.NET 6中在Repository类使用UserPrincipal出现空对象问题

在.NET 6环境下，原本在Controller中使用UserPrincipal功能正常，但将相关代码移至Models目录下的Repository类后，出现空引用错误。希望通过Repository类封装代码简化Controller逻辑，目前除UserPrincipal相关部分外其余功能均正常，求解决思路。

相关代码 #

using Directory.Services.AccountManagement;
using HumanResources.JobsContext;
using HumanResources.Models;
using HumanResources.Controllers;
using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;
using Microsoft.Data.SqlClient;

public class Repository : Controller
{
    [HttpPost]
    public ActionResult PostIndexInternal(IFormFile file, Job job)
    {       
        PrincipalContext pc = new PrincipalContext(ContextType.Domain, "PPS");
        UserPrincipal up = UserPrincipal.FindByIdentity(pc, User.Identity.Name);
        string first = up.GivenName;
        string last = up.Surname;
        string full = first + " " + last;
            
        if (file != null)
        {
            if (file.Length > 0)
            {
                //Get File Name
                var fileName = Path.GetFileName(file.FileName);
                //Get File Extension
                var fileExtension = Path.GetExtension(fileName);
                //Create New File Name based on AD Credentials
                var newFileName = String.Concat(user, fileExtension);

                //Creating new object on the database
                var fileObject = new InternalJob()
                {
                    IdJob = job.Id,
                    Title = job.Title,
                    EmployeeID = employeeID,
                    FileName = newFileName,
                    EmployeeName = user,
                    CurrentJobTitle = currentPosition,
                    DateApplied = DateTime.Now,
                    Active = true
                };
                using (var target = new MemoryStream())
                {
                    file.CopyTo(target);
                    fileObject.FileData = target.ToArray();
                }
                _hrContext.InternalJobs.Add(fileObject);
                _hrContext.SaveChanges();
                return RedirectToAction(nameof(JobsApplied));
            }
        }
        else if (file == null)
        {
            string msg = "Please do not forget to select and upload the Resume";
            return Json(msg);
        }

        return RedirectToAction(nameof(JobsApplied));
    }
}

//This would be in the HomeController
[HttpPost]
public IActionResult Example(IFormFile file, Job job)
{
    Repository repository = new Repository(_context);
    return repository.PostIndexInternal(IFormFile file, Job job);
}   

解决思路 #

• 取消Repository对Controller的继承
  Repository是业务/数据访问类，不应该继承Controller。Controller的User属性依赖于请求上下文，直接实例化Repository时该上下文未被初始化，导致User为null引发空引用。将Repository改为普通类，移除Controller继承关系。

• 从Controller传递用户身份信息
  在Controller中获取当前用户的User.Identity.Name，将其作为参数传入Repository的方法，而非在Repository内部直接访问User对象。示例修改：

  // Repository类修改为普通类
  public class Repository
  {
      private readonly HrContext _hrContext;
  
      public Repository(HrContext hrContext)
      {
          _hrContext = hrContext;
      }
  
      public ActionResult PostIndexInternal(IFormFile file, Job job, string userName)
      {
          PrincipalContext pc = new PrincipalContext(ContextType.Domain, "PPS");
          UserPrincipal up = UserPrincipal.FindByIdentity(pc, userName);
          // 后续逻辑保持不变
      }
  }
  
  // Controller调用时传递用户名
  [HttpPost]
  public IActionResult Example(IFormFile file, Job job)
  {
      Repository repository = new Repository(_context);
      return repository.PostIndexInternal(file, job, User.Identity.Name);
  }
  

• 添加空引用检查
  在使用UserPrincipal返回的对象前，必须检查是否为null，避免空引用异常：

  UserPrincipal up = UserPrincipal.FindByIdentity(pc, userName);
  if (up == null)
  {
      return new JsonResult("无法获取当前用户的AD信息");
  }
  string first = up.GivenName;
  string last = up.Surname;
  string full = first + " " + last;
  

• 可选：通过IHttpContextAccessor获取上下文（不推荐）
  如果必须在Repository中访问HttpContext，可通过依赖注入IHttpContextAccessor实现，但会增加类的耦合度，降低可测试性：

  1. 在Program.cs注册服务：

     builder.Services.AddHttpContextAccessor();
     

  2. Repository中注入并使用：

     public class Repository
     {
         private readonly HrContext _hrContext;
         private readonly IHttpContextAccessor _httpContextAccessor;
     
         public Repository(HrContext hrContext, IHttpContextAccessor httpContextAccessor)
         {
             _hrContext = hrContext;
             _httpContextAccessor = httpContextAccessor;
         }
     
         public ActionResult PostIndexInternal(IFormFile file, Job job)
         {
             var userName = _httpContextAccessor.HttpContext?.User?.Identity?.Name;
             if (string.IsNullOrEmpty(userName))
             {
                 return new JsonResult("用户未登录");
             }
             // 后续逻辑保持不变
         }
     }
     

内容的提问来源于stack exchange，提问作者sdw