包括第3层相关的集合，并使用代码优先实体框架在gridview中显示

Question

I have the following template fields in my gridview (ItemType attribute is set properly: ItemType="gEchoLu.Model.DiscussionTimeframe" ):

        <asp:TemplateField HeaderText="Discussion Wall">
            <ItemTemplate>
                <asp:Label runat="server" ID="lbl_Discussion" Text="<%#Item.DiscussionWall.WallTitle %>"></asp:Label>
            </ItemTemplate>
        </asp:TemplateField>

        <asp:TemplateField HeaderText="Course">
            <ItemTemplate>
                <asp:Label runat="server" ID="lbl_Discussion" Text="<%#Item.DiscussionWall.Course.CourseTitle %>"></asp:Label>
            </ItemTemplate>
        </asp:TemplateField>

The first field is displayed correctly. However, the second template field is always null. Here is the code by which I bind data to the gridview:

        gEchoLuDBContext db = new gEchoLuDBContext();
        var timeframes = db.Timeframes.Include(c => c.DiscussionWall.Course).Where(tf => tf.CreatedBy == userid).ToList();

        grd_Timeframes.DataSource = timeframes;
        grd_Timeframes.DataBind();

When I debug it, the properties of Course is null actually. In my model, each TimeFrame belongs to a DiscussionWall , and each DiscussionWall belongs to a Course . However, there is no direct relationship between a TimeFrame and a Course . I am not sure if what I want is doable in this situation. Do I have to define a (1-to-many) relationship between TimeFrame an DiscussionWall entities to achieve what I want? (I know this can be done by using OnDataBound , but I wonder if ItemType can be used to handle this quickly).

Here are the related parts of my model:

public class DiscussionWall
{
    [Key]
    public int WallId { get; set; }

    [Required]
    [StringLength(200)]
    public string WallTitle { get; set; }

    [Required]
    [ForeignKey("Course")]
    public int CourseId { get; set; }

    private Course _course;
    public Course Course
    {
        get { return _course?? (_course = new Course());}
        set { _course = value; }
    }

    public List<DiscussionTimeframe> Timeframes { get; set; }
}

public class DiscussionTimeframe
{
    public int DiscussionTimeframeId { get; set; }

    [Required]
    public string TimeFrameName { get; set; }

    public int DiscussionWallId { get; set; }

    [ForeignKey("DiscussionWallId")]
    public DiscussionWall DiscussionWall { get; set; }
}

public class Course
{
    public int CourseId { get; set; }

    public string CourseTitle { get; set; }

    public List<DiscussionWall> DiscussionWalls { get; set; }
}

Answer 1

It worked when I change this:

private Course _course;
public Course Course
{
    get { return _course?? (_course = new Course());}
    set { _course = value; }
}

into this:

public Course Course
{
    get;
    set;
}