Issues with separate cached ActiveRecord code paths

Suppose we are adding separate cached code paths for some ActiveRecord methods:

• teacher.sites -> teacher.cached_sites
• Site.find -> Site.cached_find
• Site.where -> Site.cached_where

Lazy Loading

Many querying methods return an ActiveRecord::Relation. There’s no data fetching until it’s absolutely necessary. If we simply added cached methods such as teacher.cached_sites and Site.cached_where, we would not be able to implement lazy loading.

Association Preloading

A common technique to avoid N+1 query:

teachers = Teacher.preload(:site).where(...)

teachers.map(&:site) # no additional queries!

Simply adding a cached_where would bypass this optimization.

Association Scope

With ActiveRecord, one could have associations with a scope as follows:

belongs_to :local_site, -> { where(location: ...) }

Simply adding a cached_local_site would not be ideal:

• It interferes with the association cache
• It does not support lazy loading

inverse_of

One could use inverse_of to retrieve the same Ruby object instance using different querying methods (example). Simply adding a cached code path would bypass this functionality.

# app/models/author.rb
class Author < ActiveRecord::Base
  has_many :posts, inverse_of: :author
end

Not always possible to change all the call sites

External gem code could use any ActiveRecord query methods. It’s not practical to patch all the gems to use the cached ActiveRecord code path (for example, ActiveJob serializes and deserializes job arguments).