CodeAccessSecurityAttribute derived class throwing System.TypeLoadException (Failure has occurred while loading a type) - vb.net

Question

I have custom attribute applied to CRUD repository methods to control access:
Public Class SecureDbContextGenericRepository(Of TEntity As Class, TContext As DbContext)
Inherits DbContextGenericRepository(Of TEntity, TContext)
Public Sub New(connectionService As IConnectionService)
MyBase.New(connectionService)
End Sub
<EmployeeRoleRequirement(SecurityAction.Demand, EmployeeRoles:=EmployeeRoles.DataWriter)>
Public Overrides Sub Delete(ParamArray entities() As TEntity)
MyBase.Delete(entities)
End Sub
<EmployeeRoleRequirement(SecurityAction.Demand, EmployeeRoles:=EmployeeRoles.DataWriter)>
Public Overrides Sub Insert(ParamArray entities() As TEntity)
MyBase.Insert(entities)
End Sub
<EmployeeRoleRequirement(SecurityAction.Demand, EmployeeRoles:=EmployeeRoles.DataReader)>
Public Overrides Function [Select](Optional predicate As Func(Of TEntity, Boolean) = Nothing) As IList(Of TEntity)
Return MyBase.Select(predicate)
End Function
<EmployeeRoleRequirement(SecurityAction.Demand, EmployeeRoles:=EmployeeRoles.DataWriter)>
Public Overrides Sub Update(ParamArray entities() As TEntity)
MyBase.Update(entities)
End Sub
End Class
This is implementation of attribute:
Public Class EmployeeRoleRequirementAttribute
Inherits CodeAccessSecurityAttribute
Public Sub New(action As SecurityAction)
MyBase.New(action)
End Sub
Public Overrides Function CreatePermission() As IPermission
Return New EmployeeRolePermission(_EmployeeRoles)
End Function
Public Property EmployeeRoles As EmployeeRoles
End Class
<Flags>
Public Enum EmployeeRoles As Integer
DataReader = 0
DataWriter = 1
End Enum
And permission:
Public Class EmployeeRolePermission
Implements IPermission
Public Sub New(employeeRoles As EmployeeRoles)
_EmployeeRoles = employeeRoles
End Sub
Public Function Copy() As IPermission Implements IPermission.Copy
Return New EmployeeRolePermission(_EmployeeRoles)
End Function
Public Sub Demand() Implements IPermission.Demand
Dim principal = DirectCast(Thread.CurrentPrincipal, ProductionAssistantPrincipal)
If Not principal.IsInRole(_EmployeeRoles) Then
Throw New SecurityException(String.Format(My.Resources.EmployeeRoleNotFound,
principal.Identity.Name,
_EmployeeRoles.ToString()))
End If
End Sub
Public Sub FromXml(e As SecurityElement) Implements ISecurityEncodable.FromXml
Throw New NotImplementedException()
End Sub
Public Function Intersect(target As IPermission) As IPermission Implements IPermission.Intersect
Return New EmployeeRolePermission(_EmployeeRoles And DirectCast(target, EmployeeRolePermission).EmployeeRoles)
End Function
Public Function IsSubsetOf(target As IPermission) As Boolean Implements IPermission.IsSubsetOf
Return _EmployeeRoles.HasFlag(DirectCast(target, EmployeeRolePermission).EmployeeRoles)
End Function
Public Function ToXml() As SecurityElement Implements ISecurityEncodable.ToXml
Throw New NotImplementedException()
End Function
Public Function Union(target As IPermission) As IPermission Implements IPermission.Union
Return New EmployeeRolePermission(_EmployeeRoles Or DirectCast(target, EmployeeRolePermission).EmployeeRoles)
End Function
Public ReadOnly Property EmployeeRoles As EmployeeRoles
End Class
Every time one of the CRUD methods are reached, TypeLoadException is thrown. I really dont know cause of this, but if I remove attributes from CRUD methods, everything works fine.

Answer 1

This seems to be due to the enum-valued property on the attribute (see https://connect.microsoft.com/VisualStudio/feedback/details/596251/custom-cas-attributes-with-an-enum-property-set-cause-a-typeloadexception for details). To work around this issue, you could use a string-valued property on the attribute and cast to an enum either in the property setter or just before creating the permission. (Personally, I'd probably opt for the former in the interests of enabling early validation, but ymmv...)

Answer 2

Another workaround is making attribute property of type, which is used in Enum, in this case Integer.
Public Class EmployeeRoleRequirementAttribute
Inherits CodeAccessSecurityAttribute
Public Sub New(action As SecurityAction)
MyBase.New(action)
End Sub
Public Overrides Function CreatePermission() As IPermission
Return New EmployeeRolePermission(CType(_RequiredEmployeeRoles, EmployeeRoles))
End Function
Public Property RequiredEmployeeRoles As Integer
End Class
<Flags>
Public Enum EmployeeRoles As Integer
DataReader = 0
DataWriter = 1
End Enum
Then you dont need to use String, which does not allow easy combining of flags when attribute is used:
<EmployeeRoleRequirement(SecurityAction.Demand, RequiredEmployeeRoles:=EmployeeRoles.DataReader Or EmployeeRoles.DataWriter)>
Sub SecuredMethod()
End Sub