Last week we published the RC2 build of ASP.NET MVC 3.  I blogged a bunch of details about it here.

One of the reasons we publish release candidates is to help find those last “hard to find” bugs. So far we haven’t seen many issues reported with the RC2 release (which is good) - although we have seen a few reports of a metadata caching bug that manifests itself in at least two scenarios:

• Nullable parameters in action methods have problems: When you have a controller action method with a nullable parameter (like int? – or a complex type that has a nullable sub-property), the nullable parameter might always end up being null - even when the request contains a valid value for the parameter.

• [AllowHtml] doesn’t allow HTML in model binding: When you decorate a model property with an [AllowHtml] attribute (to turn off HTML injection protection), the model binding still fails when HTML content is posted to it.

Both of these issues are caused by an over-eager caching optimization we introduced very late in the RC2 milestone.  This issue will be fixed for the final ASP.NET MVC 3 release.  Below is a workaround step you can implement to fix it today.

Workaround You Can Use Today

You can fix the above issues with the current ASP.NT MVC 3 RC2 release by adding one line of code to the Application_Start() event handler within the Global.asax class of your application:

The above code sets the ModelMetaDataProviders.Current property to use the DataAnnotationsModelMetadataProvider.  This causes ASP.NET MVC 3 to use a meta-data provider implementation that doesn’t have the more aggressive caching logic we introduced late in the RC2 release, and prevents the caching issues that cause the above issues to occur. 

You don’t need to change any other code within your application.  Once you make this change the above issues are fixed.  You won’t need to have this line of code within your applications once the final ASP.NET MVC 3 release ships (although keeping it in also won’t cause any problems).

Hope this helps – and please keep any reports of issues coming our way,

Scott

P.S. In addition to blogging, I am also now using Twitter for quick updates and to share links. Follow me at: twitter.com/scottgu