Caching partials in Umbraco 7.7

Umbraco has a nice way of implementing output caching in the views. It is exactly the same ass calling a partial, but you can say how long you want that partial to be cached and how should Umbraco understand if it should return cached data or build it again.
You could find the documentation in here.

Quick examples:

one can use CachedPartial without specifying anything else which means that you want the same partial showing every time no matter where it is.

For instance if you want to show footer or menu of your site, it is pretty easy to have them in a partial and then just call Html.CachedPartial("_menu",....) on the master page/ layout page.

  @Html.CachedPartial("_partial", Model, chachtime)//caching for everypage

On the other hand you might want to show different views for each member. An example could be a module to show username or other user specified data.

  @Html.CachedPartial("_partial", Model, chachtime,cacheByMember:true)//caching based on the member

Then there are times that you want to have your data showing differently based on different pages that they are on. For instance you want to write meta data of each page, but you don't care which user is that.

  @Html.CachedPartial("_partial", Model, chachtime,cacheByPage:true)//caching based on pages

 We can also do combination of page and members. 

  @Html.CachedPartial("_partial", Model, chachtime,cacheByPage:true,cacheByMember:true)//caching based on pages and members

But what if you want to cache your partial based on something else? What if you have some querystrings that contains some items that you want to differentiate based on that?

Lets say you have a small advertising site and for some reasons, you have your product Ids in the querystring. If you cache the page by page, it will just show everyone the first product that someone has browsed for the cache period which is not good.

Cachebymemebr is not also usable because you don't care if the person is logged in or different. You just care about the querystring that you have (productIds)

The way to do it is using contextualKeyBuilder like below: 

@Html.CachedPartial("_partial", Model, chachtime, 
contextualKeyBuilder:(o, dictionary) => 
CurrentPage.Id.ToString() + Request.QueryString.ToString())
You can specify the key based on your scenario or even pageview data.