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

Sascha Lefevre

ElementAt(..) is an extension-method and these aren't supported for dynamic typing (which is what you're doing because the return type of CallByName(..) is Object). However, you can either cast the returned object to the actual type and then call the extension method on it:

CType(CallByName(MyObject, "Child1", CallType.Get), HashSet(Of Child1)).ElementAt(k)

..or you can pass the object to Enumerable.ElementAt(..) as a parameter:

Enumerable.ElementAt(CallByName(MyObject, "Child1", CallType.Get), k)

dilkonika

Thank you ! sorry , but if you can understand , I want to use an expression where all are variables. So Myobject is a variable , the navigation property's name is a variable ( a list of strings like "child1" that is filled on runtime ). But if I include a know type like Hashset(of Child1) then I can't realize my goal. so my final scope is to have a scenario like this : Dim varobject ------------ ( this will hold an object from Entity ). Dim l as list(of String)----- ( This will hold childs Navigation properties name as string ). And I want an expression like this : CallByname(Varobject,l(0),CallType.Get).ElementAt(k) ( of course when this expression will be used , the varobject will be an object from entity , and the list will hold navigation;s properties name that exist on varobject.( I have realized this scenario with count like this : CallByname(Varobject,l(0),CallType.Get).Count , but I don't know hot to realize for the problem I have described ) So for this reason I can't use your solution. is there any other way I can use ? Thank you !

Sascha Lefevre

I edited my previous answer, please take a look. The second option should be what you need.

dilkonika

Thank you ! I don't know if you last solution works correctly, but after I get the element with your code :

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

I have a code like this :

Public Function CopyEntity(Of T As {Class, New})(ctx As MyEntities, entity As T, Optional copyKeys As Boolean = False) As T
Dim clone As New T()
Dim en = ctx.Entry(clone)
en.State = System.Data.Entity.EntityState.Added
ctx.Entry(clone).CurrentValues.SetValues(entity)
en.State = System.Data.Entity.EntityState.Detached
Return clone
End Function

and I pass the element I get with your code like this :

fhitm = CopyEntity(context, element,False)

I get an error on the line Dim en = ctx.Entry(clone) :

An unhandled exception of type 'System.InvalidOperationException' occurred in EntityFramework.dll

Additional information: The entity type Object is not part of the model for the current context.

I thought to using CTypeDynamic in order to cast the element to correct type, but as I wrote , I have only a string "Child1" and I have used :

CTypeDynamic(Element,System.Type.Gettype("Child1"))

, but the expression

System.Type.Gettype("Child1")

always return Nothing.

Sascha Lefevre

This is a bit speculation because I don't have a lot of experience with dynamic typing. But I'm almost sure about it:

Dim element = Enumerable.ElementAt(CallByName(MyObject, "Child1", CallType.Get), k)
REM "element" actually is of the type the elements of Child1 have
REM but at this point it's treated as type Object

REM so this generic function is called for the generic type Object
Public Function CopyEntity(Of T As {Class, New})(ctx As MyEntities, entity As T, ...) As T
REM so "clone" actually is created as just an Object and not of the same type as "element" / "entity"
Dim clone As New T()
REM and the type Object of course isn't a valid entity-type in your context
Dim en = ctx.Entry(clone)

Your options: 1) An ugly if-else-cascade for all potential types of entities where you test for the actual type of the entity and call CopyEntity(..) with an according cast. 2) Reflection. C#-sample here (last time you said you could read it - otherwise please ask):

// CEClass : class that contains the function CopyEntity
// CEInstance : an instance of CEClass

MethodInfo mi = typeof(CEClass).GetMethod("CopyEntity");
mi = mi.MakeGenericMethod(typeof(MyEntities), element.GetType(), typeof(bool));
// you could cache "mi"

object clone = mi.Invoke(CEInstance, new object[] {context, element, false});

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

dilkonika

"REM so "clone" actually is created as just an Object and not of the same type as "element" / "entity"

This is not true because I try to use this instruction :

Ctype(element,Child1)

--- and after that everything works correctly But as I have explained , I can't use this kind of cast because I don't have the type Child1. I have only the string "Child1". For that I try to use CTypeDynamic. So I want to know why this line :

System.Type.Gettype("Child1")

produce Nothing ? Because with default types like "Integer" is working.

Sascha Lefevre

dilkonika wrote:

This is not true because I try to use this instruction : --- and after that everything works correctly

If we don't misunderstand each other here, this is what I would expect because you're casting element to its actual type, so CopyEntity(..) will be called for the actual type, so Dim clone As New T() will not create clone as Object but as the same type as element. So this is essentially what I presented as your first option. The reason why Type.Gettype("Child1") doesn't work is because you have to specify more than just the name of the class, please refer to MSDN[^]. But CTypeDynamic(..) won't help you because it requires the requested target-type as a static type argument, which you don't have and won't get with Type.Gettype(..). So it's still option 1 or 2 :)

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

dilkonika

as I have read ion this link https://msdn.microsoft.com/en-us/library/ee835926(v=vs.110).aspx[^] , the type specified as parameter inside CtypeDynamic , may be a variable. Inside this link there;s an example that use Gettype inside the CTypeDynamic. and for the type.Gettype , I read that I have to use the namespace together with my string;s name type. But where can I find the namespace for my entity object ?

Sascha Lefevre

dilkonika wrote:

the type specified as parameter inside CtypeDynamic

That version of CTypeDynamic(..) won't help you either because it returns Object.

dilkonika wrote:

But where can I find the namespace for my entity object ?

In the source file where it's declared? :confused: Alternatively by looking at entity.GetType().FullName[^] Why don't you try my suggested Reflection-approach?

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

dilkonika

For namespace I'm asking because I try to use the name where it was declared but doesn't work. In the link for Type.Gettype , I found that I need the AssemblyQualifiedName. Is this the namespace + the name of class ?? for this I'm confused.

Sascha Lefevre

On the page for Type.GetType are links to Type.AssemblyQualifiedName[^] where this is documented.

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

dilkonika

Yes , now I'm using this code :

Dim t a type
Dim s as string = "MyProg1.Child1,MyProg1,Version=1.0.0, Culture=neutral,PublicKeyToken=null"
t=System.Type.GetType(s)

But the problem is that the t get this value : "MyProg1.Child1" , I'm expecting to have just "Child1" What's the problem ?

Sascha Lefevre

It's one and the same; unless you have multiple classes named "Child1" in your solution, then "Child1" may or may not be the same as "MyProg1.Child1".

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

dilkonika

Ok , but then why when I use :

CTypeDynamic(Element,Child1)

everything is ok with my CopyEntity function. Whe I use :

Dim t a type
Dim s as string = "MyProg1.Child1,MyProg1,Version=1.0.0, Culture=neutral,PublicKeyToken=null"
t=System.Type.GetType(s)
CtypeDynamic(Element,t)

I'm still getting the error :

An unhandled exception of type 'System.InvalidOperationException' occurred in EntityFramework.dll

Additional information: The entity type Object is not part of the model for the current context.

Sascha Lefevre

I'm trying to replicate it.. it's not actually CTypeDynamic(Element,Child1) how your working code looks like, is it? Is it CTypeDynamic(Element, GetType(Child1)) or CTypeDynamic<Child1>(Element) ?

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

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 !