domenu

  public class Startup
    {
     public void ConfigureServices(IServiceCollection services)
        {
            // ...
            services.AddControllers().AddJsonOptions(options =>
            {
                    options.JsonSerializerOptions.PropertyNamingPolicy = new SnakeCasePropertyNamingPolicy();
            });
            

domenu

	public static class HtmlExtensions
	{
	 public static IHtmlString DropDownListFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression,
                                                                          Dictionary<string, IEnumerable<SelectListItem>> selectList)
        {
            /*
             * <select name="tmodel">
             *   <optgroup label="Items">
             *   <option value="item">Item</option>
             * </select>