Entity Framework relate second table - asp.net-mvc

Question

How can I relate the tables below by fluent api?
I need to get the second table data via LinkTable which stores ids of Main and Second tables.
Here are my models:
public class MainTable
{
public int ID { get; set; }
...
...
public ICollection<LinkTable> LinkTable { get; set; }
}
public class LinkTable
{
public int ID { get; set; }
...
...
public MainTable MainTable { get; set; }
public SecondTable SecondTable { get; set; }
}
public class SecondTable
{
public int ID { get; set; }
...
...
public ICollection<LinkTable> LinkTable { get; set; }
}
I mapped like this:
HasRequired(t => t.MainTable).WithMany(t => t.LinkTable).HasForeignKey(t => t.MainTable_ID);
HasRequired(t => t.SecondTable).WithMany(t => t.LinkTable).HasForeignKey(t => t.SecondTable_ID);
And trying to get data :
MyDBContext.MainTable.Include("LinkTable").FirstOrDefault();
When I was trying foreach the LinkTable to get SecondTable data I got an error:
Object reference not set...
#foreach (var item in Model.LinkTable)
{
<p>#item.SecondTable.ID</p>
}

Answer 1

To avoid that exception, you need to initialize your navigation property in a constructor:
public class MainTable
{
public MainTable()
{
LinkTable=new List<LinkTable>();
}
public int ID { get; set; }
...
...
public ICollection<LinkTable> LinkTable { get; set; }
}
Also, you could use Include extension method which is strongly typed and could avoid you possible run-time exceptions:
MyDBContext.MainTable.Include(mt=>mt.LinkTable).FirstOrDefault();
Now if you want to load another level, in this case SecondTable, you can do this:
MyDBContext.MainTable.Include(mt=>mt.LinkTable.Select(lt=>lt.SecontTable)).FirstOrDefault();
In the link I quoted above you can find more examples about how to load different levels.