Add caching without changing any call sites

Instead of building separate cached code paths or providing new API such as Product.fetch, RedisMemo takes advantage of metaprogramming in Ruby and adds caching to existing code paths as annotation:

class Post < ApplicationRecord
  extend RedisMemo::MemoizeMethod
  def author_display_name
    author.display_name
  end
  memoize_method :author_display_name do |post|
    depends_on Post.where(id: post.id)
    depends_on User.where(id: post.author_id)
  end
end

Here are some of the motivations:

• Caching should be the default behavior, rather than a conscious choice each developer has to make every time; they might not even be aware of the existence of the cached code path.
• Cached and uncached code paths can diverge over time. Switching to the cached ones may require changing a ton of files; it’s not always possible to change all the call sites, since some of them could be used in some gem code.
• Separate code paths such as Product.fetch have other usability and compatibility issues with ActiveRecord. Learn more about those issues here.

Footnotes

1. We’re aware of Shopify/identity_cache, a gem that also provides query caching with automatic cache invalidation. It documented the motivation for providing separate cached query code paths in its caveats. With RedisMemo, caching is still a deliberate decision: there are models and computations that would not benefit from caching. When caching does make sense, RedisMemo makes caching easy and robust.