使用.NET EF Core 5 TrackableEntities更新多对多集合

// 创建多对多关系的实体类
public class Student
{
    public int Id { get; set; }
    public string Name { get; set; }
    public ICollection<Course> Courses { get; set; } = new List<Course>();
}

public class Course
{
    public int Id { get; set; }
    public string Name { get; set; }
    public ICollection<Student> Students { get; set; } = new List<Student>();
}

// 定义模型关系
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Student>()
        .HasMany(s => s.Courses)
        .WithMany(c => c.Students)
        .UsingEntity<Dictionary<string, object>>(
            "StudentCourse",
            j => j
                .HasOne<Course>()
                .WithMany()
                .HasForeignKey("CourseId"),
            j => j
                .HasOne<Student>()
                .WithMany()
                .HasForeignKey("StudentId"),
            j =>
            {
                j.Property<int>("Id").HasValueGenerator<InMemoryIntegerValueGenerator<int>>();
                j.HasKey("Id");
                j.ToTable("StudentCourses");
            });
}

// 更新多对多集合
using (var dbContext = new YourDbContext())
{
    var student = dbContext.Students
        .Include(s => s.Courses)
        .FirstOrDefault(s => s.Id == studentId);

    if (student != null)
    {
        // 使用ChangeTrackingCollection来跟踪集合的更改
        var coursesCollection = new ChangeTrackingCollection<Course>(student.Courses);

        // 添加新的课程
        var newCourse = new Course { Name = "New Course" };
        coursesCollection.Add(newCourse);

        // 删除已有的课程
        var courseToRemove = student.Courses.FirstOrDefault(c => c.Name == "Course to Remove");
        if (courseToRemove != null)
        {
            coursesCollection.Remove(courseToRemove);
        }

        // 更新集合中的课程
        var courseToUpdate = student.Courses.FirstOrDefault(c => c.Name == "Course to Update");
        if (courseToUpdate != null)
        {
            courseToUpdate.Name = "Updated Course";
            coursesCollection.Update(courseToUpdate);
        }

        // 保存更改
        dbContext.SaveChanges();
    }
}