Question

In ASP.NET MVC2 I use OutputCache and the VaryByParam attribute. I got it working fine with a single parameter, but what is the correct syntax when I have several parameters on the method?

[OutputCache(Duration=30, VaryByParam = "customerId"]
public ActionResult Index(int customerId)
{
//I've got this one under control, since it only has one parameter
}

[OutputCache(Duration=30, VaryByParam = "customerId"]
public ActionResult Index(int customerId, int languageId)
{
//What is the correct syntax for VaryByParam now that I have a second parameter?
}

How do I get it to cache the pages using both parameters? Do I enter add the attribute twice? Or write “customerId, languageId” as the value??

Answer 1

Valid values for VaryByParam are one of the following:

• The literal string * (asterisk), which varies by all parameters of the action method.
• The literal string none (case-insensitive), which varies by no parameters of the action method.
• A string containing the semicolon-separated names of the parameters you wish to vary by.

In your case, you’d want the first option:

[OutputCache(Duration = 30, VaryByParam = "*")]
public ActionResult Index(int customerId, int languageId)
{
}

If, however, you had some params you want to vary by and some that you don’t, then you’d use the third option:

[OutputCache(Duration = 30, VaryByParam = "customerId;languageId")] // foo is omitted
public ActionResult Index(int customerId, int languageId, int foo)
{
}

Reference.