<Project Sdk="Microsoft.NET.Sdk.Web">

  <PropertyGroup>
    <TargetFramework>netcoreapp3.1</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="AutoMapper" Version="9.0.0" />
    <PackageReference Include="AutoMapper.Extensions.Microsoft.DependencyInjection" Version="7.0.0" />
  </ItemGroup>


</Project>

    public class User
    {
        public int Id { get; set; }

        public string Name { get; set; }

        public int Age { get; set; }

        public string Remark { get; set; }

        public int DepartmentId { get; set; }

        public Department DepartmentInfo { get; set; }
    }

    public class Department
    {
        public int Id { get; set; }

        public string Name { get; set; }

        public string Remark { get; set; }
    }

    public class UserDto
    {
        public int Id { get; set; }

        public string Name { get; set; }
    }

    public class UserViewModel
    {
        public int Id { get; set; }

        public string Name { get; set; }

        public int Age { get; set; }

        public string Remark { get; set; }

        public int DepartmentId { get; set; }

        public string DepartmentName { get; set; }
    }

    public class UserMapper : Profile
    {
        public UserMapper()
        {
            CreateMap<UserDto, User>();
            CreateMap<User, UserViewModel>()
                .BeforeMap((u, v) => u.Remark = "Good")
                .ForMember(v => v.DepartmentId, u => u.MapFrom(user => user.DepartmentId))
                .ForMember(v => v.DepartmentName, u => u.MapFrom(user => user.DepartmentInfo.Name))
                .AfterMap((u, v) => u.Age++);
        }
    }

        public void ConfigureServices(IServiceCollection services)
        {
            // ...
            services.AddAutoMapper(typeof(UserMapper));
            // ...
        }    

    [Route("api/[controller]/[action]")]
    [ApiController]
    public class UserController : ControllerBase
    {
        private readonly IMapper _mapper;

        public UserController(IMapper mapper)
        {
            _mapper = mapper;
        }

        [ActionName("dto")]
        [HttpGet]
        public IActionResult DtoToEntity()
        {
            var userDto = new UserDto() { Id = 1, Name = "Bill" };
            var userEntity = _mapper.Map<UserDto, User>(userDto);

            JsonResult result = new JsonResult(userEntity);
            return result;
        }

        [ActionName("vo")]
        [HttpGet]
        public IActionResult EntityToViewModel()
        {
            var department = new Department() { Id = 101, Name = "Market" };
            var user = new User() { Id = 1, Name = "Bill", Age = 25, DepartmentId = 101, DepartmentInfo = department };
            var viewModel = _mapper.Map<User, UserViewModel>(user);

            JsonResult result = new JsonResult(viewModel);
            return result;
        }

    }