实体框架ArgumentNullException

Question

I have database with simple structure:

markimaster(id, name), modelemaster(id, marka_id), typymaster(id, model_id)

I defined relationships between tables and fetch data with this code:

ObjectQuery<markimaster> markiQuery = context.markimaster.Include("modelemaster.typymaster");

bindingSourceMarki.DataSource = markiQuery;    

Last line throws ArgumentNullException with ParamName:entity. When I change my code to this:

ObjectQuery<markimaster> markiQuery = context.markimaster.Include("modelemaster");

bindingSourceMarki.DataSource = markiQuery;

it work's (means doesn't throw exception), so i thought maybe there is row in typymaster that didn't have coresponding row in modelemaster, but checking database shows nothing.

Since I'm new to EntityFramework I have no idea what's wrong, so came here looking for advise ;)

[UPDATE]

I ran other query on my database:

select * from modelemaster where model_id not in (select model_id from typymaster)

which returns 2000 rows. So there are models that has no types.

[UPDATE]

This is fragment of my .edmx file

EntitySet Name="markimaster" EntityType="MMT_Master.store.markimaster"  store:Type="Tables" Schema="public" 
EntitySet Name="modelemaster" EntityType="MMT_Master.store.modelemaster" store:Type="Tables" Schema="public"
EntitySet Name="typymaster" EntityType="MMT_Master.store.typymaster" store:Type="Tables" Schema="public"

so it seems like names used in path passed to Include are correct

Answer 1

What happens when you change the first piece of code with

bindingSourceMarki.DataSource = markiQuery.Execute(MergeOption.AppendOnly);

? According to MSDN :

To bind objects to a Windows Form control, set the DataSource property of the control to the EntityCollection or to the ObjectResult that is returned when the Execute method is called on an ObjectQuery object .

Answer 2

The problem seems to be associated with the wrong EntitySet name.
Please check that you have passed the correct path to Include (maybe pluralization or case sensitivity issue).