在 Blazor 中使用 EF Core 更新具有多个联接表的表格，需要按照以下步骤操作：

1. 如果还没有，则添加对 EF Core 和所需 NuGet 包的引用
2. 在 Startup.cs 中启用 EF Core 并添加所需数据库上下文，例如：

services.AddDbContext(options => 
    options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));

3. 创建所需实体模型，例如：

public class Student
{
    public int Id { get; set; }
    public string Name { get; set; }

    public int ClassId { get; set; }
    public Class Class { get; set; }

    public int DepartmentId { get; set; }
    public Department Department { get; set; }
}

public class Class
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class Department
{
    public int Id { get; set; }
    public string Name { get; set; }
}

4. 在 DbContext 中添加以下 DbSet 属性：

public DbSet Students { get; set; }
public DbSet Classes { get; set; }
public DbSet Departments { get; set; }

5. 创建一个 ViewModel 来处理更新/编辑表单的输入和结果，例如：

public class EditStudentViewModel
{
    private readonly MyDbContext _context;
    
    public EditStudentViewModel(MyDbContext context)
    {
        _context = context;
    }

    public Student Student { get; private set; }
    public List Classes { get; private set; }
    public List Departments { get; private set; }

    public async Task LoadAsync(int id)
    {
        Student = await _context.Students.FindAsync(id);
        Classes = await _context.Classes.ToListAsync();
        Departments = await _context.Departments.ToListAsync();
    }

    public async Task SaveAsync()
    {
        await _context.SaveChangesAsync();
    }
}

6. 在组件中使用 ViewModel，例如：

@page "/edit-student/{id}"
@inject MyDbContext Context

Edit Student