CodeAccessSecurityAttribute派生類投擲System.TypeLoadException（在加載類型已發生故障）

Question

我已經自定義屬性應用到CRUD庫的方法來控制訪問：

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 

這是實現屬性：

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 

和權限：

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 

每次之一CRUD方法已經到達，拋出了TypeLoadException。我真的不知道這個原因，但如果我從CRUD方法中刪除屬性，一切正常。

Answer 1

這似乎是由於屬性上的枚舉值屬性（有關詳細信息，請參閱https://connect.microsoft.com/VisualStudio/feedback/details/596251/custom-cas-attributes-with-an-enum-property-set-cause-a-typeloadexception）。要解決此問題，可以在屬性上使用字符串值屬性，並在屬性設置器中或在創建權限之前將其強制轉換爲枚舉。 （就我個人而言，我可能會選擇前者來實現早期驗證，但是ymmv ...）

Answer 2

另一個解決方法是製作用於Enum中的屬性屬性，在此情況下爲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 

然後你不需要用String，不允許容易標誌組合使用時，屬性：

<EmployeeRoleRequirement(SecurityAction.Demand, RequiredEmployeeRoles:=EmployeeRoles.DataReader Or EmployeeRoles.DataWriter)> 
Sub SecuredMethod() 
End Sub