实体框架核心2.2.6多对多关系(表创建时的额外列)

// 定义实体类
public class Student
{
    public int StudentId { get; set; }
    public string Name { get; set; }
    public ICollection<Course> Courses { get; set; }
}

public class Course
{
    public int CourseId { get; set; }
    public string Title { get; set; }
    public ICollection<Student> Students { get; set; }
    public ICollection<Enrollment> Enrollments { get; set; }
}

public class Enrollment
{
    public int EnrollmentId { get; set; }
    public int StudentId { get; set; }
    public int CourseId { get; set; }
    public DateTime EnrollmentDate { get; set; }
    public Grade Grade { get; set; }
    public Student Student { get; set; }
    public Course Course { get; set; }
}

// 配置多对多关系
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Enrollment>()
        .HasKey(e => new { e.StudentId, e.CourseId });

    modelBuilder.Entity<Enrollment>()
        .HasOne(e => e.Student)
        .WithMany(s => s.Enrollments)
        .HasForeignKey(e => e.StudentId);

    modelBuilder.Entity<Enrollment>()
        .HasOne(e => e.Course)
        .WithMany(c => c.Enrollments)
        .HasForeignKey(e => e.CourseId);
}