Manually Clear Fragment Cache in Rails

Question

I'm using Memcached with Heroku for a Rails 3.1 app. I had a bug and the wrong things are showing - the parameters were incorrect for the cache.

I had this:

<% cache("foo_header_cache_#{@user.id}") do %>

I removed the fragment caching and pushed to Heroku and the bad data went away.

And then I changed it to:

<% cache("foo_header_cache_#{@foo.id}") do %>

However, when I corrected the parameters, from @user to @foo, the old [incorrect] cached version showed again (instead of refreshing with the correct data).

How can I manually expire this, or otherwise get rid of this bad data that is showing?

score 44 · Accepted Answer · answered May 05 '12 at 07:13

44

I ended up manually clearing the entire cache by going into the rails console and using the command:

Rails.cache.clear

answered May 05 '12 at 07:13

yellowreign

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John Kloian's answer allows you to expire a single fragment. If you have a site that gets a fair amount of traffic and relies on caching, expiring everything could result in very slow page loads or timeout errors as the cache is warmed. – Patrick Brinich-Langlois Feb 25 '17 at 01:21

score 30 · Answer 2 · answered Sep 01 '14 at 16:08

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From the rails console:

Rails.cache.delete 'FRAGMENT-NAME'

answered Sep 01 '14 at 16:08

John Kloian

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This is now the correct answer. The accepted one is using a shotgun to kill a fly. – Chuck Callebs Mar 17 '16 at 18:26
That's what works for me for expiring a fragment cache in Rails 4.2: `Rails.cache.delete(['views', 'FRAGMENT-NAME'])` – rorofromfrance Dec 22 '21 at 10:42

score 21 · Answer 3 · edited May 23 '17 at 12:10

21

Here you are:

<% ActionController::Base.new.expire_fragment("foo_header_cache_#{@user.id}") %>

Reference:
- How to call expire_fragment from Rails Observer/Model?

edited May 23 '17 at 12:10

Community

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answered Mar 16 '13 at 10:00

Adit Saxena

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Mark Swardstrom · Answer 4 · 2016-09-01T22:09:32.627

From the console:

You can run this (ie. if you know the id is '1')

ActionController::Base.new.expire_fragment("foo_header_cache_1")

To use Rails.cache.delete you need to know the fragment name. In your case, it would be

Rails.cache.delete("views/foo_header_cache_1") # Just add 'views/' to the front of the string

If you have an array-based cache key using objects, such as:

cache([:foo_header_cache, @user])

Then you can get the fragment name like so

ActionController::Base.new.fragment_cache_key([:foo_header_cache, @user])

The name includes the id and updated_at time from any objects (to the yyyymmddhhmmss). It would be something like "views/foo_header_cache/users/1-20160901021000"

Or simply clear it using the array.

ActionController::Base.new.expire_fragment([:foo_header_cache, @user])

I think this is the most accurate answer. After many uses I figured this is a bit cleaner to use instead of calling the ActionController module: `Rails.cache.clear(['views', :foo_header_cache, @user])` (works in Rails 4.2 at least) — rorofromfrance, Dec 22 '21 at 10:39

Manually Clear Fragment Cache in Rails

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