Rails.cache.fetch does not work for array of json

I am trying to cache server API response using Rail.cache.fetch feature but it seems like just always 'nil' instead cached data. Method below runs one time, then always fails with 'access to nil class' kind error when I am trying to go through @my_api_data_ variable

def index
  api_statuses_

end
def api_statuses_
  Rails.cache.fetch('api_repsonse_m_', expires_in: 3.minute) do


      @mypairs_ = ['ticker1','ticker2', 'ticker3', 'ticker4', 'ticker5', 'ticker6', 'ticker7', 'ticker8', 'ticker9', 'ticker10']

      @my_api_data_ = []
      @my_api_data_poplr = []
      url = 'https://myserver.com/ticker/'

      @mypairs_.each do |item_|
        uri = URI(url + item_)
        response = Net::HTTP.get(uri)
        begin
          #response is like this {"status":"valu1","time":"valu2","data":"valu3"}
          myresult = JSON.parse(response)
        rescue JSON::ParserError

        end
        #Rails.logger.info myresult
        @my_api_data_.push(myresult);
      end

  end
end

I hope maybe someone knows why it goes bad each time

I tried to add line "@my_api_data_" right before the end of cache block. This is the same error I got on original circumstances:

I, [2018-01-13T19:29:14.384766 #5716]  INFO -- : Processing by Private::MydataController#index as HTML
I, [2018-01-13T19:29:14.403774 #5716]  INFO -- :   Rendered private/mydata/index.html.slim within layouts/mydatalayout_ (0.7ms)
I, [2018-01-13T19:29:14.403919 #5716]  INFO -- : Completed 500 Internal Server Error in 19ms
F, [2018-01-13T19:29:14.405077 #5716] FATAL -- : 
ActionView::Template::Error (undefined method `each' for nil:NilClass):
    37:         .row
    38:           /! Top head coin-boxes
    39:           .market-top-coin-boxes
    40:             - @my_api_data_.each do |pair_data|

It seems that the problem here is that you have to return @my_api_data_ at the end of the block. Let check the code below:

def api_statuses_
  Rails.cache.fetch('api_repsonse_m_', expires_in: 3.minute) do
    @mypairs_ = ['ticker1','ticker2', 'ticker3', 'ticker4', 'ticker5', 'ticker6', 'ticker7', 'ticker8', 'ticker9', 'ticker10']

    @my_api_data_ = []
    @my_api_data_poplr = []
    url = 'https://myserver.com/ticker/'

    @mypairs_.each do |item_|
      uri = URI(url + item_)
      response = Net::HTTP.get(uri)
      begin
        #response is like this {"status":"valu1","time":"valu2","data":"valu3"}
        myresult = JSON.parse(response)
      rescue JSON::ParserError
      end
      #Rails.logger.info myresult
      @my_api_data_.push(myresult);
    end
    @my_api_data
  end
end

Note that the first time that you call the api_statuses_ method all the blocked will be executed, and the return value will be written to the cache under the api_repsonse_m_ key. So, the next time that you call api_statuses_, and if the time in expires_in has not expired, it will return the value save in the cache and the block will not be executed.

Also, could you show us where and how are you using this method? Showing the code and the error log could be great to understand the problem.

Updated: It seems that you are not using correctly this. You should call the api_statuses_ method in the index method under the MydataController controller, and save the return value to a variable that will be use in your view.

For instance:

module Private
  class MydataController
    def index 
      @api_statuses = api_statuses_
    end
  end
end

Then, in your view:

.row
  .market-top-coin-boxes
    - @api_statuses.each do |pair_data|