ef core中如何实现多对多的表映射关系

文档：https://docs.microsoft.com/en-us/ef/core/modeling/relationships

 class MyContext : DbContext
  {
      public DbSet<Post> Posts { get; set; }
      public DbSet<Tag> Tags { get; set; }

      protected override void OnModelCreating(ModelBuilder modelBuilder)
      {
          modelBuilder.Entity<PostTag>()
              .HasKey(t => new { t.PostId, t.TagId });

         modelBuilder.Entity<PostTag>()
             .HasOne(pt => pt.Post)
             .WithMany(p => p.PostTags)
             .HasForeignKey(pt => pt.PostId);

         modelBuilder.Entity<PostTag>()
             .HasOne(pt => pt.Tag)
             .WithMany(t => t.PostTags)
             .HasForeignKey(pt => pt.TagId);
     }
 }

 public class Post
 {
     public int PostId { get; set; }
     public string Title { get; set; }
     public string Content { get; set; }

     public List<PostTag> PostTags { get; set; }
 }

 public class Tag
 {
     public string TagId { get; set; }

     public List<PostTag> PostTags { get; set; }
 }

 public class PostTag
 {
     public int PostId { get; set; }
     public Post Post { get; set; }

     public string TagId { get; set; }
     public Tag Tag { get; set; }
 }