ASP.NET MVC SessionStateBehavior

CustomControllerFactory.cs

public class CustomControllerFactory : DefaultControllerFactory
{
    protected override SessionStateBehavior GetControllerSessionBehavior(RequestContext requestContext, Type controllerType)
    {
        if (requestContext.HttpContext.Request.IsAjaxRequest())
        {
            // ajax の場合はセッションを読み取り専用にする
            return SessionStateBehavior.ReadOnly;
        }
        return base.GetControllerSessionBehavior(requestContext, controllerType);
    }
}

Global.asax.cs

public class MvcApplication : System.Web.HttpApplication
{
    protected void Application_Start()
    {
        ・・・
        
        ControllerBuilder.Current.SetControllerFactory(new CustomControllerFactory());
    }
}