Question

我正在为练习构建一个简单的API，如下所示：

我的学生，入学和课程模型是这样的：

 public class Student
    {
        public int ID { get; set; }
        public string LastName { get; set; }
        public string FirstMidName { get; set; }
        public DateTime EnrollmentDate { get; set; }

        public ICollection<Enrollment> Enrollments { get; set; }
    }

namespace.Models.School
{
public enum Grade
{
    A, B, C, D, F
}
public class Enrollment
{
    public int EnrollmentID { get; set; }
    public int CourseID { get; set; }
    public int StudentID { get; set; }
    public Grade? Grade { get; set; }

    public Course Course { get; set; }
    public Student Student { get; set; }
 }
}

 public class Course
{
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    public int CourseID { get; set; }
    public string Title { get; set; }
    public int Credits { get; set; }

    public ICollection<Enrollment> Enrollments { get; set; }
}

我的DbContext是这样的：

    public DbSet<Course> Courses { get; set; }
    public DbSet<Enrollment> Enrollments { get; set; }
    public DbSet<Student> Students { get; set; }

我的控制器中有两种方法，如下所示：

    [HttpGet]
    public async Task<IEnumerable<Student>> GetAllSudents()
    {

        var students = await _context.Students.ToListAsync();
        return (students);

    }

   [HttpGet("{id}")]
    public async Task<IActionResult> GetSingleStudent(int id)
    { 

    return Ok( await _context.Students
                   .Include(s => s.Enrollments)
                    .ThenInclude(e => e.Course)
                       .FirstOrDefaultAsync(m => m.ID == id));
     }

现在，GetAllStudets（）函数正常运行，Chrome和邮差中的所有学生，GetSingleStudent（）也会在Chrome中连续加载并在控制台中出现此错误时带回单个学生结果：

36:1 GET http://localhost:49170/api/students/36 net::ERR_CONNECTION_RESET

在Postman中，它只是说：

Could not get any response 
There was an error connecting to http://localhost:49170/api/students/36

我的问题是，如何摆脱这个错误并改进这个Api？

Answer 1

我发现我的学生表有一个注册集合，在内部注册我有课程，在课程内我再次注册。所以它导致了自我引用循环。为了解决这个问题，我必须在域模型之上创建Resources类，这样我的StudentResource看起来就像我的域模型一样：

public class StudentResource
{
    public int ID { get; set; }
    public string LastName { get; set; }
    public string FirstMidName { get; set; }
    public DateTime EnrollmentDate { get; set; }

    public ICollection<EnrollmentResource> Enrollments { get; set; }
}

但我必须更改EnrollmentResource类，该类不应该包含对学生和课程的反向引用。

public class EnrollmentResource
{
    public int EnrollmentID { get; set; }
    public int CourseID { get; set; }

    public Grade? Grade { get; set; }

}

在我的MappingProfile.cs类中，我将它们映射为：

        CreateMap<Student, StudentResource>();
        CreateMap<Enrollment, EnrollmentResource>();

最后我不得不改变GetSingleStudent（int id）方法类型的返回，如下所示：

  return Ok(_mapper.Map<Student, StudentResource>(singleStudent));

错误不正确。

Microsoft Entity Framework ASP NETCore API相关数据

1 个答案: