a.rb

  model = 
    SomeActiveRecordModel

  conditions = 
    [
      # ...
    ]

  cache_key =
    md5(conditions.to_json)

  records_json =
    Rails.cache.fetch(cache_key) do
      records = query.where(conditions)
      records.map{|record| record.attributes}.to_json
    end

  records_data =
    JSON.parse(records_json)

  records_array =
    records_data.map{|attributes| model.instantiate(attributes)}