entity framework many to many inserts code first - asp.net-mvc

Question

this is my model
public class Post
{
public long PostID { get; set; }
[Required]
[MaxLength(255)]
public string Title { get; set; }
}
public class Tag
{
public long TagID { get; set; }
[Required]
[Display(Name = "Tag Name")]
[MaxLength(30)]
public string TagName { get; set; }
public bool IsActive { get; set; }
}
public class TagPost
{
public long TagPostID { get; set; }
public long PostID { get; set; }
public long TagID { get; set; }
[ForeignKey("PostID")]
public virtual Post Posts { get; set; }
[ForeignKey("TagID")]
public virtual Tag Tags { get; set; }
}
1) Is this the right many to many configuration in EF 4.1 without mentioning the modelbinder for many to many.
2) if i have completed the many to many configuration using dataannotation why the data is not inserting in tagpost .
public void InsertPostQuestion(Post post,List<string> tags)
{
context.Posts.Add(post);
foreach (string tag in tags)
{
Tag tagr = new Tag();
tagr.TagName = tag;
tagr.IsActive = true;
context.Tags.Add(tagr);
}
context.SaveChanges();
}
3) I do have to define modelbinder to have many to many inserts or delete or update?
modelBuilder.Entity<Post>().
HasMany(c => c.Tags).
WithMany(p => p.Posts).
Map(
m =>
{
m.MapLeftKey("PostID");
m.MapRightKey("TagID");
m.ToTable("TagPost");
});

Answer 1

Change your models to this:
public class Post
{
public long PostID { get; set; }
[Required]
[MaxLength(255)]
public string Title { get; set; }
public bool IsActive { get; set; }
public virtual List<Tag> Tags { get; set; }
}
public class Tag
{
public long TagID { get; set; }
[Required]
[Display(Name = "Tag Name")]
[MaxLength(30)]
public string TagName { get; set; }
public bool IsActive { get; set; }
public virtual List<Post> Posts { get; set; }
}
and then save like so:
public void InsertPostQuestion(Post post,List<string> tags)
{
context.Posts.Add(post);
foreach (string tag in tags)
{
// TODO: If tag has a unique index on TagName, see if it exists first
Tag tagr = new Tag();
tagr.TagName = tag;
tagr.IsActive = true;
context.Tags.Add(tagr);
post.Tags.Add(tagr);
}
context.SaveChanges();
}
EF will create the intermediate table in the db and populate it nicely automatically.