iphone - Core data relation with predicates -

i have entity car , entity race. both entities has attribute called carclass. problem want create relation between them on joining carclass.

basically want create relation in core data represents possible competitors of race, depending on carclass, in other words if create race specific carclass , call competitors on race want list of cars same carclass.

my question is, possible create using core data relations, i'm thinking adding nspredicate relation.

thanks in advance.

update

i think didn't explained want achieve.

car{   carclass:string }  race{  carclass:string  competitors<-->>cars.carclass == carclass } 

and competitors should fetched automatically, don't have add manually competitors, should retrieve matching cars cars model.

the simplest model this:

carclass{     name:string     race<-->race.carclass     cars<-->>car.carclass }  car{     name:string     carclass<<-->carclass.cars }  race{     name:string     carclass<-->>carclass.race } 

don't think sql terms, think of in object terms. each entity should represent real-world object, event or condition want simulate. relationships between objects should mimic real-world relationships. if both race , car real-world things have common relationship carclass condition put in model.

unlike sql, object models can arbitrarily complex , can contain behaviors well. not stuck tables, columns , rows.

update:

(see update in op reference)

when find putting same attribute value in 2 or more different entities, means need create new entity model value.

in case, though in terms of data carclass value string logically separate thing altogether related both race , car objects. so, accurately model it, need provide separate entity it. in addition, need model competitors need model looks like:

carclass{     class:string     race<-->race.carclass     cars<-->>car.carclass }  car{     name:string     carclass<<-->carclass.cars     competitor<-->>competitor.car }  race{     name:string     carclass<-->carclass.race }  competitor{   name:string   car<-->car.competitor } 

(note model assumes races defined carclass , not individual vehicles or drivers.)

so, find competitors of particular race, walk race.carclass.cars.competitor.

this isn't want can idea or how use entities , relationships model real-world objects, events or conditions , linkages between them.