TITLE!

So, yesterday I actually started working with the Entity framework with a tad more complex queries than the basic select of a single Entity. The first issue I ran into is the flattening of a single Entity 1* Entity relationship. By default the Entity framework and the EntityDataSource actually keeps something similar to an DataTable->ChildDataTable relationship with a prebuilt relationship. Unfortunately the ability to flatten this data is not inherently built in, and join syntax needs to be used:

SELECT E.ID, E.Field, r.Field2 from EntitySet AS E INNER JOIN Entity2Set AS r ON r.Entity = E

Which creates our flattened list of Entities for us based on the defined relationship.

Secondly: EntityDataSource and 1-1 relationships/child objects/picklists. This is much easier to do via the Entity framework and is simply defined via the “Include” parameter.

Ex:

   <asp:EntityDataSource ID="x_EntityDataSource" runat="server"
      ConnectionString="name=DataEntities"
      DefaultContainerName="DataEntities" Where="it.ID = @EntityID"
      EntitySetName="EntitySet" EnableUpdate="True" Include="SubEntity">
      <WhereParameters>
         <asp:QueryStringParameter Name="EntityId" QueryStringField="ID" Type="Int32" />
      </WhereParameters>
   </asp:EntityDataSource>

Which provides us with the Entity, and a secondary child Entity which is an FK relationship to a single value.
And, lastly some great posts from the Microsoft team:
http://blogs.msdn.com/diego/archive/2008/05/13/entitydatasource-to-wrap-or-not-to-wrap.aspx
http://blogs.msdn.com/diego/archive/2008/05/24/entitydatasource-s-flattening-of-complex-type-properties.aspx

http://blogs.msdn.com/zlatkom/archive/2007/07/10/entity-sql.aspx