API - Blazor 服务器 - 外键 ICollection 始终为空 - EF 核心

Question

我是 API 和 Blazor 的新手，我正在尝试遵循此示例 (https://docs.microsoft.com/en-us/aspnet/core/data/ef-rp/crud?view=aspnetcore-5.0)

您可以在下面看到我的模型和代码。

型号：

public class Student {
    public int StudentId { get; set; }

    public string FirstName { get; set; }

    public string LastName { get; set; }

    public DateTime EnrollmentDate { get; set; }

    [JsonIgnore]
 public virtual ICollection<Enrollment> Enrollments { get; set;}
}

API 控制器：

[HttpGet]
    [Route("{id:int}")]
    public async Task<ActionResult<Student>> GetStudent(int id)
    {
        try
        {
            var result = await context.Students
                .Include(s => s.Enrollments)
                    .ThenInclude(e => e.Course)
                .AsNoTracking()
                .FirstOrDefaultAsync(m => m.StudentId == id);

            //var result = await context.Students
            //    .Where(s => s.StudentId == id)
            //    .Select(s => new
            //    {
            //        Student = s,
            //        Enrollment = s.Enrollments

            //    })
            //    .FirstOrDefaultAsync();

            if (result == null)
            {
                return NotFound();
            }
            return Ok(result);
        }
        catch (Exception)
        {
            return StatusCode(StatusCodes.Status500InternalServerError, "Error receiving data from database");
        }
    }

Blazor 服务器中的学生模型

public class Student
{
    public int StudentId { get; set; }

    public string FirstName { get; set; }

    public string LastName { get; set; }

    public DateTime EnrollmentDate { get; set; }

    [JsonIgnore]
    public virtual ICollection<Enrollment> Enrollments { get; set; }
}

我的 Blazor 学生群：

public class StudentDetailsBase : ComponentBase
{
    [Inject]
    public IEnrollmentService EnrollmentService { get; set; }

    [Inject]
    public IStudentService StudentService { get; set; }

    public Student Student { get; set; }
    public List<Enrollment> Enrollments { get; set; }

    //public ICollection<Student> Student { get; set; }

    [Parameter]
    public string Id { get; set; }

    protected override async Task OnInitializedAsync()
    {
        Id = Id ?? "1";
        Student = await StudentService.GetStudent(int.Parse(Id));
        Enrollments = (await EnrollmentService.GetEnrollmentBySID(int.Parse(Id))).ToList();
        //Student = (await StudentService.GetStudent(int.Parse(Id))).ToList();
    }
}

还有我的学生显示页面：

@if (Student == null)
    {
        <p>Loading ...</p>
    }
    else
    {
        <div>
            <table class="table">
                <thead>
                    <tr>
                        <th>First Name</th>
                        <th>Last Name</th>
                        <th>Enrollment Date</th>
                        <th>All enrollments</th>
                    </tr>
                </thead>
                <tbody>
                    <tr>
                        <td>@Student.FirstName</td>
                        <td>@Student.LastName</td>
                        <td>@Student.EnrollmentDate</td>
                        @foreach (var i in Student.Enrollments)
                        {
                            <td>@i.Course.Title</td>
                            <td>@i.Grade</td>
                        }
                    </tr> 
                </tbody>
            </table>
        </div>
    }

我试图用谷歌搜索这个问题，但我不知道我做错了什么。 我的 Student.Enrollments 始终为 null。 这会导致我的 Blazor 服务器抛出错误。

当我使用 Postman 测试我的 API 时，它工作正常。

希望有人能指出我如何解决这个问题的正确方向。

谢谢。 亲切的问候。