var valuesCf = (from cfv in com.CustomFieldValues
                                join trCf in com.TempRapports on cfv.CustomField_id equals trCf.Ressource_Id
                                join trP in com.TempRapportsProjects on cfv.Project_id equals trP.Project_Id
                                where trP.ID == guidRap && trCf.ID == guidCf
                                group cfv by cfv.Project_id into grps
                                select new
                                {
                                    grps.Key,
                                    Values = grps.ToList()
                                }).ToDictionary(o => o.Key, o => o.Values);