实体框架5多对多

Question

我有问题，因为当我将以下代码添加到Course类中时，我只有2个表，而不是3个表

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

你没有把这三行都写好，但我需要在课程中增加一个字段

public class Person
{
    public int PersonId { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public virtual ICollection<Course> CoursesAttending { get; set; }
}

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

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

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

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

class Program
{
    static void Main(string[] args)
    {
        Database.SetInitializer<SchoolContext>(
                new DropCreateDatabaseAlways<SchoolContext>());

        SchoolContext db = new SchoolContext();
        var cos = from d in db.Courses
                  select d;
    }
}

请帮帮我

Answer 1

EF无法确定是Course.Student还是Course.Students引用Person.CoursesAttending。您必须给EF一个提示，例如通过在Course.Students上使用[InverseProperty]属性

[InverseProperty("CoursesAttending")]
public virtual ICollection<Person> Students { get; set; }

编辑

该模型将导致多个级联删除路径，即:当您删除一个Person时，join表中的记录也将被删除，但它还将删除此人通过Course.Person属性分配到的所有Course。删除的Course%s将再次删除连接表中的记录，这是同一表上的第二个删除路径。

SQL Server不支持多条级联删除路径，必须通过Fluent API禁用：

public class MyContext : DbContext
{
    //...

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Course>()
            .HasRequired(c => c.Student)
            .WithMany()
            .HasForeignKey(c => c.PersonId)
            .WillCascadeOnDelete(false);
    }
}