问在剃刀页面中的OnGetAsync中将值从另一个模型分配到另一个模型

EN

public class TestData
{
    [Key]
    public int TestID { get; set; }
    public string TestName { get; set; }
}

    private readonly Test.Models.TestContext _context;
    public EditModel(Test.Models.TestContext context)
    {
        _context = context;
    }
    [BindProperty]
    public TestData TestData { get; set; }

    [BindProperty]
    public InputModel Input { get; set; }

    public class InputModel
    {
        [Required, MaxLength(50), MinLength(3)]
        public string TestName { get; set; }
    }

    public async Task<IActionResult> OnGetAsync(int? id)
    {
        TestData = await _context.TestData.FirstOrDefaultAsync(m => m.TestID == id);
        Input.TestName = TestData.TestName; //Error Occurs here. TestData.TestName has value while debug.
        return Page();
    }

    public async Task<IActionResult> OnPostAsync()
    {
        TestData.TestName = Input.TestName;
        _context.Attach(TestData).State = EntityState.Modified;
        await _context.SaveChangesAsync();
        return RedirectToPage("./Index");
    }