Question

Ok, I must be working too hard because I can’t get my head around what it takes to use the Entity Framework correctly.

Here is what I am trying to do:

I have two tables: HeaderTable and DetailTable. The DetailTable will have 1 to Many records for each row in HeaderTable. In my EDM I set up a Relationship between these two tables to reflect this.

Since there is now a relationship setup between these tables, I thought that by quering all the records in HeaderTable, I would be able to access the DetailTable collection created by the EDM (I can see the property when quering, but it’s null).

Here is my query (this is a Silverlight app, so I am using the DomainContext on the client):

 // myContext is instatiated with class scope
  EntityQuery<Project> query = _myContext.GetHeadersQuery();


  _myContext.Load<Project>(query);   

Since these calls are asynchronous, I check the values after the callback has completed. When checking the value of _myContext.HeaderTable I have all the rows expected. However, the DetailsTable property within _myContext.HeaderTable is empty.

foreach (var h in _myContext.HeaderTable)  // Has records
    {
      foreach (var d in h.DetailTable)  // No records
      {
        string test = d.Description;
      }

I’m assuming my query to return all HeaderTable objects needs to be modified to somehow return all the HeaderDetail collectoins for each HeaderTable row. I just don’t understand how this non-logical modeling stuff works yet.

What am I doing wrong? Any help is greatly appriciated. If you need more information, just let me know. I will be happy to provide anything you need.

Thanks,

-Scott

Answer 1

What you’re probably missing is the Include(), which I think is out of scope of the code you provided.

Check out this cool video; it explained everything about EDM and Linq-to-Entities to me:
http://msdn.microsoft.com/en-us/data/ff628210.aspx

In case you can’t view video now, check out this piece of code I have based on those videos (sorry it’s not in Silverlight, but it’s the same basic idea, I hope).

The retrieval:

public List<Story> GetAllStories()
{
    return context.Stories.Include("User").Include("StoryComments").Where(s => s.HostID == CurrentHost.ID).ToList();
}

Loading the the data:

private void LoadAllStories()
{
    lvwStories.DataSource = TEContext.GetAllStories();
    lvwStories.DataBind();
}

Using the data:

protected void lvwStories_ItemDataBound(object sender, ListViewItemEventArgs e)
{
    if (e.Item.ItemType == ListViewItemType.DataItem)
    {
        Story story = e.Item.DataItem as Story;

        //  blah blah blah....

        hlStory.Text = story.Title;
        hlStory.NavigateUrl = "StoryView.aspx?id=" + story.ID;
        lblStoryCommentCount.Text = "(" + story.StoryComments.Count.ToString() + " comment" + (story.StoryComments.Count > 1 ? "s" : "") + ")";
        lblStoryBody.Text = story.Body;
        lblStoryUser.Text = story.User.Username;
        lblStoryDTS.Text = story.AddedDTS.ToShortTimeString();
    }            
}