VB.NET entities cause an exception with EE Core

[VBAndCs]

I published eShopOnWeb_VB.NET which is the VB.NET version of the Microsoft full web sample eShopOnWeb
The solution contains 3 projects:

1. Web.vb (a VB.NET ASP.NET Core 3.1 project).
2. Infrastructure.vb (a VB.NET .NET standard library project).
3. ApplicationCore.cs (a C# .NET standard library project):
   The repo also contains a VB.NET version named ApplicationCore.vb, but if you referenced it in the solution instead of the C# version, it will causes a runtime exception. I couldn't find the source of this exception, and I compared the C# and VB.Net versions of the project and they seems identical, with no obvious VB.NET special behavior that can cause the exception.
   This project contains the database entities and other classes used in query operations.
   This is the exception:

InvalidOperationException: Lambda expression used inside Include is not valid.
Microsoft.EntityFrameworkCore.Query.Internal.NavigationExpandingExpressionVisitor.ProcessInclude(NavigationExpansionExpression source, Expression expression, bool thenInclude)

What is the source of this exception?
Is there any EF convention that can be broken by different naming of properties backing fields or something similar?
Is it related to expression tree that VB generates?
How can I solve this?

[smitpatel]

Likely related to expression tree VB generated. Can you get print out of expression tree VB generates in C# world?

[VBAndCs]

@smitpatel
How can I get this expression tree?
And if it differs between C# and VB.NET, how can this be solved?
Thanks.

[VBAndCs]

Note: I see a note here says:

VBAndCs added the customer-reported label 8 minutes ago

I didn't do such a thing :)

[smitpatel]

That is template thing. I am not expert in VB but I think what you could do is

• Add a C# console app to your project.
• Write your query in VB project, instead of calling ToList or any other enumerating method, call a custom method which calls into C# project you add.
• In custom method inside C# project, take input of type IQueryable<T>. IQueryble.Expression would give you the expression tree backing the queryable. Print out of that would give us some hint how the tree is differing from C# tree.

[VBAndCs]

As I see, string comparison affects the expression trees. for example, in VB this lambda:
Function(b) b.Id = basketId

yields the expression:

Body = {(CompareString(b.BuyerId, value(Microsoft.eShopWeb.ApplicationCore.Specifications.BasketWithItemsSpecification+_Closure$__1-0).$VB$Local_buyerId, False) == 0)}

but in c#:

Body = {(b.BuyerId == value(Microsoft.eShopWeb.ApplicationCore.Specifications.BasketWithItemsSpecification+<>c__DisplayClass1_0).buyerId)}

Can this affect EF?
And how can I solve this?
I.e: How Can I convert VB expression tree to C#'s?
Or: How can I make EF accept VB's?

[smitpatel]

Duplicate of #19592

[VBAndCs]

@smitpatel
I don't have the same exception mentioned there, and I think there is more issues here.
Note the part
+_Closure$__1-0).$VB$Local_buyerId in VB which is
+<>c__DisplayClass1_0).buyerId in C#
Is this OK with EF?
There is more to investigate in my App, but it is better to go step by step.

[VBAndCs]

@smitpatel
I moved the string comparison to a separate function call, and this is the resulting expression:
Criteria = {basket => CompareStrings(basket.BuyerId, value(Microsoft.eShopWeb.ApplicationCore.Specifications.BasketWithItemsSpecification+_Closure$__1-0).$VB$Local_buyerId)}

I still get the same exception as before, so it is not due to the string comparison. Can it be the +_Closure$__1-0).$VB$Local_buyerId part?

[smitpatel]

Your last expression tree uses CompareStrings function rather than CompareString. Can you also post exception message?

[VBAndCs]

InvalidOperationException: Lambda expression used inside Include is not valid.
Microsoft.EntityFrameworkCore.Query.Internal.NavigationExpandingExpressionVisitor.ProcessInclude(NavigationExpansionExpression source, Expression expression, bool thenInclude)

[smitpatel]

Can you also share VB query? What is exactly inside include?

[VBAndCs]

I think this is the expression that causes the exception, because it is sent to include and the error occurs after pssing it:

In C#
b => b.Items
Yieds this expression:
b => b.Items

In VB:
Function(b) b.Items

Yieds this expression:
b=> Convert(b.Items, Object)

The Expression type is:
Expression<Func<T, object>>
'Expression(Of Func(Of T, Object))`

So, does the convert function in VB cause any issue with EF?
Does it expect object (with lower case o as the C# type) or System.Object?
Or does it refuse the conversion at all?