Rails.cache.fetch inserting extra values

Question

We have a page which shows the top groups for our application. The calculation of the leader board is expensive so we cache the results for an hour as follows: ``` @groupboard = Rails.cache.fetch("top_groups", :expires_in => 1.hour) do Group.top_groups end ``` This is giving an error after the cache has been written the first time. Poking around in the console I see that Group.top_groups returns an array of items that look as follows: ``` [#, 3887] ``` When I look at the result returned from the cache it looks as follows: ``` [#, :@new_record_before_save], false, 3887] ``` Does anyone know what would be causing @new_record_before_save and the 'false' value to be inserted into all the entries for this object in the cache? We are using Dalli, Memcached 1.4.9, Rails 3.2.4, Ruby 1.9.2

Accepted Answer

There is a bug of Rails cache on AR object which has associated object. Try following:

```
@groupboard = Rails.cache.fetch("top_groups", :expires_in => 1.hour) do  
  Group.top_groups.map(&:reload)
end
```

see more on https://github.com/mperham/dalli/issues/250

Rails.cache.fetch inserting extra values

Solution

Problem