如何在视图中展示1对1关联数据并提交时更新对应数据表

1. 修复EnvelopeNumber显示空白的问题 #

问题根源是FindAsync方法不会自动加载EF Core的导航属性，导致member.Envelope为null，视图无法读取EnvelopeNumber。只需修改GET Edit方法，显式加载关联的Envelope：

修改MembersController的GET Edit方法 #

// GET: Members/Edit/5
public async Task<IActionResult> Edit(int? id)
{
    if (id == null)
    {
        return NotFound();
    }

    // 显式加载关联的Envelope导航属性
    var member = await _context.Member
        .Include(m => m.Envelope)
        .FirstOrDefaultAsync(m => m.MemberId == id);
    
    if (member == null)
    {
        return NotFound();
    }
    return View(member);
}

可选：完善1对1关联配置（推荐） #

当前模型缺少Envelope到Member的反向导航，建议补充以确保关联关系正确：

public class Envelope
{
    [Key]
    public int EnvelopeId { get; set; }

    [Required]
    [Display(Name = "Envelope Number")]
    public int EnvelopeNumber { get; set; }

    // 添加反向导航与外键
    [ForeignKey("Member")]
    public int MemberId { get; set; }
    public virtual Member? Member { get; set; }
}

2. 实现Member与Envelope独立提交更新 #

通过区分提交按钮的标识，让后端知道要更新哪个实体，或者拆分独立的提交Action，这里提供两种方案：

方案一：同一Action区分提交类型 #

步骤1：修改视图的提交按钮与表单

给两个提交按钮添加name属性，并在Envelope表单中加入EnvelopeId隐藏字段：

<!-- Member表单的提交按钮 -->
<input type="submit" name="submitAction" value="SaveMember" class="btn btn-primary" />

<!-- Envelope表单内容 -->
<form asp-action="Edit">
    <div asp-validation-summary="ModelOnly" class="text-danger"></div>
    <input type="hidden" asp-for="MemberId" />
    @if (Model.Envelope != null)
    {
        <input type="hidden" asp-for="Envelope.EnvelopeId" />
    }
    <!-- 其余Envelope字段代码不变 -->
    <input type="submit" name="submitAction" value="SaveEnvelope" class="btn btn-primary" />
</form>

步骤2：添加POST Edit方法处理不同提交

// POST: Members/Edit/5
[HttpPost]
[ValidateAntiForgeryToken]
public async Task<IActionResult> Edit(int id, string submitAction, Member member, Envelope envelope)
{
    if (id != member.MemberId)
    {
        return NotFound();
    }

    if (ModelState.IsValid)
    {
        try
        {
            if (submitAction == "SaveMember")
            {
                _context.Update(member);
            }
            else if (submitAction == "SaveEnvelope")
            {
                envelope.MemberId = id;
                if (envelope.EnvelopeId == 0)
                {
                    _context.Add(envelope);
                }
                else
                {
                    _context.Update(envelope);
                }
            }
            await _context.SaveChangesAsync();
        }
        catch (DbUpdateConcurrencyException)
        {
            if (!MemberExists(member.MemberId))
            {
                return NotFound();
            }
            throw;
        }
        return RedirectToAction(nameof(Index));
    }
    // 验证失败时重新加载Envelope返回视图
    member.Envelope = await _context.Envelope.FindAsync(envelope.EnvelopeId);
    return View(member);
}

private bool MemberExists(int id)
{
    return _context.Member.Any(e => e.MemberId == id);
}

方案二：拆分独立提交Action（更清晰） #

步骤1：修改视图表单的asp-action

<!-- Member表单 -->
<form asp-action="SaveMember">
    <!-- 内容不变 -->
</form>

<!-- Envelope表单 -->
<form asp-action="SaveEnvelope">
    <input type="hidden" asp-for="MemberId" />
    @if (Model.Envelope != null)
    {
        <input type="hidden" asp-for="Envelope.EnvelopeId" />
    }
    <!-- 其余Envelope字段代码不变 -->
</form>

步骤2：添加对应的提交Action

[HttpPost]
[ValidateAntiForgeryToken]
public async Task<IActionResult> SaveMember(Member member)
{
    if (ModelState.IsValid)
    {
        try
        {
            _context.Update(member);
            await _context.SaveChangesAsync();
        }
        catch (DbUpdateConcurrencyException)
        {
            if (!MemberExists(member.MemberId)) return NotFound();
            throw;
        }
        return RedirectToAction(nameof(Index));
    }
    member.Envelope = await _context.Envelope.FindAsync(member.MemberId);
    return View("Edit", member);
}

[HttpPost]
[ValidateAntiForgeryToken]
public async Task<IActionResult> SaveEnvelope(int memberId, Envelope envelope)
{
    if (ModelState.IsValid)
    {
        try
        {
            envelope.MemberId = memberId;
            if (envelope.EnvelopeId == 0)
            {
                _context.Add(envelope);
            }
            else
            {
                _context.Update(envelope);
            }
            await _context.SaveChangesAsync();
        }
        catch (DbUpdateConcurrencyException)
        {
            if (!EnvelopeExists(envelope.EnvelopeId)) return NotFound();
            throw;
        }
        return RedirectToAction(nameof(Index));
    }
    var member = await _context.Member.Include(m => m.Envelope).FirstOrDefaultAsync(m => m.MemberId == memberId);
    return View("Edit", member);
}

private bool EnvelopeExists(int id)
{
    return _context.Envelope.Any(e => e.EnvelopeId == id);
}

内容的提问来源于stack exchange，提问作者Bob H