在ASP.NET Core Identity登录分部视图中获取关联表用户全名

问题原因 #

UserManager.GetUserAsync(User) 默认只会查询 ApplicationUser 表数据，不会自动加载关联的 Person 导航属性，导致 personResult.Person 为 null，访问 FullName 时触发"Object reference not set to an instance of an object."错误。

解决方案 #

方案1：自定义UserStore实现关联数据预加载 #

通过重写UserStore的查询方法，强制Include关联的Person表：

1. 创建自定义UserStore类：

public class CustomUserStore : UserStore<ApplicationUser>
{
    public CustomUserStore(DbContext context, IdentityErrorDescriber describer = null) 
        : base(context, describer)
    {
    }

    public override async Task<ApplicationUser> FindByIdAsync(string userId, CancellationToken cancellationToken = default)
    {
        return await Users.Include(u => u.Person)
                          .FirstOrDefaultAsync(u => u.Id == userId, cancellationToken);
    }

    public override async Task<ApplicationUser> FindByNameAsync(string normalizedUserName, CancellationToken cancellationToken = default)
    {
        return await Users.Include(u => u.Person)
                          .FirstOrDefaultAsync(u => u.NormalizedUserName == normalizedUserName, cancellationToken);
    }
}

2. 在Program.cs（或Startup.cs）中注册自定义UserStore：

services.AddIdentity<ApplicationUser, IdentityRole>()
        .AddUserStore<CustomUserStore>()
        .AddDefaultTokenProviders();

之后使用UserManager.GetUserAsync(User)就能自动获取关联的Person数据，无需修改分部视图代码。

方案2：在分部视图中直接通过DbContext加载关联数据 #

注入DbContext，显式Include Person表，并使用异步查询避免死锁：

修改Login Partial视图：

@using Microsoft.AspNetCore.Identity
@using Models;
@using System.Security.Claims;
@inject SignInManager<ApplicationUser> SignInManager
@inject ApplicationDbContext DbContext

<ul class="navbar-nav">
@if (SignInManager.IsSignedIn(User))
{
    <li class="nav-item">
        @{
            var userId = User.FindFirstValue(ClaimTypes.NameIdentifier);
            var user = await DbContext.Users.Include(u => u.Person)
                                            .FirstOrDefaultAsync(u => u.Id == userId);
            var fullName = user?.Person?.FullName ?? User.Identity?.Name;
        }
        <a class="nav-link text-dark" asp-area="Identity" asp-page="/Account/Manage/Index" title="Manage">Hello @fullName!</a>
    </li>
    <li class="nav-item">
        <form class="form-inline" asp-area="Identity" asp-page="/Account/Logout" asp-route-returnUrl="@Url.Page("/", new { area = "" })" method="post" >
            <button type="submit" class="nav-link btn btn-link text-dark">Logout</button>
        </form>
    </li>
}
else
{
    <li class="nav-item">
        <a class="nav-link text-dark" asp-area="Identity" asp-page="/Account/Register">Register</a>
    </li>
    <li class="nav-item">
        <a class="nav-link text-dark" asp-area="Identity" asp-page="/Account/Login">Login</a>
    </li>
}
</ul>

额外检查 #

确保数据库中ApplicationUser的PersonID字段已正确关联到Person表中存在的记录，避免因数据关联错误导致Person为null。

内容的提问来源于stack exchange，提问作者Reafidy