ASP.NET Core 6 MVC项目SqlNullValueException报错求助

我正在开发ASP.NET Core 6 MVC项目，遇到了SqlNullValueException错误，错误信息为：Data is Null. This method or property cannot be called on Null values。这是我的作业，已经尝试修改ClubController和ClubRepository代码，但问题仍未解决，相关代码如下：

ClubController 代码 #

using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;
using webHomework.Data;
using webHomework.Interfaces;
using webHomework.Models;
using webHomework.ViewModels;

namespace webHomework.Controllers
{
    public class ClubController : Controller
    {
        private readonly IClubRepository _clubRepository;
        private readonly IPhotoService _photoService;

        public ClubController(IClubRepository clubRepository, IPhotoService photoService)
        {
            _clubRepository = clubRepository;
            _photoService = photoService;
        }      

        public async Task<IActionResult> Index()
        {
            IEnumerable<Club> clubs = await _clubRepository.GetAll();
            return View(clubs);
        }

        public async Task<IActionResult> Detail(int id)
        {
            Club club = await _clubRepository.GetByIdAsync(id);
            return View(club);
        }

        public IActionResult Create()
        {
            return View();
        }

        [HttpPost]
        public async Task<IActionResult> Create(CreateClubViewModel clubVM)
        {
            if (ModelState.IsValid)
            {
                var result = await _photoService.AddPhotoAsync(clubVM.Image);

                var club = new Club
                {
                    Title = clubVM.Title,
                    Description = clubVM.Description,
                    Image = result.Url.ToString(),
                    Address = new Address
                    {
                        Street = clubVM.Address.Street,
                        City = clubVM.Address.City,
                        State = clubVM.Address.State,
                    }
                };

                _clubRepository.Add(club);

                return RedirectToAction("Index");
            }
            else
            {
                ModelState.AddModelError("", "Photo upload failed");
            }

            return View(clubVM);
        }
    }
}

ClubRepository 代码 #

using Microsoft.EntityFrameworkCore;
using webHomework.Data;
using webHomework.Interfaces;
using webHomework.Models;

namespace webHomework.Repository
{
    public class ClubRepository : IClubRepository
    {
        private readonly ApplicationDbContext _context;

        public ClubRepository (ApplicationDbContext context)
        {
            _context = context;
        }

        public bool Add(Club club)
        {
            _context.Add(club);
            return Save();
        }

        public bool Delete(Club club)
        {
            _context.Remove(club);
            return Save();
        }

        public async Task<IEnumerable<Club>> GetAll()
        {
            return await _context.Clubs.ToListAsync();
        }

        public async Task<Club> GetByIdAsync(int id)
        {
            return await _context.Clubs.Include(i => i.Address).FirstOrDefaultAsync(i => i.Id == id);
        }

        public async Task<IEnumerable<Club>> GetClubByCity(string city)
        {
            return await _context.Clubs.Where(c => c.Address.City.Contains(city)).ToListAsync();
        }

        public bool Save()
        {
            var saved = _context.SaveChanges();
            return saved > 0 ? true : false;
        }

        public bool Update(Club club)
        {
            _context.Update(club);
            return Save();
        }
    }
}

问题原因分析 #

1. 实体类与数据库字段可空性不匹配：如果Club或Address实体类中存在非可空属性（比如public string City { get; set; }），但数据库中对应字段允许为NULL，EF Core读取时会抛出该异常。
2. 查询未关联导航属性：GetAll方法没有IncludeAddress，如果数据库中某条Club记录的Address为NULL，而实体类中Address属性是非可空的，会触发错误。
3. 空引用访问：GetClubByCity方法直接访问c.Address.City，如果Address本身为NULL，会引发空引用，同时如果City字段为NULL且实体类属性非可空，也会触发SqlNullValueException。

解决方案 #

1. 修正实体类属性可空性
   打开Club和Address实体类，将允许为空的属性改为可空类型：

   // Address类示例
   public class Address
   {
       public int Id { get; set; }
       public string? Street { get; set; }
       public string? City { get; set; }
       public string? State { get; set; }
       public Club? Club { get; set; }
   }
   
   // Club类示例
   public class Club
   {
       public int Id { get; set; }
       public string Title { get; set; }
       public string Description { get; set; }
       public string Image { get; set; }
       public Address? Address { get; set; } // 如果允许Club没有Address，改为可空
   }
   

2. 完善仓储查询方法

   • 更新GetAll方法，关联Address：

     public async Task<IEnumerable<Club>> GetAll()
     {
         return await _context.Clubs.Include(i => i.Address).ToListAsync();
     }
     

   • 更新GetClubByCity方法，增加空值判断：

     public async Task<IEnumerable<Club>> GetClubByCity(string city)
     {
         return await _context.Clubs
             .Include(i => i.Address)
             .Where(c => c.Address != null && c.Address.City != null && c.Address.City.Contains(city))
             .ToListAsync();
     }
     

3. 检查数据库数据
   确认数据库中Clubs和Addresses表的关联数据，避免NULL值对应到实体类的非可空属性。如果新增数据时允许部分字段为空，确保实体类属性已设置为可空。

内容的提问来源于stack exchange，提问作者Lambersonistaken