = [nspredicate predicatewithformat:@"type == %d",newcubes];             break;         }         case allcubes: {             predicate1 = [nspredicate predicatewithformat:@"type != %d",customcubes];             break;         }         case customcubes: {             predicate1 = [nspredicate predicatewithformat:@"type == %d",customcubes];             break;          }     }     predicate = [nspredicate predicatewithformat:@"accounts.keychainid == %@", accountkeychainid];     [nscompoundpredicate andpredicatewithsubpredicates:@[predicate1, predicate]]; 

read more nscompountpredicates here: http://nshipster.com/nspredicate/