Matthieu MEZIL : Bug

C# compiler and implicit keyword: can be better

Matthieu MEZIL — Mon, 03 Nov 2008 07:51:00 GMT

Imagine the following code:

class A
{
    public static implicit operator B(A a)
    {
        return new B(a);
    }
}
class B
{
    public B(A a)
    {
    }
}

This code compile without error and it's normal.

Now imagine the following one:

class A
{
    public static implicit operator B(A a)
    {
        return new A();
    }
}

The compiler generates no error with this code but it should!

Less annoying, the compiler generates an error with this code (Cannot implicitly convert type 'A' to 'C') even though it would be able to use B to convert A to C:

class Program
{
    static void Main(string[] args)
    {
        C c = new A();
    }
}
 
class A
{
    public static implicit operator B(A a)
    {
        return new B(a);
    }
}
class B
{
    public B(A a)
    {
    }
 
    public static implicit operator C(B b)
    {
        return new C(b);
    }
}
 
class C
{
    public C(B b)
    {
    }
}

Bug with IQueryable and yield syntax: System.BadImageFormatException "An attempt was made to load a program with an incorrect format. (Exception from HRESULT: 0x8007000B)"

Matthieu MEZIL — Tue, 14 Oct 2008 08:15:00 GMT

I find a bug if you mix IQueryable and yield syntax.

After Diego has changed a little bit my sample to reproduce it, this is the code he sent to the C# team:

class Program
{
    static void Main(string[] args)
    {
        try
        {
            GetCategoryProductsUsingQueryable(() => new MyProduct(), 1).ToList();
            Console.WriteLine("Queryable succeeds");
        }
        catch (Exception e)
        {
            LogException(e);
        }
    }
 
    private static void LogException(Exception e)
    {
        Console.WriteLine(e.GetType());
        Console.WriteLine(e.Message);
    }
 
 
    private static List<Category> Categories =
        new List<Category> { 
            new Category { 
                CategoryID = 1, 
                Products = new List<Product> { 
                    new Product { 
                        ProductID = 1 } } } };
 
 
    static IEnumerable<P> GetCategoryProductsUsingQueryable<P>(Func<P> newP, int categoryId) where P : IProduct
    {
        var categ = Categories.AsQueryable().FirstOrDefault(c => c.CategoryID == categoryId);
        if (categ == null)
            yield break;
        foreach (var p in categ.Products)
            yield return Load(newP(), p);
    }
 
    static P Load<P>(P item, Product p) where P : IProduct
    {
        item.ID = p.ProductID;
        return item;
    }
}
 
public interface IProduct
{
    int ID { get; set; }
}
 
public class MyProduct : IProduct
{
    public int ID { get; set; }
}
 
public class Category
{
    public int CategoryID { get; set; }
    public List<Product> Products { get; set; }
}
public class Product
{
    public int ProductID { get; set; }
}

In this case, the console output is:

System.BadImageFormatException
An attempt was made to load a program with an incorrect format. (Exception from HRESULT: 0x8007000B)

TPT with designer can generate errors 3034 or 3021

Matthieu MEZIL — Wed, 17 Sep 2008 08:19:00 GMT

I found two cases of errors generated by the EDM designer when you want to do TPT.

Error 3034:

Imagine the following scenario:

A table Contacts
- ContactID (PK)
A table Employees
- ContactID (PK)
- OfficeID (Nullable, FK to Offices.OfficeID)
A table Offices
- OfficeIF (PK)

To do TPT between Contacts and Employees with designer, I do the following:

I delete the relationship between Employees and Contacts.
I also delete Employees.EmployeeID property.
Then I add inheritance between Employees and Contacts.
Then, always with designer, I remap the Employees entity type and the relationship between Employees and Offices

Here I have an error because the designer "forgets" the condition IsNull=false in the relationship mapping.

Error 3021

Imagine the following scenario:

A table Contacts
- ContactID (PK)
A table Employees
- ContactID (PK)
A table Hodidays
- EmployeeID (PK, KF to Employees.ContactID)
- From (PK)

I want to do TPT as previously.

In this case, I have an error 3021 because the designer "forgets" the CSDL association ReferentialConstraint which is inevitable if the FK is in the PK.

So ok, there are some bugs in the designer but don't forget that designer is just here for help. So these bugs don't prevented you to use EF.

Reflector IL to C# Bug

Matthieu MEZIL — Wed, 04 Jun 2008 17:05:00 GMT

I was watching Entity Framework code when I found this code:

switch (this.<>1__state)
{
    case 3:
    case 4:
        break;

    default:
        return;
        try
        {
        }
        finally
        {
            this.d__0.<>m__Finally6();" href="http://www.aisto.com/roeder/dotnet/Default.aspx?Target=code://System.Data.Entity:3.5.0.0:b77a5c561934e089/System.Data.EntityModel.SchemaObjectModel.EntityContainerAssociationSet.d__0/<>m__Finally6()"><>m__Finally6();
        }
        break;
}

Very strange. It was the same with VB.Net. So I watched IL and I undestood that Reflector has a bug.

Indeed the IL was next:

L_0023: ldfld int32 System.Data.EntityModel.SchemaObjectModel.EntityContainerAssociationSet/<get_Ends>d__0::<>1__state
L_0028: stloc.1
L_0029: ldloc.1
L_002a: ldc.i4.3
L_002b: sub
L_002c: switch (L_003a, L_003a)
L_0039: ret
L_003a: leave.s L_0043
L_003c: ldarg.0
L_003d: call instance void System.Data.EntityModel.SchemaObjectModel.EntityContainerAssociationSet/<get_Ends>d__0::<>m__Finally6()
L_0042: endfinally
L_0043: ret
.try L_003a to L_003c finally handler L_003c to L_0043

So C# code should be:

switch (this.<>1__state)
{
    case 3:
    case 4:
        try
        {
        }
        finally
        {
            this.d__0.<>m__Finally6();" href="http://www.aisto.com/roeder/dotnet/Default.aspx?Target=code://System.Data.Entity:3.5.0.0:b77a5c561934e089/System.Data.EntityModel.SchemaObjectModel.EntityContainerAssociationSet.d__0/<>m__Finally6()"><>m__Finally6();
        }
        break;
    default:
        return;
}

Reflector Bug with generics

Matthieu MEZIL — Wed, 04 Jun 2008 14:33:00 GMT

For this code:

class A<T>
{
    public A()
    {
        var b = new B();
    }
    class B : A<T>
    {
    }
}

Reflector generates this:

class A<T>
{
    public A()
    {
        var b = new B<T>();
    }
    class B : A<T>
    {
    }
}

which isn't correct.