cacheTag

In order to clear a specific cache, we first need to tag the data result, then we can call the revalidateTag function to clear any data linked to that tag so that a fresh request to the database will be made next time it is requested.

To tag the function, we use the cacheTag function. We provide this function with a list of 1 or more string values. Any of these string values can be used to revalidate the cache. Eg. in our getCategory function, we could choose to add two tags. One for categories, to clear all category data and one for category:xx, with xx being the category id. This then enables us to clear the cache for every category at once, or the cache for a specific category id. This then enables us to add a revalidateTag function in the update a specific category function to only clear the cache of that category, but also allows us to have a much wider reaching clear all the categories caches admin function for emergencies etc. The tag used can be any single string, but i personally like to use the : to break up the data as i know i wont have a : in the id fields. You could just as easily use a - or a | etc. or have no seperator at all and just have categoryxx.

So to tag the function in our example in the last section we would do:

This then adds two tags to the function. One for categories and one for category:id.

Then you would call this to clear the cache for all the categories:

And in your update category function you could call something like:

So now we can cache the data and clear the cache, next is how to choose how long the cache gets saved for in the next section.