Ruby on rails 如果值为nil，如何告诉Rails inmemory cache不要创建条目？

我使用的是Rails 5。我希望使用Rails内存存储缓存来缓存数据，但是，如果数据的值为零，我不希望缓存此类数据。我该怎么做？我认为我可以扩展Rails缓存并编写自己的方法，所以我找到了下面的代码

module ActiveSupport
 module Cache
    class Store
      def fetch_no_nil(name, options = nil)
        if block_given?
          options = merged_options(options)
          key = namespaced_key(name, options)

          cached_entry = find_cached_entry(key, name, options) unless options[:force]
          entry = handle_expired_entry(cached_entry, key, options)

          if entry
            get_entry_value(entry, name, options)
          else
            save_block_result_to_cache_if_not_nil(name, options) { |_name| yield _name }
          end
        else
          read(name, options)
        end
      end
      private
      def save_block_result_to_cache_if_not_nil(name, options)
        result = instrument(:generate, name, options) do |payload|
          yield(name)
        end
        write(name, result, options) unless result.nil?
        result
      end
    end
  end
end

然而，这似乎对Raisl 5不起作用。我在调用“fetch\u no\u nil”方法时出现以下错误

Please use `normalize_key` which will return a fully resolved key.
 (called from fetch_no_nil at /Users/davea/Documents/workspace/myproject/config/initializers/enhanced_cache.rb:7)
NoMethodError: undefined method `find_cached_entry' for #<ActiveSupport::Cache::MemoryStore:0x007fa6b92ae088>
    from /Users/davea/Documents/workspace/myproject/config/initializers/enhanced_cache.rb:9:in `fetch_no_nil'
    from /Users/davea/Documents/workspace/myproject/app/helpers/webpage_helper.rb:116:in `get_cached_content'
    from /Users/davea/Documents/workspace/myproject/app/helpers/webpage_helper.rb:73:in `get_url'
    from (irb):1
    from /Users/davea/.rvm/gems/ruby-2.4.0/gems/railties-5.0.2/lib/rails/commands/console.rb:65:in `start'
    from /Users/davea/.rvm/gems/ruby-2.4.0/gems/railties-5.0.2/lib/rails/commands/console_helper.rb:9:in `start'
    from /Users/davea/.rvm/gems/ruby-2.4.0/gems/railties-5.0.2/lib/rails/commands/commands_tasks.rb:78:in `console'
    from /Users/davea/.rvm/gems/ruby-2.4.0/gems/railties-5.0.2/lib/rails/commands/commands_tasks.rb:49:in `run_command!'
    from /Users/davea/.rvm/gems/ruby-2.4.0/gems/railties-5.0.2/lib/rails/commands.rb:18:in `<top (required)>'
    from bin/rails:4:in `require'
    from bin/rails:4:in `<main>'

请使用“normalize_key”，它将返回完全解析的密钥。
（在/Users/davea/Documents/workspace/myproject/config/initializers/enhanced_cache.rb:7处从fetch_no_nil调用）
NoMethodError:未定义的方法“查找缓存项”#
来自/Users/davea/Documents/workspace/myproject/config/initializers/enhanced_cache.rb:9:in'fetch_no_nil'
from/Users/davea/Documents/workspace/myproject/app/helpers/webpage\u helper.rb:116:in'get\u cached\u content'
from/Users/davea/Documents/workspace/myproject/app/helpers/webpage\u helper.rb:73:in'get\u url'
来自（irb）：1
from/Users/davea/.rvm/gems/ruby-2.4.0/gems/railties-5.0.2/lib/rails/commands/console.rb:65:in'start'
来自/Users/davea/.rvm/gems/ruby-2.4.0/gems/railties-5.0.2/lib/rails/commands/console\u helper.rb:9:in“start”
from/Users/davea/.rvm/gems/ruby-2.4.0/gems/railties-5.0.2/lib/rails/commands/commands\u tasks.rb:78:在“控制台”中
来自/Users/davea/.rvm/gems/ruby-2.4.0/gems/railties-5.0.2/lib/rails/commands/commands\u tasks.rb:49:in“run\u command！”
来自/Users/davea/.rvm/gems/ruby-2.4.0/gems/railties-5.0.2/lib/rails/commands.rb:18:in`'
从箱子/轨道：4:in“require”
从箱子/轨道：4:in`'

---

如果值为零，是否有其他方法可以指示Rails缓存不创建条目？

不要使用monkeypatch

ActiveSupport:：cache

。只需编写一个包装器方法：

def self.cache_unless_nil(key, value)
  Rails.cache.fetch(key) { value } unless value.nil?
end

然后通过调用包装器缓存对象：

cache_unless_nil("foo", "bar")
Rails.cache.fetch("foo")
#=> "bar"
cache_unless_nil("baz", nil)
Rails.cache.fetch("baz")
#=> nil