DB Context - Query to select post from a category - asp.net-mvc

Question

I am using DB context approach in my asp.net mvc 4 test project.
Here are my domain classes
Category.cs
public class Categroy
{
public virtual int Id { get; set; }
public virtual string CategoryName{ get; set; }
public virtual ICollection<Post> Post{ get; set; }
}
Post.cs
public class Post
{
public virtual int Id { get; set; }
public virtual string Title { get; set; }
public virtual string Description { get; set; }
}
IPostsDateSource.cs
public interface IPostsDataSource
{
IQueryable<Category> Categories{ get; }
IQueryable<Post> Posts { get; }
void Save();
}
PostsDB.cs
public class PostsDB:DbContext,IPostsDataSource
{
public PostsDB():base("DefaultConnection")
{
}
public DbSet<Category> Categories{ get; set; }
public DbSet<Post> Posts{ get; set; }
void IPostsDataSource.Save()
{
SaveChanges();
}
IQueryable<Category> IPostsDataSource.Categories
{
get { return Categories; }
}
IQueryable<Post> IPostsDataSource.Posts
{
get { return Posts; }
}
}
I am using StructureMap for mapping
IoC.cs
...
x.For<IPostsDataSource>().HttpContextScoped().Use<PostsDB>();
...
In my HomeController I am
private IPostDataSource _db;
public HomeController(IAdsDataSource db)
{
_db = db;
}
I can retrieve all the posts by _db.Posts
public ActionResult Index()
{
var Posts= _db.Posts;
ViewBag.Posts = Posts;
return View();
}
The problem is what query should I write in order to retrieve all posts from a specific categrory

Answer 1

If a category has a collection of Posts, then Post entity should have a CategoryID property. You can query base on that CategoryID.
Otherwise you can query the category and retrieve the corresponding list of Posts:
var cat = _db.Categories.Where(a => a.Id == catId).FirstOrDefault();
if(cat != null)
ViewBag.Posts = cat.Posts;
return View();