Entity Framework : Error when trying to Deep clone an object - vb.net

Question

I'm using Entity Framework 6 , with Database First. The model is created using wizard from existing Sql server database.
I'm using this code to do a deep clone :
Imports System.ComponentModel
Imports System.Collections
Imports System.Data.Entity.Core.Objects.DataClasses
Imports System.Runtime.Serialization
Imports System.IO
Imports System.Reflection
Imports System.Runtime.CompilerServices
Module Extensions
Private Function ClearEntityObject(Of T As Class)(ByVal source As T, ByVal bCheckHierarchy As Boolean) As T
If (source Is Nothing) Then
Throw New Exception("Null Object cannot be cloned")
End If
Dim tObj As Type = source.GetType
If (Not tObj.GetProperty("EntityKey") Is Nothing) Then
tObj.GetProperty("EntityKey").SetValue(source, Nothing, Nothing)
End If
If bCheckHierarchy Then
Dim PropertyList As List(Of PropertyInfo) = Enumerable.ToList(Of PropertyInfo)((From a In source.GetType.GetProperties
Where a.PropertyType.Name.Equals("ENTITYCOLLECTION`1", StringComparison.OrdinalIgnoreCase)
Select a))
Dim prop As PropertyInfo
For Each prop In PropertyList
Dim keys As IEnumerable = DirectCast(tObj.GetProperty(prop.Name).GetValue(source, Nothing), IEnumerable)
Dim key As Object
For Each key In keys
Dim childProp As EntityReference = Enumerable.SingleOrDefault(Of PropertyInfo)((From a In key.GetType.GetProperties
Where (a.PropertyType.Name.Equals("EntityReference`1", StringComparison.OrdinalIgnoreCase))
Select a)).GetValue(key, Nothing)
ClearEntityObject(childProp, False)
ClearEntityObject(key, True)
Next
Next
End If
Return source
End Function
<Extension()> _
Public Function ClearEntityReference(ByVal source As Object, ByVal bCheckHierarchy As Boolean) As Object
Return ClearEntityObject(source, bCheckHierarchy)
End Function
<Extension()> _
Public Function Clone(Of T)(ByVal source As T) As T
Dim ser As New DataContractSerializer(GetType(T))
Using stream As MemoryStream = New MemoryStream
ser.WriteObject(stream, source)
stream.Seek(0, SeekOrigin.Begin)
Return DirectCast(ser.ReadObject(stream), T)
End Using
End Function
End module
Now , I try to use this code like this :
Private Sub DoClone
Dim litm, newitm As MyObject
litm = context.MyObjects.FirstOrDefault
newitm = litm.Clone()
newitm.ClearEntityReference(True)
context.MyObjects.Add(newitm)
context.SaveChanges()
End Sub
I get an error :
An unhandled exception of type
'System.Runtime.Serialization.SerializationException' occurred in
System.Runtime.Serialization.dll
Additional information:Type
'System.Data.Entity.DynamicProxies.MyObject_F2FFE64DA472EB2B2BDF7E143DE887D3845AD9D1731FD3107937062AC0C2E4BB'
with data contract name
'MyObject_F2FFE64DA472EB2B2BDF7E143DE887D3845AD9D1731FD3107937062AC0C2E4BB:http://schemas.datacontract.org/2004/07/System.Data.Entity.DynamicProxies'
is not expected.
Consider using a DataContractResolver or add any
types not known statically to the list of known types - for example,
by using the KnownTypeAttribute attribute or by adding them to the
list of known types passed to DataContractSerializer.
This is my model that I use :
Partial Public Class Myobject
Public Property id As Integer
Public property name as string
Public Overridable Property chld As ICollection(Of chld) = New HashSet(Of chld)
Public Overridable Property chld1 As ICollection(Of chld1) = New HashSet(Of chld1)
End Class
Partial Public Class chld
Public Property id As Integer
Public Property date1 as DateTime
Public Property quantity as Integer
Public Property ParentID as integer
Public Overridable Property MyObj1 As MyObject
End Class
Partial Public Class chld1
Public Property id As Integer
Public Property nm as string
Public Property ParentID as integer
Public Overridable Property MyObj1 As MyObject
End Class