EF add data to the same navigation property many to many .

Question

I have a post table and a tag table and bridge table PostTag.

 

Post 1 has 23 tags , meaning

  post p= context.posts.where(p=>p.id=12);

 p.tags.Count() =12;

 

Ok ,fine.

Now I added some new tags to tag table but i want to attach these tags to the same old post

 

so what i did,

Post p= context.posts.where(p=.p.id=12);
foreach(tag t in tags)
{
p.tags.add(t);
}
context.savechanges();

 

There is no error, but no output aswell , meaning still post has old tags and new tags are not added to the post.