public IActionResult Create([FromBody]CreateOrderDto dto)
{
 if(ModelState.IsValid)
 {
  //TODO:...
 }
}

public class XcHttpResult
{
 public string Msg { get; set; }
 public bool Result { get; set; }
}

public class XcActionFilter : IActionFilter
{
 public void OnActionExecuting(ActionExecutingContext context)
 {
 if (!context.ModelState.IsValid)
 {
  XcHttpResult result = new XcHttpResult() { Result = false };
  foreach (var item in context.ModelState.Values)
  {
  foreach (var error in item.Errors)
  {
   result.Msg += error.ErrorMessage + "|";
  }
  }
  context.Result = new JsonResult(result);
 }
 }
 public void OnActionExecuted(ActionExecutedContext context)
 {
 }
}

public void ConfigureServices(IServiceCollection services)
{
 services.AddMvc(options =>
 {
 options.Filters.Add<XcActionFilter>();
 });
}

public class CreateOrderDto
{
 [Required(ErrorMessage = "商品ID不得为空")]
 public string ProductId { get; set; }
 [Required(ErrorMessage = "购买商品数量不得为空")]
 [Range(1, 999, ErrorMessage = "购买商品数量必须介于1~999之间")]
 public int Number { get; set; } = 0;
 [Required(ErrorMessage = "用户ID不得为空")]
 public string UserId { get; set; }
}