EF-code-first多对多相关对象生成两个不同的SQL表(MVC3)

Question

我读过this great Q&A，我试着做一些类似的东西。我的模型类包括：

public class Person
{
    public int PersonId { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }

    public ICollection<Course> CoursesAttending { get; set; }

    public Person()
    {
        this.CoursesAttending = new List<Course>();
    }
}

public class Course
{
    public int CourseId { get; set; }
    public string Title { get; set; }

    public ICollection<Person> Students { get; set; }
}

public class PersonCourse
{
    [Key, Column(Order = 0)]
    public int PersonID { get; set; }
    [Key, Column(Order = 1)]
    public int CourseID { get; set; }

    public virtual Person Student { get; set; }
    public virtual Course StudentCourse { get; set; }

    public int Mark { get; set; }
    public string Comment { get; set; }
}

public class SchoolContext : DbContext
{
    public DbSet<Course> Courses { get; set; }
    public DbSet<Person> People { get; set; }
    public DbSet<PersonCourse> PersonCourseLinks { get; set; }

    public SchoolContext()
        : base("ManyToManyTest")
    {
    }
}

现在，我尝试添加一个新人，并将新课程添加到他的课程列表中：

[HttpPost]
    public ActionResult Create(Person person)
    {
        if (ModelState.IsValid)
        {
            Course studentCourse;
            try
            {
                studentCourse = db.Courses.ToList<Course>().First();
            }
            catch
            {
                studentCourse = new Course() { Title = "HTML" };
            }

            person.CoursesAttending.Add(studentCourse);
            db.People.Add(person);
            db.SaveChanges();
            return RedirectToAction("Index");  
        }

        return View(person);
    }

一切正常，但是当我打开我创建的数据库时，我看到Person和Course类有两个链接表-PersonCourses(带有字段: PersonID，CourseID，Mark，Comment)和PersonCourse1 (带有字段: PersonID，CourseID)，并且只有PersonCourse1有行(实际上是一行)。为什么会发生这种情况？我做错什么了吗？我希望只看到一个链接表-- PersonCourses表...

Answer 1

我希望只看到一个链接表- PersonCourses表

然后，您必须通过CoursesAttending导航属性将PersonCourse实体与Person实体链接起来。对Course实体也要做同样的事情。

public class Person
{
    public int PersonId { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }

    public ICollection<PersonCourse> CoursesAttending { get; set; }

    public Person()
    {
        this.CoursesAttending = new List<PersonCourse>();
    }
}

public class Course
{
    public int CourseId { get; set; }
    public string Title { get; set; }

    public ICollection<PersonCourse> Students { get; set; }
}

Answer 2

为gerund表中的外键属性提供外键关联：

public class PersonCourse
{
    [Key, Column(Order = 0)]
    public int PersonID { get; set; }
    [Key, Column(Order = 1)]
    public int CourseID { get; set; }

    [ForeignKey("PersonID")]
    public virtual Person Student { get; set; }

    [ForeignKey("CourseID")]
    public virtual Course StudentCourse { get; set; }

    public int Mark { get; set; }
    public string Comment { get; set; }
}

Answer 3

现在你可以知道为什么你的代码没有像预期的那样工作：

public class PersonCourse
{
    [Key, Column(Order = 0)]
    public int PersonID { get; set; }
    [Key, Column(Order = 1)]
    public int CourseID { get; set; }

    public virtual Person Person { get; set; } // Follow built in conventions
    public virtual Course Course { get; set; }

    public int Mark { get; set; }
    public string Comment { get; set; }
}

这现在遵循了内置的实体框架约定

public int [ClassName][Id] or [Id] //Database Foreign Key column

and

public NavigationProperty [ClassName] // Navigation Property