CodeAccessSecurityAttribute派生类投掷System.TypeLoadException（在加载类型已发生故障）

Question

我已经自定义属性应用到CRUD库的方法来控制访问：

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 

这是实现属性：

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 

和权限：

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方法已经到达，抛出了TypeLoadException。我真的不知道这个原因，但如果我从CRUD方法中删除属性，一切正常。

Answer 1

这似乎是由于属性上的枚举值属性（有关详细信息，请参阅https://connect.microsoft.com/VisualStudio/feedback/details/596251/custom-cas-attributes-with-an-enum-property-set-cause-a-typeloadexception）。要解决此问题，可以在属性上使用字符串值属性，并在属性设置器中或在创建权限之前将其强制转换为枚举。 （就我个人而言，我可能会选择前者来实现早期验证，但是ymmv ...）

Answer 2

另一个解决方法是制作用于Enum中的属性属性，在此情况下为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 

然后你不需要用String，不允许容易标志组合使用时，属性：

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