.NET Core中为模型创建控制器后遭遇实体上下文问题

看起来你在为Event模型搭建控制器后遇到了问题，我先帮你梳理下现有代码，并给出一些常见问题的排查方向——虽然你没明确说明具体的报错或异常现象，但从代码里能看到几个潜在的问题点：

1. 核心模型代码 #

Event模型 #

public class Event { 
    public int ID { get; set; } 
    [Required] 
    public string Title { get; set; } 
    [Required] 
    public string Description { get; set; } 
    [DataType(DataType.Date)] 
    [Required] 
    public DateTime Date { get; set; } 
    public Subcategory Subcategory { get; set; } 
    public int SubcategoryID { get; set; } 
    public Place Place { get; set; } 
    public int PlaceID { get; set; } 
    public Organisator Organisator { get; set; } 
    public int OrganisatorID { get; set; } 
    public ICollection<User_link> User_link { get; set; } 
}

Place模型（一对多关联示例） #

Subcategory、Place、Organisator均与Event为一对多关联，这里以Place为例：

public class Place { 
    public int ID { get; set; } 
    [Required] 
    public string Title { get; set; } 
    [Required] 
    public string Address { get; set; } 
    [Required] 
    public string Call_number { get; set; } 
    public string Email { get; set; } 
    public string Vk { get; set; } 
    public string Facebook { get; set; } 
    public ICollection<Event> Event { get; set; } 
}

2. EventsController代码 #

public class EventsController : Controller { 
    private readonly ApplicationDbContext _context; 
    public EventsController(ApplicationDbContext context) { 
        _context = context; 
    } 

    // GET: Events 
    public async Task<IActionResult> Index() { 
        var applicationDbContext = _context.Event.Include(@ => @.Organisator).Include(@ => @.Place).Include(@ => @.Subcategory); 
        return View(await applicationDbContext.ToListAsync()); 
    } 

    // GET: Events/Details/5 
    public async Task<IActionResult> Details(int? id) { 
        if (id == null) { 
            return NotFound(); 
        } 
        var @event = await _context.Event 
            .Include(@ => @.Organisator) 
            .Include(@ => @.Place) 
            .Include(@ => @.Subcategory) 
            .SingleOrDefaultAsync(m => m.ID == id); 
        if (@event == null) { 
            return NotFound(); 
        } 
        return View(@event); 
    } 

    // GET: Events/Create 
    public IActionResult Create() { 
        ViewData["OrganisatorID"] = new SelectList(_context.Organisator, "ID", "Title"); 
        ViewData["PlaceID"] = new SelectList(_context.Place, "ID", "Address"); 
        ViewData["SubcategoryID"] = new SelectList(_context.Subcategory, "ID", "Title"); 
        return View(); 
    } 

    // POST: Events/Create 
    // To protect from overposting attacks, please enable the specific properties you want to bind to, for 
    // more details see http://go.microsoft.com/fwlink/?LinkId=317598. 
    [HttpPost] 
    [ValidateAntiForgeryToken] 
    public async Task<IActionResult> Create([Bind("ID,Title,Description,Date,SubcategoryID,PlaceID,OrganisatorID")] Event @event) { 
        if (ModelState.IsValid) { 
            _context.Add(@event); 
            await _context.SaveChangesAsync(); 
            return RedirectToAction(nameof(Index)); 
        } 
        ViewData["OrganisatorID"] = new SelectList(_context.Organisator, "ID", "Title", @event.OrganisatorID); 
        ViewData["PlaceID"] = new SelectList(_context.Place, "ID", "Address", @event.PlaceID); 
        ViewData["SubcategoryID"] = new SelectList(_context.Subcategory, "ID", "Title", @event.SubcategoryID); 
        return View(@event); 
    } 

    // GET: Events/Edit/5 
    public async Task<IActionResult> Edit(int? id) { 
        if (id == null) { 
            return NotFound(); 
        } 
        var @event = await _context.Event.SingleOrDefaultAsync(m => m.ID == id); 
        if (@event == null) { 
            return NotFound(); 
        } 
        ViewData["OrganisatorID"] = new SelectList(_context.Organisator, "ID", "Title", @event.OrganisatorID); 
        ViewData["PlaceID"] = new SelectList(_context.Place, "ID", "Address", @event.PlaceID); 
        ViewData["SubcategoryID"] = new SelectList(_context.Subcategory, "ID", "Title", @event.SubcategoryID); 
        return View(@event); 
    } 

    // POST: Events/Edit/5 
    // To protect from overposting attacks, please enable the specific properties you want to bind to, for 
    // more details see http://go.microsoft.com/fwlink/?LinkId=317598. 
    [HttpPost] 
    [ValidateAntiForgeryToken] 
    public async Task<IActionResult> Edit(int id, [Bind("ID,Title,Description,Date,SubcategoryID,PlaceID,OrganisatorID")] Event @event) { 
        if (id != @event.ID) { 
            return NotFound(); 
        } 
        if (ModelState.IsValid) { 
            try { 
                _context.Update(@event); 
                await _context.SaveChangesAsync(); 
            } catch (DbUpdateConcurrencyException) { 
                if (!EventExists(@event.ID)) { 
                    return NotFound(); 
                } else { 
                    throw; 
                } 
            } 
            return RedirectToAction(nameof(Index)); 
        } 
        ViewData["OrganisatorID"] = new SelectList(_context.Organisator, "ID", "Title", @event.OrganisatorID); 
        ViewData["PlaceID"] = new SelectList(_context.Place, "ID", "Address", @event.PlaceID); 
        ViewData["SubcategoryID"] = new SelectList(_context.Subcategory, "ID", "Title", @event.SubcategoryID); 
        return View(@event); 
    } 

    // GET: Events/Delete/5 
    public async Task<IActionResult> Delete(int? id) { 
        if (id == null) { 
            return NotFound(); 
        } 
        var @event = await _context.Event 
            .Include(@ => @.Organisator) 
            .Include(@ => @.Place) 
            .Include(@ => @.Subcategory) 
            .SingleOrDefaultAsync(m => m.ID == id); 
        if (@event == null) { 
            return NotFound(); 
        } 
        return View(@event); 
    } 

    // POST: Event
}

3. 重点排查与修复建议 #

（1）控制器代码不完整 #

你的Delete动作的POST方法只写了注释就中断了，这会导致删除功能完全无法使用，补全代码如下：

[HttpPost, ActionName("Delete")]
[ValidateAntiForgeryToken]
public async Task<IActionResult> DeleteConfirmed(int id)
{
    var @event = await _context.Event.FindAsync(id);
    if (@event == null)
    {
        return NotFound();
    }
    _context.Event.Remove(@event);
    await _context.SaveChangesAsync();
    return RedirectToAction(nameof(Index));
}

// 补全缺失的EventExists方法
private bool EventExists(int id)
{
    return _context.Event.Any(e => e.ID == id);
}

（2）模型命名冲突风险 #

Event是C#的关键字，虽然你用@event来规避编译错误，但长期来看容易引发混淆，建议把模型重命名为EventItem或者EventEntity这类更清晰的名称。

（3）关联数据加载遗漏 #

在Edit的GET方法中，你没有加载Organisator、Place、Subcategory这些关联实体，如果视图需要显示这些关联数据（比如编辑页面要显示场地名称），会直接抛出空引用异常，修改代码如下：

var @event = await _context.Event
    .Include(e => e.Organisator)
    .Include(e => e.Place)
    .Include(e => e.Subcategory)
    .SingleOrDefaultAsync(m => m.ID == id);

（4）下拉列表显示字段不合理 #

在Create和Edit中，Place的下拉列表用了Address作为显示文本，用户选择时可能更希望看到场地的Title，可以根据需求调整：

ViewData["PlaceID"] = new SelectList(_context.Place, "ID", "Title", @event.PlaceID);

（5）ModelState验证排查 #

如果创建/编辑时出现页面回退但没有提示，建议在视图中添加验证摘要，方便查看具体的验证失败原因：

@Html.ValidationSummary(true, "", new { @class = "text-danger" })

如果这些建议没解决你的问题，欢迎补充具体的报错信息、异常现象或者功能失效的场景，我再帮你深入排查！

内容的提问来源于stack exchange，提问作者uldrsk