Rails Cached Method

Simple way to cache results of methods. Using Rails.cache inside with default expiration time of 1 minute.

Usage

To get a value and cache it just write a code like:

User.cached.admins # get list of admins and automatically put them in cache with 1 minute TTL
post.cached.comments.last # get last comment from the post and cache it
User.cached.where(role: :moderator).count # cache moderators count
Project.cached.first.some_heavey_method # cache result of some_heavey_method for first Project (if first is Project.first)

So basically just call method cached on any object. It will wrap and cache every result from the next method call. So every result from method chain is cached.

For example:

post.cached.comments.first # A
post.cached.comments.last  # B

Here post.cached.comments will return same collection.

You don't need to specify a key, because it's dynamically set based on object, arguments, etc.

Options:

cached(key: nil, expires_in: 1.minute, recache: false)

key - you can set your key. expires_in - TTL of cached object. recache - should be key deleted and cached again.

Tips & Tricks

1. use if page.present? to check if value is really present. Because every value is wrapped in a class if statement can work incorrectly

    page = Page.cached.find_by(identifier: identifier)
    return page if page # change to return page if page.present?
    page = Page.new(identifier: identifier, title: identifier)
    page.save(validate: false)
    page

2. Rails.cache.clear in specs before(:suite) or concrete spec

How it works

After you call .cached it will generate a cache key and store value in Rails.cache. Value is class which is wrapps original value and allow you to call methods on the value using method_missing. Every result is cached again and again. So on every method call in methods chain every result will be stored in Rails.cache.

To get original value you can call .__value__.

Some pieces of code to show you how it works:

    def cached(key: nil, expires_in: 1.minute, recache: false)
      CachedProxy.new(
        self,
        key: key,
        expires_in: expires_in,
        recache: recache
      )
    end
# ---------------------------------------------------------------
    class CachedProxy

    Object.methods.each do |e|
      delegate e, to: :@__object__
    end
    
    def method_missing(*args)
      key = ___compose_key__(args)
      if @__recache__
        Rails.cache.delete(key)
      end
      Rails.cache.fetch(key, expires_in: @__expires_in__) do
        CachedProxy.new(
          @__object__.send(*args),
          expires_in: @__expires_in__,
          recache: @__recache__,
          parent_key: key,
        )
      end
    end    
    private
    def ___compose_key__(args)
      result = [@__parent_key__, @__key__]
      result += if @__object__.respond_to?(:to_global_id)
        [@__object__.to_global_id]
      elsif @__object__.is_a?(ActiveRecord::Relation)
        [@__object__.class]
      else
        [@__object__]
      end
      result += args[0..1]
      result.compact.map(&:to_s).join('.').dasherize
    end

Installation

Add this line to your application's Gemfile:

gem 'rails_cached_method'

And then execute:

$ bundle

Or install it yourself as:

$ gem install rails_cached_method

TODO

• think if rails dependency could be replaced with something more lightweight

Contributing

Contribution directions go here.

License

The gem is available as open source under the terms of the MIT License.