在哪里包含对象列表

Question

我是EntityFrameWorkCore和ASP.NET Core的新手，我有以下问题。 我有2张桌子，文凭和老师，我正在尝试选择具有授课名称的文凭。我使用join（）来内部加入2个表，但我不断收到错误。我该如何实现这一目标，还是还有其他方法可以做到这一点？ 使用ASP.NET Core 5.0和EntityFrameWorkCore 5.0

模型

public class Diploma
{
    public Diploma(){
        this.Status = "Pending";
    }
    public int Id { get; set; }
    [Required]     
    [Display(Name = "Title")]
    public string Title { get; set; }
    [Display(Name = "Teachers")]
    public List<Teacher> Teachers { get; set; }
    [Display(Name = "Description")]
    public string Description { get; set; }
    [Display(Name = "Student Name")]
    public string StudentName { get; set; }
    public string Status { get; set; }
    [Display(Name = "FilePath")]
    public string FilePath { get; set; }
}

public class Teacher
{
    public int TeacherId { get; set; }
    [Display(Name = "TeacherName")]
    public string Name { get; set; }
    public int DiplomaId { get; set; }
    public Diploma Diploma { get; set; }
}

sqlrepository

public IEnumerable<Diploma> GetAllDiplomasForTeachers(string username)
{
    Teacher t = new Teacher();
    t.Name = username;            

    var query = context.Diplomas.Join(
        context.Teachers,
        diploma => diploma.Id,
        teacher => teacher.DiplomaId,
        (diploma, teacher) => new Diploma
        {
            Id = diploma.Id,
            Title = diploma.Title,
            Description = diploma.Description,
            StudentName = diploma.StudentName,
            Teachers = context.Teachers.ToList<Teacher>(),
            Status = diploma.Status,
            FilePath = diploma.FilePath
        }
        ).Where(a => a.Teachers.Contains(t)); //This line produces[enter image description here][1] the following error
    return query;
}

控制器

public ViewResult ShowDiplomas()
{
    var userName = User.FindFirstValue(ClaimTypes.Name);            
    var diploma = _diplomaRepository.GetAllDiplomasForTeachers(userName);                                    
    if (diploma == null)
    {
        ViewBag.ErrorMessage = $"No diploma is created yet";                
    }
    return View(diploma);
}

数据库表

Teachers
TeacherId,Name,DiplomaId

Diplomas
Id,Title,Description,StudentName,Status,FilePath

Answer 1

您尝试创建的查询要简单得多。通常，如果您具有正确定义的导航属性，则不需要创建加入。

public IEnumerable<Diploma> GetAllDiplomasForTeachers(string username)
{
    var query = context.Diplomas
        .Include(d => d.Teachers)
        .Where(d => d.Teachers.Any(t => t.Name == userName));
    return query;
}