Can you set OutputCache Tag dynamically in .NET 8?

Question

I'm building an ASP.NET Core 8 MVC site relying on OutputCache. The implementations is pretty standard and works just fine.

E.g.

[OutputCache(PolicyName = "MyCachePolicy")]
public ActionResult Index(SubPageType currentPage)
{
    // ...
    return View(currentPage);
}

It is all injected using an IServiceCollection extension method:

options.AddPolicy(profile.Key, builder =>
    {
        builder.Tag(profile.Key);
        builder.SetVaryByRouteValue(profile.Value?.VaryByRouteValueNames);
        builder.SetVaryByQuery(profile.Value.VaryByQueryKeys);
        // ...

What I need to be able to do is to evict a single cached item. The SubPageType currentPage is routed through a CMS and can have pretty much any URL depending on the site structure. Default the OutputCache use the URL as a key, I have however not found a way to invalidate items in the OutputCache using the key.

Is it possible to set a Tag dynamically? E.g. having the URL as a tag per page. Or possibly create a custom OutputCacheAttribute where this would be possible and jack that attribute up to the CacheEntry pipeline.

Any help is appreciated.

Answer 1

You can creat a custom DynamicTagCachePolicy to Override the default policy.

And in CacheRequestAsync method to add the custom tags.

    ValueTask IOutputCachePolicy.CacheRequestAsync(OutputCacheContext context,CancellationToken cancellationToken)
    {
        //...
        var route = context.HttpContext.Request.Path.ToString();
        var userId = "uid";

        var dynamicTag = $"{route}_{userId}";
        context.Tags.Add(dynamicTag);

        return ValueTask.CompletedTask;
    }