gorm - Grails discriminator -column of ids point to two different classes -

can't seem figure out how choose column points using discriminators

class groups{     string groupcode   static mapping{       discriminator value:"1", formula:"case         when group_codein ('slt','ddg') 0 else 1 end", type:"integer"    }   }  class supportlivetraining extends groups{          static mapping{              discriminator value:"0"         }      staffsupportgroup group    }   class purchasesupport extends groups{          static mapping{              discriminator value:"1"       }   customersupportgroup group  } 

i error "return type of ...supportlivetraining getgroup() incompatible groups.getgroup()"