How to map multiple entities to one class in Mapster

Question

In AutoMapper, we can map multiple entities to one, but can't impl in mapster. Automapper demo code:

Entity:

var users = await _userManager.Users
            .AsNoTracking()
            .ProjectTo<UserDto>(new { roles = _roleManager.Roles })              
            .ToListAsync();

AutoMapper config:

IQueryable<IdentityRole> roles = null;
        CreateMap<User, UserDto>()
            .ForMember(x => x.Roles, opt => 
                opt.MapFrom(src => 
                    src.Roles
                        .Join(roles, a => a.RoleId, b => b.Id, (a, b) => b.Name)
                        .ToList()
                )
            );

There is no parameter in Mapster Querable.ProjectTo() method. Who can help me see what I should do? Thanks.