Can't Get EF4 Eager Loading of Subclassed Entities to Work

Question

I have an abstract Content entity in my EF4 model with a concrete subclass, MultipleChoiceItem. There is a related table in the case of MultipleChoiceItem accessed by a Navigation property on the MultipleChoiceItem entity called Options. I would like to eager-load the Options result because if you're getting a MultipleChoiceItem, you always want the Options. However, I can't seem to get this to work. Here is what I've bascially done:

• The MultipleChoiceItem is a subclass, therefore it didn't get metadata created by default. So, I created a metadata class for it that looks sort of like this:

  [MetadataTypeAttribute(typeof(MultipleChoiceItem.ContentMetadata))]
  public partial class MultipleChoiceItem
  {
      internal sealed class MultipleChoiceItemMetadata
      {
          ... other stuff ... 
          [Include]  
          public EntityCollection<McOption> Options { get; set; }
          ... other stuff ...
      }
  

• I then created a new query in the ContentService that looks like this:

  public IQueryable<Content> GetMultipleChoiceItems()  
  {  
      return this.ObjectContext.Contents.OfType<MultipleChoiceItem>()
          .Include("Options");  
  }
  

In a unit test, I'm calling that like this:

    context = new ContentContext();
    var loadOperation = context.Load(context.GetMultipleChoiceItemsQuery());
    loadOperation.Completed += new EventHandler(CompletedHandler);

Once I get into the CompletedHandler, the following code doesn't seem to have the Options property loaded--in fact, Options.Count == 0 when it should be 4 (verified by checking the underlying data store).

    MultipleChoiceItem mci = context.Contents.First(c => c.ContentId == mciId) as MultipleChoiceItem;

Can anyone tell me what I'm doing wrong? I've tried to follow the models I've seen posted and am apparently missing something...

Thanks!

Answer 1

My metadata type attribute for the metadata that I had to do by hand (since RIA doesn't make metadata for subclasses by default for some reason) had the wrong type. It inadvertantly read:

[MetadataTypeAttribute(typeof(MultipleChoiceItem.ContentMetadata))]

And should have read:

[MetadataTypeAttribute(typeof(MultipleChoiceItem.MultipleChoiceMetadata))] 

The fact that there is no metadata generated for subclasses is quite annoying.

Anyhow, posting here in case anyone else has this issue!