Ruby / Rails meta programing, how to define instance and class methods dynamically? - ruby-on-rails

Question

I am trying to make my life simpler inside of a large production Rails 6.0 website. I have a bunch of data that I serve from Redis as denormalized hashes, because Rails, with all the includes and associations is very very slow.
To keep things DRY, I'd like to use a Concern (or module) that can be included within ApplicationRecord that allows me to dynamically define the collection methods for the data I want to store.
This is what I have so far:
class ApplicationRecord < ActiveRecord::Base
include DenormalizableCollection
# ...
end
# The model
class News < ApplicationRecord
denormalizable_collection :most_popular
# ...
end
# The Concern
module DenormalizableCollection
extend ActiveSupport::Concern
class_methods do
def denormalizable_collection(*actions)
actions.each do |action|
# define News.most_popular
define_singleton_method "#{action}" do
collection = Redis.current.get(send("#{action}_key"))
return [] unless collection.present?
JSON.parse(collection).map { |h| DenormalizedHash.new(h) }
end
# define News.set_most_popular
define_singleton_method "set_#{action}" do
Redis.current.set(send("#{action}_key"), send("#{action}_data").to_json)
end
# define News.most_popular_data, which is a method that returns an array of hashes
define_singleton_method "#{action}_data" do
raise NotImplementedError, "#{action}_data is required"
end
# define News.most_popular_key, the index key to use inside of redis
define_singleton_method "#{action}_key" do
"#{name.underscore}_#{action}".to_sym
end
end
end
end
end
This works, but I doesn't seems right because I cannot also define instance methods, or ActiveRecord after_commit callbacks to update the collection inside of Redis.
I'd like to add something like the following to it:
after_commit :set_#{action}
after_destroy :set_#{action}
But obviously these callbacks require an instance method, and after_commit :"self.class.set_most_popular" causes an error to be thrown. So I had wanted to add an instance method like the following:
class News
# ...
def reset_most_popular
self.class.send("set_most_popular")
end
end
I have been reading as many articles as I can and going through the Rails source to see what I'm missing - as I know I'm defo missing something!

Answer 1

The key here is to use class_eval to open up the class you are calling denormalizable_collection on.
A simplified example is:
class Foo
def self.make_method(name)
class_eval do |klass|
klass.define_singleton_method(name) do
name
end
end
end
make_method(:hello)
end
irb(main):043:0> Foo.hello
=> :hello
module DenormalizableCollection
def self.included(base)
base.extend ClassMethods
end
module ClassMethods
def denormalizable_collection(*actions)
actions.each do |action|
generate_denormalized_methods(action)
generate_instance_methods(action)
generate_callbacks(action)
end
end
private
def generate_denormalized_methods(action)
self.class_eval do |klass|
# you should consider if these should be instance methods instead.
# define News.most_popular
define_singleton_method "#{action}" do
collection = Redis.current.get(send("#{action}_key"))
return [] unless collection.present?
JSON.parse(collection).map { |h| DenormalizedHash.new(h) }
end
# define News.most_popular
# define News.set_most_popular
define_singleton_method "set_#{action}" do
Redis.current.set(send("#{action}_key"), send("#{action}_data").to_json)
end
# define News.most_popular_data, which is a method that returns an array of hashes
define_singleton_method "#{action}_data" do
raise NotImplementedError, "#{action}_data is required"
end
# define News.most_popular_key, the index key to use inside of redis
define_singleton_method "#{action}_key" do
"#{name.underscore}_#{action}".to_sym
end
end
end
def generate_callbacks(action)
self.class_eval do
# Since callbacks call instance methods you have to pass a
# block if you want to call a class method instead
after_commit -> { self.class.send("set_#{action}") }
after_destroy -> { self.class.send("set_#{action}") }
end
end
def generate_instance_methods(action)
class_eval do
define_method :a_test_method do
# ...
end
end
end
end
end
Note here that I'm not using ActiveSupport::Concern. Its not that I don't like it. But in this case it adds an additional level of metaprogramming thats enough to make my head explode.

Answer 2

Have you tried something like:
class_methods do
def denormalizable_collection(*actions)
actions.each do |action|
public_send(:after_commit, "send_#{action}")
...
end
end
end