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Presentation Title
Author
Demystifying some of the
magic behind Rails
@Ridhwana_K
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Cape Town
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π©π»Lead Software Engineer,
π Technical Writer,
&
π₯ Community Builder
β¦.but most importantly,
A Cat Mom.
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Zeus Zoey
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Technical Writer for Rails Guides
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Rails
Documentation
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Rails Documentation Team
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2. β Writing & Team Review
1. π» Audit
3. π PR & Community Review
Three Step Process:
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What Can You Expect?
1. Navigating the Source Code: Explore strategies to
trace through the Rails
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What Can You Expect?
1. Navigating the Source Code: Explore strategies to
trace through the Rails
2. Examples: Tracing through three different modules in
Rails
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What Can You Expect?
1. Navigating the Source Code: Explore strategies to
trace through the Rails
2. Examples: Tracing through three different modules in
Rails
3. Metaprogramming Evaluation: Benefits & Drawbacks
of metaprogramming within the Rails source
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What Can You Expect?
1. Navigating the Source Code: Explore strategies to
trace through the Rails
2. Examples: Tracing through three different modules in
Rails
3. Metaprogramming Evaluation: Benefits & Drawbacks
of metaprogramming within the Rails source
4. Using these Patterns in the Wild: Apply these
techniques to different use cases
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Navigating the
Source Code
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Rails API docs
&
Ruby on Rails
Guides
https://guides.rubyonrails.org/
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Rails API docs
&
https://api.rubyonrails.org/
Ruby on Rails
API
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Rails API docs
&
https://github.com/rails/rails/blob/main/activemodel/README.rdoc
README Files
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source_location
User.method(:find_by).source_location
["/Users/username/.rbenv/versions/
3.1.4/lib/ruby/gems/3.1.0/gems/
activerecord-6.1.7.3/lib/active_record/
relation/finder_methods.rb", 271]
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Patterns
&
Conventions
236 results - 109 files
actioncable/lib/action_cable/connection/tagged_logger_proxy.rb:
35 %i( debug info warn error fatal unknown ).each do |severity|
36: define_method(severity) do |message = nil, &block|
37 log severity, message, &block
actionpack/lib/abstract_controller/callbacks.rb:
230 [:before, :after, :around].each do |callback|
231: define_method "#{callback}_action" do |*names, &blk|
232 _insert_callbacks(names, blk) do |name, options|
236
237: define_method "prepend_#{callback}_action" do |*names, &blk|
238 _insert_callbacks(names, blk) do |name, options|
244 # the allowed parameters.
245: define_method "skip_#{callback}_action" do |*names|
246 _insert_callbacks(names) do |name, options|
actionpack/lib/abstract_controller/railties/routes_helpers.rb:
11 Module.new do
12: define_method(:inherited) do |klass|
13 super(klass)
actionpack/lib/action_controller/metal/flash.rb:
37
38: define_method(type) do
39 request.flash[type]
actionpack/lib/action_controller/metal/renderers.rb:
75 def self.add(key, &block)
76: define_method(_render_with_renderer_method_name(key), &block)
77 RENDERERS << key.to_sym
actionpack/lib/action_dispatch/http/content_security_policy.rb:
187 DIRECTIVES.each do |name, directive|
188: define_method(name) do |*sources|
189 if sources.first
actionpack/lib/action_dispatch/http/permissions_policy.rb:
122 DIRECTIVES.each do |name, directive|
123: define_method(name) do |*sources|
124 if sources.first
actionpack/lib/action_dispatch/routing/mapper.rb:
710
711: define_method :find_script_name do |options|
712 if options.key?(:script_name) && options[:script_name].present?
actionpack/lib/action_dispatch/routing/route_set.rb:
335 def define_url_helper(mod, name, helper, url_strategy)
336: mod.define_method(name) do |*args|
337 last = args.last
517 MountedHelpers.class_eval do
518: define_method "_#{name}" do
519 RoutesProxy.new(routes, _routes_context, helpers, script_namer)
616 # extra conveniences for working with @_routes.
617: define_method(:_routes) { @_routes || routes }
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Code Editor
&
Debugger
EDITOR="code"
bundle open activerecord
EDITOR="code"
bundle open
β
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Testing Suite
class Pirate < ActiveRecord::Base
belongs_to :parrot, validate: true
has_one :ship
has_many :birds
end
class TestAutosaveAssociationValidationMethodsGeneration
< ActiveRecord::TestCase
def setup
super
@pirate = Pirate.new
end
test "should generate validation methods for has_many
associations" do
assert_respond_to
@pirate, :validate_associated_records_for_birds
end
test "should generate validation methods for has_one
associations with :validate => true" do
assert_respond_to
@pirate, :validate_associated_records_for_ship
end
test "should generate validation methods for
belongs_to associations with :validate => true" do
assert_respond_to
@pirate, :validate_associated_records_for_parrot
end
end
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Testing Suite
class Pirate < ActiveRecord::Base
belongs_to :parrot, validate: true
has_one :ship
has_many :birds
end
class TestAutosaveAssociationValidationMethodsGeneration
< ActiveRecord::TestCase
def setup
super
@pirate = Pirate.new
end
test "should generate validation methods for has_many
associations" do
assert_respond_to
@pirate, :validate_associated_records_for_birds
end
test "should generate validation methods for has_one
associations with :validate => true" do
assert_respond_to
@pirate, :validate_associated_records_for_ship
end
test "should generate validation methods for
belongs_to associations with :validate => true" do
assert_respond_to
@pirate, :validate_associated_records_for_parrot
end
end
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Github Copilot
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What is Metaprogramming?
Metaprogramming allows a
program to write or modify
its own code.
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Examples
of
Rails Patterns
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Example 1:
MIME types in a Controller Action
AbstractController::Collector
actionpack/lib/abstract_controller/collector.rb
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What does this module do?
class ArticlesController <
ApplicationController
def show
@article = Article.find(params[:id])
respond_to do |format|
format.html # renders show.html.erb
format.json { render json: @article }
end
end
end
GET /articles/1.json
Accept: application/json
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Example Code
module AbstractController
module Collector
def self.generate_method_for_mime(mime)
sym = mime.is_a?(Symbol) ? mime : mime.to_sym
class_eval <<-RUBY, __FILE__, __LINE__ + 1
def #{sym}(...)
custom(Mime[:#{sym}], ...)
end
RUBY
end
Mime::SET.each do |mime|
generate_method_for_mime(mime)
end
Mime::Type.register_callback do |mime|
generate_method_for_mime(mime) unless instance_methods.include?(mime.to_sym)
end
private
def method_missing(symbol, ...)
unless mime_constant = Mime[symbol]
raise NoMethodError, "To respond to a custom format, register it as a MIME type first: " \
"https://guides.rubyonrails.org/action_controller_overview.html#restful-downloads. " \
"If you meant to respond to a variant like :tablet or :phone, not a custom format, " \
"be sure to nest your variant response within a format response: " \
"format.html { |html| html.tablet { ... } }"
end
if Mime::SET.include?(mime_constant)
AbstractController::Collector.generate_method_for_mime(mime_constant)
public_send(symbol, ...)
else
super
end
end
end
end
generate_method_for_mime
method_missing
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module AbstractController
module Collector
def self.generate_method_for_mime(mime)
...
end
...
private
def method_missing(symbol, ...)
unless mime_constant = Mime[symbol]
raise NoMethodError, "To respond to a custom format, ..."
end
if Mime::SET.include?(mime_constant)
AbstractController::Collector.generate_method_for_mime(mime_constant)
public_send(symbol, ...)
else
super
end
end
end
end
GET /articles/1.json
Accept: application/json
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module AbstractController
module Collector
def self.generate_method_for_mime(mime)
...
end
...
private
def method_missing(symbol, ...)
unless mime_constant = Mime[symbol]
raise NoMethodError, "To respond to a custom format, ..."
end
if Mime::SET.include?(mime_constant)
AbstractController::Collector.generate_method_for_mime(mime_constant)
public_send(symbol, ...)
else
super
end
end
end
end
GET /articles/1.json
Accept: application/json
def json
...
end
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module AbstractController
module Collector
def self.generate_method_for_mime(mime)
...
end
...
private
def method_missing(symbol, ...)
unless mime_constant = Mime[symbol]
raise NoMethodError, "To respond to a custom format, ..."
end
if Mime::SET.include?(mime_constant)
AbstractController::Collector.generate_method_for_mime(mime_constant)
public_send(symbol, ...)
else
super
end
end
end
end
:json
GET /articles/1.json
Accept: application/json
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module AbstractController
module Collector
def self.generate_method_for_mime(mime)
...
end
...
private
def method_missing(symbol, ...)
unless mime_constant = Mime[symbol]
raise NoMethodError, "To respond to a custom format, ..."
end
if Mime::SET.include?(mime_constant)
AbstractController::Collector.generate_method_for_mime(mime_constant)
public_send(symbol, ...)
else
super
end
end
end
end
:json
GET /articles/1.json
Accept: application/json
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module AbstractController
module Collector
def self.generate_method_for_mime(mime)
sym = mime.is_a?(Symbol) ? mime : mime.to_sym
class_eval <<-RUBY, __FILE__, __LINE__ + 1
def #{sym}(...)
custom(Mime[:#{sym}], ...)
end
RUBY
end
...
private
def method_missing(symbol, ...)
...
AbstractController::Collector.generate_method_for_mime(mime_constant)
public_send(symbol, ...)
...
end
end
end
GET /articles/1.json
Accept: application/json
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module AbstractController
module Collector
def self.generate_method_for_mime(mime)
sym = mime.is_a?(Symbol) ? mime : mime.to_sym
class_eval <<-RUBY, __FILE__, __LINE__ + 1
def #{sym}(...)
custom(Mime[:#{sym}], ...)
end
RUBY
end
...
private
def method_missing(symbol, ...)
...
AbstractController::Collector.generate_method_for_mime(mime_constant)
public_send(symbol, ...)
...
end
end
end
GET /articles/1.json
Accept: application/json
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module AbstractController
module Collector
def self.generate_method_for_mime(mime)
sym = mime.is_a?(Symbol) ? mime : mime.to_sym
class_eval <<-RUBY, __FILE__, __LINE__ + 1
def #{sym}(...)
custom(Mime[:#{sym}], ...)
end
RUBY
end
...
private
def method_missing(symbol, ...)
...
AbstractController::Collector.generate_method_for_mime(mime_constant)
public_send(symbol, ...)
...
end
end
end
def :json(β¦)
custom(Mime[:json], ...)
end
GET /articles/1.json
Accept: application/json
:json
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module AbstractController
module Collector
def self.generate_method_for_mime(mime)
sym = mime.is_a?(Symbol) ? mime : mime.to_sym
class_eval <<-RUBY, __FILE__, __LINE__ + 1
def #{sym}(...)
custom(Mime[:#{sym}], ...)
end
RUBY
end
...
private
def method_missing(symbol, ...)
...
AbstractController::Collector.generate_method_for_mime(mime_constant)
public_send(symbol, ...)
...
end
end
end
GET /articles/1.json
Accept: application/json
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module AbstractController
module Collector
def self.generate_method_for_mime(mime)
sym = mime.is_a?(Symbol) ? mime : mime.to_sym
class_eval <<-RUBY, __FILE__, __LINE__ + 1
def #{sym}(...)
custom(Mime[:#{sym}], ...)
end
RUBY
end
...
private
def method_missing(symbol, ...)
...
AbstractController::Collector.generate_method_for_mime(mime_constant)
public_send(symbol, ...)
...
end
end
end
GET /articles/1.json
Accept: application/json
:json
def json(...)
custom(Mime[:json], ...)
end
def json
...
end
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module AbstractController
module Collector
def self.generate_method_for_mime(mime)
sym = mime.is_a?(Symbol) ? mime : mime.to_sym
class_eval <<-RUBY, __FILE__, __LINE__ + 1
def #{sym}(...)
custom(Mime[:#{sym}], ...)
end
RUBY
end
...
private
def method_missing(symbol, ...)
...
AbstractController::Collector.generate_method_for_mime(mime_constant)
public_send(symbol, ...)
...
end
end
end
GET /articles/1.json
Accept: application/json
def json(...)
custom(Mime[:json], ...)
end
{
Mime[:json] => Proc.new { render json: @article }
}
:json
def json
...
end
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What does this module do?
class ArticlesController < ApplicationController
def show
@article = Article.find(params[:id])
respond_to do |format|
format.html # renders show.html.erb
format.json { render json: @article }
end
end
end
GET /articles/1.json
Accept: application/json
{
Mime[:json] => Proc.new { render json: @article }
}
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method_missing
class_eval
public_send
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Example 2:
Building Associations
ActiveRecord::Associations::Builder::Association
active_record/lib/active_record/associations/builder/association.rb
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https://api.rubyonrails.org/classes/ActiveRecord/Associations/
ClassMethods.html#method-i-belongs_to
Methods
Added By
belongs_to
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Examples
class Post < ActiveRecord::Base
belongs_to :author
end
post = Post.find(7)
author = Author.find(19)
post.author # similar to Author.find(post.author_id)
post.author = author # similar to post.author_id = author.id
post.build_author # similar to post.author = Author.new
post.create_author # similar to post.author = Author.new; post.author.save; post.author
post.create_author! # similar to post.author = Author.new; post.author.save!; post.author
post.reload_author
post.reset_author
post.author_changed?
post.author_previously_changed?
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Examples
class Post < ActiveRecord::Base
belongs_to :author
end
post = Post.find(7)
author = Author.find(19)
post.author # similar to Author.find(post.author_id)
post.author = author # similar to post.author_id = author.id
post.build_author # similar to post.author = Author.new
post.create_author # similar to post.author = Author.new; post.author.save; post.author
post.create_author! # similar to post.author = Author.new; post.author.save!; post.author
post.reload_author
post.reset_author
post.author_changed?
post.author_previously_changed?
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module ActiveRecord::Associations::Builder # :nodoc:
class Association # :nodoc:
...
def self.build(model, name, scope, options, &block)
if model.dangerous_attribute_method?(name)
raise ArgumentError, "You tried to define an association named #{name} on the model " \
"#{model.name}, but this will conflict with a method #{name} " \
"already defined by Active Record. Please choose a different " \
"association name."
end
reflection = create_reflection(model, name, scope, options, &block)
define_accessors(model, reflection)
define_callbacks(model, reflection)
define_validations(model, reflection)
define_change_tracking_methods(model, reflection)
reflection
end
...
end
end
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But first, what is a Reflection?
class Post < ApplicationRecord
belongs_to :author
has_many :comments
end
A re
fl
ection in Rails represents the
metadata about an association
between two Active Record models.
It contains details such as the type of
association, the associated class, &
options like foreign key constraints.
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But first, what is a Reflection?
class Post < ApplicationRecord
belongs_to :author
has_many :comments
end
A re
fl
ection in Rails represents the
metadata about an association
between two Active Record models.
It contains details such as the type of
association, the associated class, &
options like foreign key constraints.
reflection = Post.reflect_on_association(:author)
puts reflection.macro #=> :belongs_to
puts reflection.class_name #=> "Author"
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module ActiveRecord::Associations::Builder # :nodoc:
class Association # :nodoc:
...
def self.build(model, name, scope, options, &block)
if model.dangerous_attribute_method?(name)
raise ArgumentError, "You tried to define an association named #{name} on the model " \
"#{model.name}, but this will conflict with a method #{name} " \
"already defined by Active Record. Please choose a different " \
"association name."
end
reflection = create_reflection(model, name, scope, options, &block)
define_accessors(model, reflection)
define_callbacks(model, reflection)
define_validations(model, reflection)
define_change_tracking_methods(model, reflection)
reflection
end
...
end
end
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module ActiveRecord::Associations::Builder # :nodoc:
class Association # :nodoc:
...
def self.build(model, name, scope, options, &block)
...
reflection = create_reflection(model, name, scope, options, &block)
define_accessors(model, reflection)
define_callbacks(model, reflection)
define_validations(model, reflection)
define_change_tracking_methods(model, reflection)
reflection
end
...
end
end
define_accessors
post.author
post.author = author
class Post < ApplicationRecord
belongs_to :author
end
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module ActiveRecord::Associations::Builder # :nodoc:
class Association # :nodoc:
# Defines the setter & getter methods for the association
# class Post < ActiveRecord::Base
# has_many :comments
# end
#
# Post.first.comments & Post.first.comments= methods are defined by this method...
def self.define_accessors(model, reflection)
mixin = model.generated_association_methods
name = reflection.name
define_readers(mixin, name)
define_writers(mixin, name)
end
end
end
class Post < ApplicationRecord
belongs_to :author
end
post.author
post.author = author
Post::GeneratedAssociationMethods
define_accessors
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module ActiveRecord::Associations::Builder # :nodoc:
class Association # :nodoc:
# Defines the setter & getter methods for the association
# class Post < ActiveRecord::Base
# has_many :comments
# end
#
# Post.first.comments & Post.first.comments= methods are defined by this method...
def self.define_accessors(model, reflection)
mixin = model.generated_association_methods
name = reflection.name
define_readers(mixin, name)
define_writers(mixin, name)
end
end
end
define_readers(Post::GeneratedAssociationMethods, "author")
define_writers(Post::GeneratedAssociationMethods, "author")
define_accessors class Post < ApplicationRecord
belongs_to :author
end
post.author
post.author = author
Post::GeneratedAssociationMethods
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module ActiveRecord::Associations::Builder
class Association
def self.define_accessors(model, reflection)
mixin = model.generated_association_methods
name = reflection.name
define_readers(mixin, name)
define_writers(mixin, name)
end
def self.define_readers(mixin, name)
mixin.class_eval <<-CODE, __FILE__, __LINE__ + 1
def #{name}
association(:#{name}).reader
end
CODE
end
def self.define_writers(mixin, name)
mixin.class_eval <<-CODE, __FILE__, __LINE__ + 1
def #{name}=(value)
association(:#{name}).writer(value)
end
CODE
end
end
end
post.author
post.author = author
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module ActiveRecord::Associations::Builder
class Association
...
def self.define_readers(mixin, name)
mixin.class_eval <<-CODE, __FILE__, __LINE__ + 1
def #{name}
association(:#{name}).reader
end
CODE
end
def self.define_writers(mixin, name)
mixin.class_eval <<-CODE, __FILE__, __LINE__ + 1
def #{name}=(value)
association(:#{name}).writer(value)
end
CODE
end
end
end
def author
association(:author).reader
end
post.author
post.author = author
Post::GeneratedAssociationMethods "author"
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module ActiveRecord::Associations::Builder
class Association
...
def self.define_readers(mixin, name)
mixin.class_eval <<-CODE, __FILE__, __LINE__ + 1
def #{name}
association(:#{name}).reader
end
CODE
end
def self.define_writers(mixin, name)
mixin.class_eval <<-CODE, __FILE__, __LINE__ + 1
def #{name}=(value)
association(:#{name}).writer(value)
end
CODE
end
end
end
def author= author
association(:author).writer(author)
end
"author"
post.author
post.author = author
Post::GeneratedAssociationMethods
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module ActiveRecord::Associations::Builder
class Association
...
def self.define_readers(mixin, name)
mixin.class_eval <<-CODE, __FILE__, __LINE__ + 1
def #{name}
association(:#{name}).reader
end
CODE
end
def self.define_writers(mixin, name)
mixin.class_eval <<-CODE, __FILE__, __LINE__ + 1
def #{name}=(value)
association(:#{name}).writer(value)
end
CODE
end
end
end
def author= author
association(:author).writer(author)
end
post.author
post.author = author
def author
association(:author).reader
end
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# rails/activerecord/lib/active_record/associations/builder/belongs_to.rb
module ActiveRecord::Associations::Builder # :nodoc:
class BelongsTo < SingularAssociation # :nodoc:
...
def self.define_change_tracking_methods(model, reflection)
model.generated_association_methods.class_eval <<-CODE, __FILE__, __LINE__ + 1
def #{reflection.name}_changed?
association(:#{reflection.name}).target_changed?
end
def #{reflection.name}_previously_changed?
association(:#{reflection.name}).target_previously_changed?
end
CODE
end
...
end
end
Define Change Tracking Methods
post.author_changed?
post.author_previously_changed?
def author_changed?
association(:author).target_changed?
end
def author_previously_changed?
association(:author).target_previously_changed?
end
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# rails/activerecord/lib/active_record/associations/builder/singular_association.rb
module ActiveRecord::Associations::Builder # :nodoc:
class SingularAssociation < Association # :nodoc:
...
def self.define_accessors(model, reflection)
...
mixin.class_eval <<-CODE, __FILE__, __LINE__ + 1
def reload_#{name}
association(:#{name}).force_reload_reader
end
def reset_#{name}
association(:#{name}).reset
end
CODE
end
...
end
end
post.reload_author
post.reset_author
def reload_author
association(:author).force_reload_reader
end
def reset_author
association(:author).reset
end
Define Reload & Reset Methods
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# rails/activerecord/lib/active_record/associations/builder/singular_association.rb
module ActiveRecord::Associations::Builder # :nodoc:
class SingularAssociation < Association # :nodoc:
...
# Defines the (build|create)_association methods for
# belongs_to or has_one association
def self.define_constructors(mixin, name)
mixin.class_eval <<-CODE, __FILE__, __LINE__ + 1
def build_#{name}(*args, &block)
association(:#{name}).build(*args, &block)
end
def create_#{name}(*args, &block)
association(:#{name}).create(*args, &block)
end
def create_#{name}!(*args, &block)
association(:#{name}).create!(*args, &block)
end
CODE
end
...
end
end
post.build_author
post.create_author
post.create_author!
def build_author(*args, &block)
association(:author).build(*args, &block)
end
def create_author(*args, &block)
association(:author).create(*args, &block)
end
Define Constructors
def create_author!(*args, &block)
association(:author).create(*args, &block)
end
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Example 3:
Defining Autosave Validation Callbacks
ActiveRecord::AutosaveAssociation
active_record/lib/active_record/autosave_association.rb
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Autosave
Validations
class Post < ApplicationRecord
belongs_to :author
end
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module ActiveRecord
module AutosaveAssociation
module AssociationBuilderExtension # :nodoc:
def self.build(model, reflection)
...
end
...
end
module ClassMethods # :nodoc:
private
...
def define_autosave_validation_callbacks(reflection)
...
end
...
end
end
end
end
class Post < ApplicationRecord
belongs_to :author
end
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module ActiveRecord
module AutosaveAssociation
module ClassMethods # :nodoc:
private
def define_autosave_validation_callbacks(reflection)
validation_method = :"validate_associated_records_for_#{reflection.name}"
if reflection.validate? && !method_defined?(validation_method)
if reflection.collection?
method = :validate_collection_association
elsif reflection.has_one?
method = :validate_has_one_association
else
method = :validate_belongs_to_association
end
define_non_cyclic_method(validation_method) { send(method, reflection) }
validate validation_method
after_validation :_ensure_no_duplicate_errors
end
end
...
end
end
end
end
class Post < ApplicationRecord
belongs_to :author
end
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module ActiveRecord
module AutosaveAssociation
module ClassMethods # :nodoc:
private
def define_autosave_validation_callbacks(reflection)
validation_method = :"validate_associated_records_for_#{reflection.name}"
if reflection.validate? && !method_defined?(validation_method)
if reflection.collection?
method = :validate_collection_association
elsif reflection.has_one?
method = :validate_has_one_association
else
method = :validate_belongs_to_association
end
define_non_cyclic_method(validation_method) { send(method, reflection) }
validate validation_method
after_validation :_ensure_no_duplicate_errors
end
end
...
end
end
end
end
class Post < ApplicationRecord
belongs_to :author
end
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module ActiveRecord
module AutosaveAssociation
module ClassMethods # :nodoc:
private
def define_autosave_validation_callbacks(reflection)
validation_method = :"validate_associated_records_for_#{reflection.name}"
if reflection.validate? && !method_defined?(validation_method)
if reflection.collection?
method = :validate_collection_association
elsif reflection.has_one?
method = :validate_has_one_association
else
method = :validate_belongs_to_association
end
define_non_cyclic_method(validation_method) { send(method, reflection) }
validate validation_method
after_validation :_ensure_no_duplicate_errors
end
end
...
end
end
end
end
class Post < ApplicationRecord
belongs_to :author
end
:validate_associated_
records_for_author
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module ActiveRecord
module AutosaveAssociation
module ClassMethods # :nodoc:
private
def define_autosave_validation_callbacks(reflection)
validation_method = :"validate_associated_records_for_#{reflection.name}"
if reflection.validate? && !method_defined?(validation_method)
if reflection.collection?
method = :validate_collection_association
elsif reflection.has_one?
method = :validate_has_one_association
else
method = :validate_belongs_to_association
end
define_non_cyclic_method(validation_method) { send(method, reflection) }
validate validation_method
after_validation :_ensure_no_duplicate_errors
end
end
...
end
end
end
end
send(:validate_belongs_to_association,
)
class Post < ApplicationRecord
belongs_to :author
end
:validate_associated_
records_for_author
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module ActiveRecord
module AutosaveAssociation
module ClassMethods # :nodoc:
private
def define_autosave_validation_callbacks(reflection)
validation_method = :"validate_associated_records_for_#{reflection.name}"
if reflection.validate? && !method_defined?(validation_method)
if reflection.collection?
method = :validate_collection_association
elsif reflection.has_one?
method = :validate_has_one_association
else
method = :validate_belongs_to_association
end
define_non_cyclic_method(validation_method) { send(method, reflection) }
validate validation_method
after_validation :_ensure_no_duplicate_errors
end
end
...
end
end
end
end
send(:validate_belongs_to_association,
)
class Post < ApplicationRecord
belongs_to :author
end
:validate_associated_
records_for_author
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module ActiveRecord
module AutosaveAssociation
module ClassMethods # :nodoc:
private
def define_non_cyclic_method(name, &block)
return if method_defined?(name, false)
define_method(name) do |*args|
result = true; @_already_called ||= {}
# Loop prevention for validation of associations
unless @_already_called[name]
begin
@_already_called[name] = true
result = instance_eval(&block)
ensure
@_already_called[name] = false
end
end
result
end
end
...
end
end
end
end
class Post < ApplicationRecord
belongs_to :author
end
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module ActiveRecord
module AutosaveAssociation
module ClassMethods # :nodoc:
private
def define_non_cyclic_method(name, &block)
return if method_defined?(name, false)
define_method(name) do |*args|
result = true; @_already_called ||= {}
# Loop prevention for validation of associations
unless @_already_called[name]
begin
@_already_called[name] = true
result = instance_eval(&block)
ensure
@_already_called[name] = false
end
end
result
end
end
...
end
end
end
end
:validate_associated_
records_for_author
class Post < ApplicationRecord
belongs_to :author
end
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module ActiveRecord
module AutosaveAssociation
module ClassMethods # :nodoc:
private
def define_non_cyclic_method(name, &block)
return if method_defined?(name, false)
define_method(name) do |*args|
result = true; @_already_called ||= {}
# Loop prevention for validation of associations
unless @_already_called[name]
begin
@_already_called[name] = true
result = instance_eval(&block)
ensure
@_already_called[name] = false
end
end
result
end
end
...
end
end
end
end
define_method(:validate_associated_records_for_author)
class Post < ApplicationRecord
belongs_to :author
end
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module ActiveRecord
module AutosaveAssociation
module ClassMethods # :nodoc:
private
def define_non_cyclic_method(name, &block)
return if method_defined?(name, false)
define_method(name) do |*args|
result = true; @_already_called ||= {}
# Loop prevention for validation of associations
unless @_already_called[name]
begin
@_already_called[name] = true
result = instance_eval(&block)
ensure
@_already_called[name] = false
end
end
result
end
end
...
end
end
end
end
class Post < ApplicationRecord
belongs_to :author
end
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module ActiveRecord
module AutosaveAssociation
module ClassMethods # :nodoc:
private
def define_non_cyclic_method(name, &block)
return if method_defined?(name, false)
define_method(name) do |*args|
result = true; @_already_called ||= {}
# Loop prevention for validation of associations
unless @_already_called[name]
begin
@_already_called[name] = true
result = instance_eval(&block)
ensure
@_already_called[name] = false
end
end
result
end
end
...
end
end
end
end
class Post < ApplicationRecord
belongs_to :author
end
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module ActiveRecord
module AutosaveAssociation
module ClassMethods # :nodoc:
private
def define_non_cyclic_method(name, &block)
return if method_defined?(name, false)
define_method(name) do |*args|
result = true; @_already_called ||= {}
# Loop prevention for validation of associations
unless @_already_called[name]
begin
@_already_called[name] = true
result = instance_eval(&block)
ensure
@_already_called[name] = false
end
end
result
end
end
...
end
end
end
end
result = instance_eval
{ send(:validate_belongs_to_association,
) }
class Post < ApplicationRecord
belongs_to :author
end
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module ActiveRecord
module AutosaveAssociation
module ClassMethods # :nodoc:
private
def define_autosave_validation_callbacks(reflection)
validation_method = :"validate_associated_records_for_#{reflection.name}"
if reflection.validate? && !method_defined?(validation_method)
if reflection.collection?
method = :validate_collection_association
elsif reflection.has_one?
method = :validate_has_one_association
else
method = :validate_belongs_to_association
end
define_non_cyclic_method(validation_method) { send(method, reflection) }
validate validation_method
after_validation :_ensure_no_duplicate_errors
end
end
...
end
end
end
end
validate :validate_associated_records_for_author
class Post < ApplicationRecord
belongs_to :author
end
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module ActiveRecord
module AutosaveAssociation
module ClassMethods # :nodoc:
private
def define_autosave_validation_callbacks(reflection)
validation_method = :"validate_associated_records_for_#{reflection.name}"
if reflection.validate? && !method_defined?(validation_method)
if reflection.collection?
method = :validate_collection_association
elsif reflection.has_one?
method = :validate_has_one_association
else
method = :validate_belongs_to_association
end
define_non_cyclic_method(validation_method) { send(method, reflection) }
validate validation_method
after_validation :_ensure_no_duplicate_errors
end
end
...
end
end
end
end
validate :validate_associated_records_for_author
class Post < ApplicationRecord
belongs_to :author
end
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Benefits & Drawbacks
of Metaprogramming
in Rails
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Convention
over
Configuration
DRY
Principle
Dynamic
Behaviour
Simplifying
API Design
Benefits of Metaprogramming
in Rails
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Convention
over
Configuration
DRY
Principle
Dynamic
Behaviour
Simplifying
API Design
Benefits of Metaprogramming
in Rails
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Convention
over
Configuration
DRY
Principle
Dynamic
Behaviour
Simplifying
API Design
Benefits of Metaprogramming
in Rails
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Convention
over
Configuration
DRY
Principle
Dynamic
Behaviour
Simplifying
API Design
Benefits of Metaprogramming
in Rails
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Drawbacks of Metaprogramming
in Rails
Performance Overheads
Increased Abstraction
Maintainability Issues
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Drawbacks of Metaprogramming
in Rails
Performance Overheads
Increased Abstraction
Maintainability Issues
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Drawbacks of Metaprogramming
in Rails
Performance Overheads
Increased Abstraction
Maintainability Issues
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Our developer experience
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Using these
Patterns in the
Wild
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Dynamic Profile Fields
UserProfile.favourite_plant = "cactus"
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Dynamic Profile Fields
UserProfile.favourite_plant = "cactus" UserProfile.available_for_hire = true
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class Profile < ApplicationRecord
belongs_to :user
validates :user_id, uniqueness: true
validates :location, :website_url, length: { maximum: 100 }
validates :website_url, url: { allow_blank: true, no_local: true, schemes: %w[https http] }
validates_with ProfileValidator
ATTRIBUTE_NAME_REGEX = /(?\w+)=?/
CACHE_KEY = "profile/attributes".freeze
# Static fields are columns on the profiles table; they have no relationship
# to a ProfileField record. These are columns we can safely assume exist for
# any profile on a given Forem.
STATIC_FIELDS = %w[summary location website_url].freeze
# Update the Rails cache with the currently available attributes.
def self.refresh_attributes!
Rails.cache.delete(CACHE_KEY)
attributes
end
def self.attributes
Rails.cache.fetch(CACHE_KEY, expires_in: 24.hours) do
ProfileField.pluck(:attribute_name)
end
end
def self.static_fields
STATIC_FIELDS
end
def clear!
update(data: {})
end
# Lazily add accessors for profile fields on first use
def method_missing(method_name, *args, **kwargs, &block)
match = method_name.match(ATTRIBUTE_NAME_REGEX)
super unless match
field = ProfileField.find_by(attribute_name: match[:attribute_name])
super unless field
self.class.instance_eval do
store_accessor :data, field.attribute_name.to_sym
end
public_send(method_name, *args, **kwargs, &block)
end
# Defining this is not only a good practice in general, it's also necessary
# for `update` to work since the `_assign_attribute` helper it uses performs
# an explicit `responds_to?` check.
def respond_to_missing?(method_name, include_private = false)
match = method_name.match(ATTRIBUTE_NAME_REGEX)
return true if match && match[:attribute_name].in?(self.class.attributes)
super
end
end
https://github.com/forem/forem/
blob/main/app/models/profile.rb
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Empowering your Rails Journey
Explore,
Contribute, &
Grow
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Empowering your Rails Journey
Explore,
Contribute, &
Grow
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Empowering your Rails Journey
Explore,
Contribute, &
Grow
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Thank you! π
@Ridhwana_K