C# ASP.NET MVC birebir ilişkiye sahip sınıfları aynı aksiyonda oluşturup ilişkilendirmek mümkün mü?

public async Task<IActionResult> Create(CreatePostVM viewModel)
        {
            if (ModelState.IsValid)
            {
                var user = await _userManager.GetUserAsync(User);

                Car car = new Car
                {
                    Make = viewModel.Make,
                    Model = viewModel.Model,
                    Year = viewModel.Year,
                    Kilometer = viewModel.Kilometer,
                    HorsePower = viewModel.HorsePower,
                    LocationCountry = viewModel.LocationCountry,
                    LocationCity = viewModel.LocationCity,
                    CategoryId = viewModel.CategoryId,
                    FuelTypeId = viewModel.FuelTypeId,
                    TransmissionTypeId = viewModel.TransmissionTypeId,
                    CarExtras = new List<CarExtra>(),
                    Images = new List<Image>(),
                };

                Post post = new Post()
                {
                    Title = viewModel.Title,
                    Description = viewModel.Description,
                    Price = viewModel.Price,
                    CoverImage = viewModel.CoverImage,
                    CreatorId = user.Id,
                    Car = car
                };

             

                if (viewModel.SelectedExtras != null)
                {
                    foreach (var extra in viewModel.SelectedExtras)
                    {
                        var carExtra = new CarExtra()
                        {
                            CarId = post.CarId,
                            ExtraId = extra
                        };
                        post.Car.CarExtras.Add(carExtra);
                    }
                }

                if (viewModel.SelectedImages != null && viewModel.SelectedImages.Count > 0)
                {
                    foreach (var file in viewModel.SelectedImages)
                    {
                        var fileName = Path.GetFileName(file.FileName);
                        var fileExtension = Path.GetExtension(fileName);
                        var uniqueFileName = Guid.NewGuid().ToString() + fileExtension;
                        var filePath = Path.Combine(Directory.GetCurrentDirectory(), "wwwroot/images", uniqueFileName);
                        using (var stream = new FileStream(filePath, FileMode.Create))
                        {
                            file.CopyTo(stream);
                        }
                        var image = new Image()
                        {
                            CarId = post.CarId,
                            Path = fileName
                        };
                        post.Car.Images.Add(image);
                    }
                }

                _db.Posts.Add(post);
             

                await _db.SaveChangesAsync();
            }
            else
            {
                var errors = ModelState.Select(x => x.Value.Errors)
                           .Where(y => y.Count > 0)
                           .ToList();
                return BadRequest(errors);
            }


            return RedirectToAction("GetAll");
        }