asp.net core实现文件上传功能

 public class UserViewModel
{
  [Required]
  [Display(Name = "姓名")]
  public string Name { get; set; }

  [Required]
  [Display(Name = "身份证")]
  [RegularExpression(@"^(\d{15}$|^\d{18}$|^\d{17}(\d|X|x))$", ErrorMessage = "身份证号不合法")]
  public string IdNum { get; set; }

  public string IdCardImgName { get; set; }

  [Required]
  [Display(Name = "身份证附件")]
  [FileExtensions(Extensions = ".jpg,.png", ErrorMessage = "图片格式错误")]
  public IFormFile IdCardImg { get; set; }
} 

 @model UserViewModel

<form asp-controller="Home" role="form" asp-action="New" enctype="multipart/form-data" method="post">
  <div class="form-group">
    <label asp-for="Name"></label>
    <input type="text" class="form-control" asp-for="Name" />
  </div>
  <div class="form-group">
    <label asp-for="IdNum"></label>
    <input type="text" class="form-control" asp-for="IdNum" />
  </div>
  <div class="form-group">
    <label asp-for="IdCardImg"></label>
    <input type="file" asp-for="IdCardImg" />
    <p class="help-block">上传。</p>
  </div>
  <button type="submit" class="btn btn-default">提交</button>
</form> 

 [HttpPost]
public IActionResult New([FromServices]IHostingEnvironment env, [FromServices]AppDbContext dbContext, UserViewModel user) {
  var fileName = Path.Combine("upload", DateTime.Now.ToString("MMddHHmmss") + ".jpg");
  using (var stream = new FileStream(Path.Combine(env.WebRootPath, fileName), FileMode.CreateNew)) {
    user.IdCardImg.CopyTo(stream);
  }

  var users = dbContext.Set<User>();
  var dbUser = new User() {
    Name = user.Name,
    IdCardNum = user.IdNum,
    IdCardImgName = fileName
  };
  users.Add(dbUser);
  dbContext.SaveChanges();

  return RedirectToAction(nameof(Index));
}