具有多对多关系的类上的CRUD操作示例|实体框架核心

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 class SchoolContext : DbContext
{
    public DbSet<Student> Students { get; set; }
    public DbSet<Course> Courses { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Student>()
            .HasMany(s => s.Courses)
            .WithMany(c => c.Students)
            .UsingEntity(j => j.ToTable("StudentCourse"));
    }
}

using (var context = new SchoolContext())
{
    // 创建学生和课程
    var student1 = new Student { Name = "Alice" };
    var student2 = new Student { Name = "Bob" };
    var course1 = new Course { Title = "Math" };
    var course2 = new Course { Title = "English" };

    // 关联学生和课程
    student1.Courses.Add(course1);
    student1.Courses.Add(course2);
    student2.Courses.Add(course1);

    // 添加到数据库
    context.Students.Add(student1);
    context.Students.Add(student2);
    context.SaveChanges();

    // 查询学生所选的课程
    var selectedCourses = context.Students
        .Include(s => s.Courses)
        .FirstOrDefault(s => s.Name == "Alice")
        .Courses;

    // 更新学生所选的课程
    var student = context.Students
        .Include(s => s.Courses)
        .FirstOrDefault(s => s.Name == "Alice");
    var course = context.Courses.FirstOrDefault(c => c.Title == "Math");
    student.Courses.Remove(course);
    context.SaveChanges();

    // 删除学生和课程
    var studentToDelete = context.Students.FirstOrDefault(s => s.Name == "Bob");
    context.Students.Remove(studentToDelete);
    context.SaveChanges();
}