IIS ASP.NET 4.0的异常并在私有字段上使用反射

Question

We are having a problem with the following code when hosted in IIS running asp.net 4:

        DataTable dt = new DataTable();
        FieldInfo TableCaseSensitiveAmbientFieldInfo =
            typeof(DataTable).GetField("_caseSensitiveUserSet", BindingFlags.Instance | BindingFlags.NonPublic);
        TableCaseSensitiveAmbientFieldInfo.SetValue(dt, true);

The .SetValue() call fails with a FieldAccessException (this code is from a public source code file name ADONetHelper.cs which is used from a public source dll named CompactFormatterPlus)

This seems to only happen when hosted in IIS.

We believe it is due to a reflection/code access permission (after searching for an answer) but we have not found the right set of values to enable this code to work.

Any thoughts ?? Thanks, Fred

Answer 1

By default in IIS 7.0 applications are running in "medium trust". And ReflectionPermission is disabled by default with Medium Trust.

Medium Trust Summary

The main constraints placed on medium trust Web applications are: ... ReflectionPermission is not available. This means you cannot use reflection.

But seems like DataTable.CaseSensitive Property has a getter and a setter. I recoment that you keep away of reflection if at all possible. For example when you upgrade in future to another .NET framework that private method could be gone and your app will break.

If you are (de)serializing the DataSet and maybe a better idea would be to "manually" change "caseSensitiveAmbient" part in serialized XML.

Answer 2

Reflecting private members only works when the code runs under full trust. ASP .NET by default runs in medium trust.

Therefore, you need to configure your application to run in full trust for this to work.

How to do this is explained in this ASP .NET Trust Levels article, but basically you must add your assembly to the <fullTrustAssemblies> list under the <securityPolicy> element in web.config.