Ruby on Rails instance variable caching based on parameters

Question

I am storing users miscellaneous data in user_data table and when I am retrieving that data with the association I defined and then I am actually caching it using Ruby instance Variable caching like this.

def user_data(user_id)
  @user_data || = User.find(user_id).data 
end

but instance variable @user_data will be allocated value only first time when it's nil and once it hold data for a user lets say for user_id equal to 1,and when I am passing user_id 2 in this method it's returning data for user_id 1 , because it will not allocate new value to it so my question is how can I cache it's value based on parameters of function.

Aleksey Shein · Accepted Answer · 2015-10-27 10:51:24Z

11

Take a look at the Caching with Rails guide. Rails can cache data on multiple levels from full page caching to fragment caching, I strongly advise you to read all this page so you can make a perceived choice.

For the low-level caching you can do this:

@user_data = Rails.cache.fetch("user_#{user_id}", expires_in: 1.hour) do
  User.find(user_id).data
end

By default Rails stores cache on disk, but you can setup for memcache, memory store, and etc.

answered Oct 27, 2015 at 10:51

Aleksey Shein

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2 Comments

kaspernj Over a year ago

This is how you would implement it using the Rails caching. This is not to be confused with instance variable caching though, which the question is about. Upvoted :-)

Joshua Pinter Aug 21 at 12:56

FYI, use cache_key or cache_key_with_version instead of "user_#{user_id}".

kaspernj · Accepted Answer · 2015-10-27 11:19:17Z

4

You can use a hash for a key-based intance-variable-cache. I think that does what you want.

def user_data(user_id)
  @user_data ||= {}
  @user_data[user_id.to_i] || = User.find(user_id).data 
end

answered Oct 27, 2015 at 11:19

kaspernj

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1 Comment

Chris Betti Over a year ago

This approach causes @user_data to grow without bound. Keep your total cache-able dataset size in mind if considering something like this.

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