HashSet(Of T) - how can I get elements by position number ?

dilkonika

Sorry Friend. It's my mistake. Now it's confirmed : The CloneEntity Function is working correctly when I pass the element that I get from the expression :

Dim element = CType(Enumerable.ElementAt(CallByName(MyObj1, "Child1", CallType.Get), k), Child1)

But is not working correctly when I pass the element that I get from this expression :

Dim element = CTypeDynamic(Enumerable.ElementAt(CallByName(MyObj1, "Child1", CallType.Get), k), Type.GetType("MyProg1.Child1,MyProg1,Version=1.0.0, Culture=neutral,PublicKeyToken=null"))

Sascha Lefevre

Yes, in the meantime I replicated it - both versions, simplified here:

Dim el = Enumerable.ElementAt(CallByName(MyClass, "Children", CallType.Get), 1)

REM 1
Dim el1 = CType(el, ChildClass)
Dim el1copy = CopyEntity(el1) REM works. (el1copy is of type ChildClass)

REM 2
Dim el2 = CTypeDynamic(Of ChildClass)(el)
Dim el2copy = CopyEntity(el2) REM works. (el2copy is of type ChildClass)

REM 3
Dim el3 = CTypeDynamic(el, GetType(ChildClass))
Dim el3copy = CopyEntity(el3) REM doesn't work. (el3copy is of type Object)

That's basically the same as your code above. And it's still the same as what I'm talking about for the last messages ;P I know you can't use 1 and 2. The reason they work is because the return type of CType(el, ChildClass) and CTypeDynamic(Of ChildClass)(el) is ChildClass. The reason 3 doesn't work is because the return type of CTypeDynamic(el, GetType(ChildClass)) is Object (so it doesn't have anything to do with Type.GetType(..)). So, for 1 and 2 CopyEntity(..) is called for the correct generic type, for 3 it's called with Object as generic type. I don't know if there's a way to make 3 work. I tested the same thing (as 3) in C# and it actually works. Either VB differs there from C# or I just don't know how to do it in VB. I can assure you though that the reflection-approach that I suggested would work. If you want to find out if there is a way to make 3 work I would suggest you post a new question so that someone who knows VB better than me will be more likely to notice.

If the brain were so simple we could understand it, we would be so simple we couldn't. — Lyall Watson

dilkonika

Thank you ! Please , can you post here the code ( of variant 3 ) that works on C# ? ( I mean the whole code that you have tested , with the Copyentity function too ). Thank you !

Sascha Lefevre

Sure, here you go:

class ChildClass
{ }

class MyClass
{
public ICollection<ChildClass> Children { get; set; }

public MyClass()
{
    Children = new HashSet<ChildClass>() { new ChildClass() };
}

}

T CopyEntity(T entity)
where T : class, new()
{
T copy = new T();
// actual copying omitted here
// for testing only the return type matters
return copy;
}

void Test()
{
MyClass myClass = new MyClass();
dynamic children = typeof(MyClass).GetProperty("Children").GetValue(myClass);
dynamic child = Enumerable.ElementAt(children, 0);
dynamic copy = CopyEntity(child);
// copy is of type ChildClass
}

If the brain were so simple we could understand it, we would be so simple we couldn't. — Lyall Watson

dilkonika

Thank you ! But your code in C# when is converted in vb.net ( with code converters ) , is :

Class ChildClass
End Class

Class [MyClass]
Public Property Children() As ICollection(Of ChildClass)
Get
Return m_Children
End Get
Set
m_Children = Value
End Set
End Property
Private m_Children As ICollection(Of ChildClass)

Public Sub New()
	Children = New HashSet(Of ChildClass)() From { \_
		New ChildClass() \_
	}
End Sub

End Class

Private Function CopyEntity(Of T As {Class, New})(entity As T) As T
Dim copy As New T()
' actual copying omitted here
' for testing only the return type matters
Return copy
End Function

Private Sub Test()
Dim [myClass] As New [MyClass]()
Dim children As dynamic = GetType([MyClass]).GetProperty("Children").GetValue([myClass])
Dim child As dynamic = Enumerable.ElementAt(children, 0)
Dim copy As dynamic = CopyEntity(child)
' copy is of type ChildClass
End Sub

and this code is not using CTypeDynamic. So what you have tested in vb.net that doesn't work ? and on my vb.net code , the error came up on the line :

Dim en = ctx.Entry(clone)

and you don't have a such line in your code. ............................. Also I try to implement your version with reflection , but I can't make it work on vb.net ? can you provide some more help ? .............................. Thank you !

Sascha Lefevre

dilkonika wrote:

and this code is not using CTypeDynamic.

Because it works without it. For completeness, I included the analog into the VB-version:

Public Class ChildClass
End Class

Public Class SomeClass
    Public Property Children As ICollection(Of ChildClass) = New HashSet(Of ChildClass)
End Class

Public Function CopyEntity(Of T As {Class, New})(entity As T) As T
    Dim clone As New T()
    Return clone
End Function

Sub Main()
    Dim someClass = New SomeClass
    someClass.Children.Add(New ChildClass)

    Dim el = Enumerable.ElementAt(CallByName(someClass, "Children", CallType.Get), 0)

    Dim elcopy = CopyEntity(el)   REM without CTypeDynamic. doesn't work. (elcopy is Object)

    Dim el1 = CType(el, ChildClass)
    Dim el1copy = CopyEntity(el1) REM works (el1copy is ChildClass)

    Dim el2 = CTypeDynamic(Of ChildClass)(el)
    Dim el2copy = CopyEntity(el2) REM works (el2copy is ChildClass)

    Dim el3 = CTypeDynamic(el, GetType(ChildClass))
    Dim el3copy = CopyEntity(el3) REM doesn't work (el3copy is Object)
End Sub

Quote:

and on my vb.net code , the error came up on the line : Dim en = ctx.Entry(clone) and you don't have a such line in your code.

Because the reason why it not works (when it not works) is because clone is of type Object and not of type ChildClass. So I only have to check for the type of clone to know if your line ctx.Entry(clone) would work.

dilkonika wrote:

Also I try to implement your version with reflection , but I can't make it work on vb.net ? can you provide some more help ?

Please post what you have so far.

If the brain were so simple we could understand it, we would be so simple we couldn't. — Lyall Watson

dilkonika

Thank you ! But for the Reflection version , I just converted the code to vb.net but I don't know how to integreate with my code. If you can just post your full version for C# with reflection so I can understand more ( I don't have so much knowledge about reflection , but at this point I really need a solution for my problem , so I need to use it )

Sascha Lefevre

class Program
{
class ChildClass
{ }

class SomeClass
{
    public ICollection Children { get; set; }

    public SomeClass()
    {
        Children = new HashSet() { new ChildClass() };
    }
}

public static T CopyEntity(T entity)
    where T : class, new()
{
    T copy = new T();
    return copy;
}

static void Main(string\[\] args)
{
    SomeClass someClass = new SomeClass();

    dynamic children = typeof(SomeClass).GetProperty("Children").GetValue(someClass);
    object child = Enumerable.ElementAt(children, 0);

    // if CopyEntity would be not a static method, BindingFlags.Instance
    // would have to be used, instead of BindingFlags.Static 
    MethodInfo mi = typeof(Program).GetMethod("CopyEntity", BindingFlags.Static | BindingFlags.Public);
    mi = mi.MakeGenericMethod(new Type\[\] { /\* +typeof(YourContext) \*/ child.GetType() /\* +typeof(bool) \*/ });

    // if CopyEntity would be not a static method, the first argument
    // to Invoke would have to be the class-instance on which to invoke
    // CopyEntity, instead of null
    object clone = mi.Invoke(null, new object\[\] { /\* +ctx \*/ child /\* +copyKeys \*/ });
    // -> clone is of type ChildClass
}

}

If the brain were so simple we could understand it, we would be so simple we couldn't. — Lyall Watson

dilkonika

Thank you ! Your code is working. Just for curiosity , the other variant is working too. I found this solution in vb.net , to make a change on CopyEntityFunction like this : instead of

Dim clone as New(T)

I use this :

Dim clone = Activator.CreateInstance(entity.GetType())

Now it's working. Thank you for your help.

Sascha Lefevre

dilkonika wrote:

Dim clone = Activator.CreateInstance(entity.GetType())

Yes, that's a simpler solution if you don't need CopyEntity to be generic (that is, if you don't need the static type T for anything else). If you haven't already, you can remove that generic stuff from the declaration of CopyEntity then.

dilkonika wrote:

Thank you for your help.

You're welcome.

If the brain were so simple we could understand it, we would be so simple we couldn't. — Lyall Watson