How to cache content per user?

Question

Is there a way to cache content with the (% cache %} tag on a per-user base?

If user A is logged in, his content gets cached. User B logs in, but his content should not interfere with that of User A.

Answer 1

In the upcoming Craft 2.2 release, we've added a using key parameter to the {% cache %} tag for for situations like this.

So you'd be able to do something like this for per user caching:

{% cache using key "myImportantUserCache" ~ currentUser.id %}

Answer 2

You could add user dependent content in between your cache tags to make the cache invalidate itself every time the page is requested by a new user. This probably doesn't help you much (but depends on the use case):

{% cache %}
    <div class="hidden">{{ currentUser.id }}</div>
{% endcache %}

.

Another idea is to have user specific URLs. That'd work because each URL gets its own cache entry in the DB (see Brad's comment¹).

For the pages in question, add user specific info to the URL in your links:
<a href="/{{ currentUser.id }}/blog/{{ entry.slug }}">{{ entry.title }}</a>

and then use dynamic routes to make them work:
URI format:<*>/blog/<*> → Template: blog/_entry.html

.

^{1: "The cache, by default will cache it's contents on a per URL and per locale basis."}