How do I chain properties with Code First entity framework? - entity-framework

Question

I'm trying to do what seems fairly simple but I'm getting a null reference....
I have a null on the assoc files property in the last statement...
TestInfo.AggregateRoutes.MainBlogEntry = new Blog { BlogType = 1, Title = TestInfo.UniqueRecordIdentifier, Description = TestInfo.UniqueRecordIdentifier, DateAdded = DateTime.Now, User = TestInfo.UniqueRecordIdentifier };
IBlogRepository blogRepo = new BlogRepository();
var assocFile = new AssocFile { Name = TestInfo.UniqueRecordIdentifier, Url = TestInfo.UniqueRecordIdentifier };
TestInfo.AggregateRoutes.MainBlogEntry.AssocFiles.Add(assocFile);
This is the code I have written to support what I'm trying to do...
public class PteDotNetContext : DbContext
{
public DbSet<Blog> Blogs { get; set; }
public DbSet<AssocFile> AssocFiles { get; set; }
}
public class Blog
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int BlogId { get; set; }
public int BlogType { get; set; }
public string Title { get; set; }
public string Description { get; set; }
public DateTime DateAdded { get; set; }
public string User { get; set; }
public virtual ICollection<AssocFile> AssocFiles { get; set; }
}
public class AssocFile
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int AssocFileId { get; set; }
public int BlogId { get; set; }
public string Url { get; set; }
public string Name { get; set; }
public virtual Category Category { get; set; }
}
I thought the whole point in declaring it virtual was that it would create a foreign key constraint?

Answer 1

When you instantiate an entity you also need to initialize the collection navigational properties before you access it for the first time. In your case MainBlogEntry.AssocFiles = new List<AssocFile>();. The reason for this is, your property implementation does not contain any logic to initialize the collection.
When EF creates new instances of your entities, it sub classes your entities (ie Proxy Creation) and over ride the default functionality of your properies.
TestInfo.AggregateRoutes.MainBlogEntry = new Blog { BlogType = 1, Title = TestInfo.UniqueRecordIdentifier, Description = TestInfo.UniqueRecordIdentifier, DateAdded = DateTime.Now, User = TestInfo.UniqueRecordIdentifier };
IBlogRepository blogRepo = new BlogRepository();
var assocFile = new AssocFile { Name = TestInfo.UniqueRecordIdentifier, Url = TestInfo.UniqueRecordIdentifier };
TestInfo.AggregateRoutes.MainBlogEntry.AssocFiles = new List<AssocFile>();
TestInfo.AggregateRoutes.MainBlogEntry.AssocFiles.Add(assocFile);