core data - Relationship between logged in Users stackmob -

i use stackmob backend , coredata.

i have "user" , "sport" objects (user <<-> sport). users must have sport object require. if user logged in, others can't use sport object until users logged out. example, want change sport. when change have crash. because, sport have reverse relation users. seems can't use same object between users. how possible? , how resolve situation?

crashed here(smincrementalstore.m):

- (id)newvalueforrelationship:(nsrelationshipdescription *)relationship               forobjectwithid:(nsmanagedobjectid *)objectid                   withcontext:(nsmanagedobjectcontext *)context                         error:(nserror *__autoreleasing *)error 

with crashlog:

*

** terminating app due uncaught exception 'smexceptionincompatibleobject', reason: 'no attribute found entity user maps primary key on stackmob. attribute name should match 1 of following formats: lowercasedentitynameid or lowercasedentityname_id. if managed object subclass user inherits smusermanagedobject, meaning intended define user objects, may return either of above formats or whatever lowercase string optional underscores matches primary key field on stackmob.' * first throw call stack: (0x3916c2a3 0x3307e97f 0x3916c1c5 0x21c6e9 0x35a45bf3 0x341234b7 0x341279f7 0x35a359e7 0x35a45855 0x35a1d951 0x359edd4d 0x359ee3d5 0x3910e341 0x38e5a07b 0x38df2443 0x38e59f5d 0x35a31b57 0x10dfbd 0x1fdef9 0x3412411f 0x341234b7 0x341281bd 0x3913ff3b 0x390b2ebd 0x390b2d49 0x36c662eb 0x3b5382f9 0xd4ed5 0x32fc5b20)