1 class MyContext : DbContext
 2 {
 3     public DbSet<Post> Posts { get; set; }
 4     public DbSet<Tag> Tags { get; set; }
 5 
 6     protected override void OnModelCreating(ModelBuilder modelBuilder)
 7     {
 8         modelBuilder.Entity<PostTag>()
 9             .HasKey(t => new { t.PostId, t.TagId });
10 
11         modelBuilder.Entity<PostTag>()
12             .HasOne(pt => pt.Post)
13             .WithMany(p => p.PostTags)
14             .HasForeignKey(pt => pt.PostId);
15 
16         modelBuilder.Entity<PostTag>()
17             .HasOne(pt => pt.Tag)
18             .WithMany(t => t.PostTags)
19             .HasForeignKey(pt => pt.TagId);
20     }
21 }
22 
23 public class Post
24 {
25     public int PostId { get; set; }
26     public string Title { get; set; }
27     public string Content { get; set; }
28 
29     public List<PostTag> PostTags { get; set; }
30 }
31 
32 public class Tag
33 {
34     public string TagId { get; set; }
35 
36     public List<PostTag> PostTags { get; set; }
37 }
38 
39 public class PostTag
40 {
41     public int PostId { get; set; }
42     public Post Post { get; set; }
43 
44     public string TagId { get; set; }
45     public Tag Tag { get; set; }
46 }