inserting data in database table in one to many relationship in code first - asp.net-mvc-4

Question

I am using Code First Approach with Mvc4.For authentication and authorization, simple membership is being used.
My UserProfile class have these fields where a user can have multiple posts and comments.
[Table("UserProfile")]
public class UserProfile
{
public UserProfile()
{
this.PostComments = new HashSet<PostComment>();
this.Posts = new HashSet<Post>();
}
[Key]
[DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
public int UserId { get; set; }
public string UserName { get; set; }
public string AvatarExt { get; set; }
public virtual ICollection<PostComment> PostComments { get; set; }
public virtual ICollection<Post> Posts { get; set; }
}
and my Post class is something like this.here i have configured one to many relationship between userprofile class and Post class.
public class Post
{
public Post()
{
this.PostComments = new HashSet<PostComment>();
}
[Key]
public int PostId { get; set; }
public string Message { get; set; }
public int PostedBy { get; set; }
public System.DateTime PostedDate { get; set; }
public virtual ICollection<PostComment> PostComments { get; set; }
public virtual UserProfile UserProfile { get; set; }
}
and this is my controller's action method for adding posts to the post table in the database.
public HttpResponseMessage PostPost(Post post)
{
post.PostedBy = WebSecurity.CurrentUserId;
post.PostedDate = DateTime.UtcNow;
// post.UserProfile.UserId = WebSecurity.CurrentUserId;
ModelState.Remove("post.PostedBy");
ModelState.Remove("post.PostedDate");
// ModelState.Remove("post.UserProfile.UserId");
if (ModelState.IsValid)
{
db.Posts.Add(post);
db.SaveChanges();
var usr = db.UserProfiles.FirstOrDefault(x => x.UserId == post.PostedBy);
var ret = new
{
Message = post.Message,
PostedBy = post.PostedBy,
PostedByName = usr.UserName,
PostedByAvatar = imgFolder + (String.IsNullOrEmpty(usr.AvatarExt) ? defaultAvatar : post.PostedBy + "." + post.UserProfile.AvatarExt),
PostedDate = post.PostedDate,
PostId = post.PostId
};
HttpResponseMessage response = Request.CreateResponse(HttpStatusCode.Created, ret);
response.Headers.Location = new Uri(Url.Link("DefaultApi", new { id = post.PostId }));
return response;
}
else
{
return Request.CreateErrorResponse(HttpStatusCode.BadRequest, ModelState);
}
}
when i tried to debug this action method, i found out that it is passing null at this line---
PostedByName = usr.UserName
what should i do to pass current loggedIn userName to the database.
One more information i want to share is--
In Sql Server, it is creating 5 columns----
PostId(which is primary key),
Message,PostedBy(int),PostedDate, UserProfile_UserId(Foreign key column).
Now, everything is working fine but in UserProfile_UserId column, it is storing null.
I know it should not be null but how.
What i am missing.what should i do.There was slight change in this code using dbFirst approach, and that code is working fine.
To get post on the view page, action method is----
public dynamic GetPosts()
{
var ret = (from post in db.Posts.ToList()
orderby post.PostedDate descending
select new
{
Message = post.Message,
PostedBy = post.PostedBy,
PostedByName = post.UserProfile.UserName,
PostedByAvatar = imgFolder + (String.IsNullOrEmpty(post.UserProfile.AvatarExt) ? defaultAvatar : post.PostedBy + "." + post.UserProfile.AvatarExt),
PostedDate = post.PostedDate,
PostId = post.PostId,
PostComments = from comment in post.PostComments.ToList()
orderby comment.CommentedDate
select new
{
CommentedBy = comment.CommentedBy,
CommentedByName = comment.UserProfile.UserName,
CommentedByAvatar = imgFolder + (String.IsNullOrEmpty(comment.UserProfile.AvatarExt) ? defaultAvatar : comment.CommentedBy + "." + comment.UserProfile.AvatarExt),
CommentedDate = comment.CommentedDate,
CommentId = comment.CommentId,
Message = comment.Message,
PostId = comment.PostId
}
}).AsEnumerable();
return ret;
}
this is the action method where i want to show post and comment with their UserName.here, PostedByName is returning null.