Excerpt
I'm implementing some caching by using the nifty Rails.cache.fetch. However, in one particular instance, sometimes I encounter an exception:
```plain text
TypeError in EmloController#index
Emlo can't be referred to
app/controllers/emlo_controller.rb:320:in `get_employees'
app/controllers/emlo_controller.rb:356:in `prepare_json_response'
app/controllers/emlo_controller.rb:23:in `block (2 levels) in index'
app/controllers/emlo_controller.rb:15:in `index'
```
It seems the fetch will always explode (with the above) on the first try, and then work fine as long as the fetch is within the expiration. I know I'm missing something, so a fresh pair of eyes would be nice.
Here's the method which invokes the cache fetch:
```plain text
def get_employees
# This is for a AJAX refresh loop, so a 5-second cache actually helps quite a bit
Rails.cache.fetch('emlo_all', :expires_in => 5.seconds, :race_condition_ttl => 1) do
conditions = (params[:id]) ? {:user_id => params[:id]} : nil
selections = [
'employee_locations.id AS emlo_id',
'employee_locations.status_id',
'employee_locations.notes',
'employee_locations.until',
'employee_locations.updated_at',
'employee_locations.user_id',
'location_states.id AS state_id',
'location_states.title AS status_string',
'location_states.font_color',
'location_states.bg_color',
'users.displayname',
'users.email',
'users.mobile',
'users.department',
'users.extension',
'users.guid',
'users.dn'
].join(', ')
Emlo.all(
:select => selections,
:joins => 'LEFT JOIN users ON employee_locations.user_id=users.id LEFT JOIN location_states ON employee_locations.status_id=location_states.id',
:conditions => conditions,
:order => 'users.displayname ASC'
)
end
end
```
This problem arises in development mode when config.action_controller.perform_caching = true AND config.cache_classes = false -- it seems ActiveRecord objects cannot be stored with Rails.cache.
But if you need to enable config.action_controller.perform_caching in development mode for testing caching, then you must also enable config.cache_classes.
This would be temporary, though, because then you'd have to restart
the development server after changing classes or files in the asset
pipeline.
With caching disabled, I would use Rails.cache.write(some_name, some_value) if Rails.env.production? to prevent caching from blowing up in development. Rails.cache.read() doesn't seem to be affected.