EF Core 多对多简单配置

1、创建实体类
Student

internal class Student
{
    public long Id { get; set; }
    public string StuName { get; set; }
    public List<Teacher> Teachers { get; set; } = new List<Teacher>();
}

Teacher

internal class Teacher
{
    public long Id { get; set; }
    public string TeaName { get; set; }
    public List<Student> Students { get; set; } = new List<Student>();
}

2、创建配置文件，配置多对多关系，并指定中间表表名
StudentConfig

internal class StudentConfig : IEntityTypeConfiguration<Student>
{
    public void Configure(EntityTypeBuilder<Student> builder)
    {
        builder.ToTable("T_Students");
        builder.HasMany<Teacher>(s => s.Teachers).WithMany(t=> t.Students)
            .UsingEntity(u => u.ToTable("T_Students_Related_Teachers"));
    }
}

TeacherConfig

internal class TeacherConfig : IEntityTypeConfiguration<Teacher>
{
    public void Configure(EntityTypeBuilder<Teacher> builder)
    {
        builder.ToTable("T_Teachers");
    }
}

3、创建MyDbContext

 class MyDbContext:DbContext
{
    public DbSet<Student> Students { get; set; }
    public DbSet<Teacher> Teachers { get; set; }
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        base.OnConfiguring(optionsBuilder);
        optionsBuilder.UseSqlServer("Server=DESKTOP-7K7ADF7;Database=EFCore5;User Id=sa;Password=XXXXTrustServerCertificate=True;Trusted_Connection=True;MultipleActiveResultSets=True;");
        //    .EnableSensitiveDataLogging() // 显示敏感数据（仅用于调试）
        //    .LogTo(Console.WriteLine, LogLevel.Debug);
    }
    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);
        modelBuilder.ApplyConfigurationsFromAssembly(this.GetType().Assembly);       
    }
}

4、生成迁入脚本，并更新到数据库生成表结构

Add-Migration AddStuAndTeacher

update-database

5、插入数据、查询数据

using (MyDbContext dbContext = new MyDbContext())
{
    //Student student1 = new Student() { StuName="张三"};
     //Student student2 = new Student() { StuName = "李四" };
     //Student student3 = new Student() { StuName = "王五" };

     //Teacher teacher1 = new Teacher() { TeaName= "Mr Lei" };
     //Teacher teacher2 = new Teacher() { TeaName = "Mr Chen" };
     //Teacher teacher3 = new Teacher() { TeaName = "Mr Zhou" };

     //student1.Teachers.Add(teacher1);
     //student1.Teachers.Add(teacher2);

     //student2.Teachers.Add(teacher2);
     //student2.Teachers.Add(teacher3);

     //student3.Teachers.Add(teacher1);
     //student3.Teachers.Add(teacher2);
     //student3.Teachers.Add(teacher3);

     //dbContext.Students.Add(student1);
     //dbContext.Students.Add(student2);
     //dbContext.Students.Add(student3);

     //dbContext.Teachers.Add(teacher1);
     //dbContext.Teachers.Add(teacher2);
     //dbContext.Teachers.Add(teacher3);

     //await dbContext.SaveChangesAsync();
     //通过学生査老师
     var students = dbContext.Students.Include(s => s.Teachers);
     foreach (var student in students)
     {
         Console.WriteLine($"{student.StuName}的老师如下：");
         foreach (var teacher in student.Teachers)
         {
             Console.WriteLine(teacher.TeaName);
         }
     }
     //通过老师查学生
     var teachers = dbContext.Teachers.Include(s => s.Students);
     foreach (var teacher in teachers)
     {
         Console.WriteLine($"{teacher.TeaName}的学生如下：");
         foreach (var student in teacher.Students)
         {
             Console.WriteLine(student.StuName);
         }
     }
}