How do I use a Rails cache to store Nokogiri objects?

Question

I'm using Rails 5 to use a Rails cache to store Nokogiri objects.

I created this in config/initializers/cache.rb:

$cache = ActiveSupport::Cache::MemoryStore.new

and I wanted to store documents like:

$cache.fetch(url) {
  result = get_content(url, headers, follow_redirects)
}

but I'm getting this error:

Error during processing: (TypeError) no _dump_data is defined for class Nokogiri::HTML::Document
/Users/davea/.rvm/gems/ruby-2.4.0/gems/activesupport-5.0.2/lib/active_support/cache.rb:671:in `dump'
/Users/davea/.rvm/gems/ruby-2.4.0/gems/activesupport-5.0.2/lib/active_support/cache.rb:671:in `dup_value!'
/Users/davea/.rvm/gems/ruby-2.4.0/gems/activesupport-5.0.2/lib/active_support/cache/memory_store.rb:128:in `write_entry'
/Users/davea/.rvm/gems/ruby-2.4.0/gems/activesupport-5.0.2/lib/active_support/cache.rb:398:in `block in write'
/Users/davea/.rvm/gems/ruby-2.4.0/gems/activesupport-5.0.2/lib/active_support/cache.rb:562:in `block in instrument'
/Users/davea/.rvm/gems/ruby-2.4.0/gems/activesupport-5.0.2/lib/active_support/notifications.rb:166:in `instrument'
/Users/davea/.rvm/gems/ruby-2.4.0/gems/activesupport-5.0.2/lib/active_support/cache.rb:562:in `instrument'
/Users/davea/.rvm/gems/ruby-2.4.0/gems/activesupport-5.0.2/lib/active_support/cache.rb:396:in `write'
/Users/davea/.rvm/gems/ruby-2.4.0/gems/activesupport-5.0.2/lib/active_support/cache.rb:596:in `save_block_result_to_cache'
/Users/davea/.rvm/gems/ruby-2.4.0/gems/activesupport-5.0.2/lib/active_support/cache.rb:300:in `fetch'
/Users/davea/Documents/workspace/myproject/app/helpers/webpage_helper.rb:116:in `get_cached_content'
/Users/davea/Documents/workspace/myproject/app/helpers/webpage_helper.rb:73:in `get_url'
/Users/davea/Documents/workspace/myproject/app/services/abstract_my_object_finder_service.rb:29:in `process_data'
/Users/davea/Documents/workspace/myproject/app/services/run_crawlers_service.rb:26:in `block (2 levels) in run_all_crawlers'
/Users/davea/.rvm/gems/ruby-2.4.0/gems/concurrent-ruby-1.0.5/lib/concurrent/executor/ruby_thread_pool_executor.rb:348:in `run_task'
/Users/davea/.rvm/gems/ruby-2.4.0/gems/concurrent-ruby-1.0.5/lib/concurrent/executor/ruby_thread_pool_executor.rb:337:in `block (3 levels) in create_worker'
/Users/davea/.rvm/gems/ruby-2.4.0/gems/concurrent-ruby-1.0.5/lib/concurrent/executor/ruby_thread_pool_executor.rb:320:in `loop'
/Users/davea/.rvm/gems/ruby-2.4.0/gems/concurrent-ruby-1.0.5/lib/concurrent/executor/ruby_thread_pool_executor.rb:320:in `block (2 levels) in create_worker'
/Users/davea/.rvm/gems/ruby-2.4.0/gems/concurrent-ruby-1.0.5/lib/concurrent/executor/ruby_thread_pool_executor.rb:319:in `catch'
/Users/davea/.rvm/gems/ruby-2.4.0/gems/concurrent-ruby-1.0.5/lib/concurrent/executor/ruby_thread_pool_executor.rb:319:in `block in create_worker'

What do I need to do in order to be able to store these objects in a cache?

Answer 1

Store the xml as string, not the object and parse them once you get them out of the cache.

Edit: response to comment

Cache this instead

nokogiri_object.to_xml

Edit2: response to comment. Something along this lines. You will need to post more code if you want more specific help.

nokogiri_object = Nokogiri::XML(cache.fetch('xml_doc'))

Edit3: Response to 'Thanks but what is the code for "Store serialized object in cache"? I thought the body of the "$cache.fetch(url) {" would take care of storing and then retrieving things?'

cache.write('url', xml_or_serialized_nokogiri_string)