OutputCache with VaryByCustom not working

Question

I am trying to implement caching in ASP.NET MVC 4 using the OutputCache attribute.

Here is my controller action:

[HttpGet]
[OutputCache(Duration = CACHE_DURATION, VaryByCustom = "$LanguageCode;myParam", Location = OutputCacheLocation.Server)]
public JsonResult MyAction(string myParam)
{
    // this is called also if should be cached!
}

And here is GetVaryByCustomString in Global.asax:

public override string GetVaryByCustomString(HttpContext context, string arg)
{
    var pars = arg.Split(';');
    if (pars.Length == 0) return string.Empty;

    var res = new System.Text.StringBuilder();
    foreach (var s in pars)
    {
        switch (s)
        {
            case "$LanguageCode":
                var culture = CultureManager.GetCurrentCulture();
                res.Append(culture.Name);
                break;
            default:
                var par = context.Request[s];
                if (par != null)
                    res.AppendFormat(par);
                break;
        }
    }
    return base.GetVaryByCustomString(context, res.ToString());
}

This method is always called and returns the correct value (for example, "it123").

If I call an action with only a single parameter myParam, the cache works correctly.

http://localhost:1592/MyController/MyAction?myParam=123 // called multiple times always read from cache

The problem is that when I call an action with another parameter not included in the string VaryByCustom, the controller action is called anyway, also if it should be cached, but GetVaryByCustomStringreturns the same result.

http://localhost:1592/MyController/MyAction?myParam=123&dummy=asdf // called multiple times with different 'dummy' values always calls the action

Any idea?

Answer 1

[OutputCache], VaryByParam="":

[OutputCache(Duration = CACHE_DURATION, VaryByCustom = "$LanguageCode;myParam", VaryByParam = "", Location = OutputCacheLocation.Server)]

"*" (All).

GetVaryByCustomString() :

return res.ToString();

base.GetVaryByCustomString():

public virtual string GetVaryByCustomString(HttpContext context, string custom) {

        if (StringUtil.EqualsIgnoreCase(custom, "browser")) {
            return context.Request.Browser.Type;
        }

        return null;
    }

, , , , , , null, string, .

( , [OutputCache] , )