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An Intervention for ActiveRecord Ernie Miller / @erniemiller / http://erniemiller.org

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Hi. https://github.com/ernie

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we’re hiring.* * “we’re hiring” is not part of the LivingSocial brand, but totally should be

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“You’re interesting to listen to.” ― Mom

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WARNING THE WARNING IN THE TALK DESCRIPTION, WHICH STATED THAT THERE WOULD BE ACTIVERECORD SOURCE CODE IN THIS TALK, WAS NOT A SCARE TACTIC.

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WARNING THE WARNING IN THE TALK DESCRIPTION, WHICH STATED THAT THERE WOULD BE ACTIVERECORD SOURCE CODE IN THIS TALK, WAS NOT A SCARE TACTIC. WE WILL BE READING ACTIVERECORD SOURCE CODE IN THIS TALK.

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WARNING THE WARNING IN THE TALK DESCRIPTION, WHICH STATED THAT THERE WOULD BE ACTIVERECORD SOURCE CODE IN THIS TALK, WAS NOT A SCARE TACTIC. WE WILL BE READING ACTIVERECORD SOURCE CODE IN THIS TALK. A LOT OF IT.

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WARNING THE WARNING IN THE TALK DESCRIPTION, WHICH STATED THAT THERE WOULD BE ACTIVERECORD SOURCE CODE IN THIS TALK, WAS NOT A SCARE TACTIC. WE WILL BE READING ACTIVERECORD SOURCE CODE IN THIS TALK. A LOT OF IT. THINGS MIGHT GET CRAZY.

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WARNING THE WARNING IN THE TALK DESCRIPTION, WHICH STATED THAT THERE WOULD BE ACTIVERECORD SOURCE CODE IN THIS TALK, WAS NOT A SCARE TACTIC. WE WILL BE READING ACTIVERECORD SOURCE CODE IN THIS TALK. A LOT OF IT. THINGS MIGHT GET CRAZY. WILL

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WARNING THE WARNING IN THE TALK DESCRIPTION, WHICH STATED THAT THERE WOULD BE ACTIVERECORD SOURCE CODE IN THIS TALK, WAS NOT A SCARE TACTIC. WE WILL BE READING ACTIVERECORD SOURCE CODE IN THIS TALK. A LOT OF IT. THERE IS STILL TIME TO ESCAPE. THINGS MIGHT GET CRAZY. WILL

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WHAT IS ACTIVE RECORD?

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“An object that wraps a row in a database table or view, encapsulates the database access, and adds domain logic on that data.” A PATTERN

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“Active Record has the primary advantage of simplicity. It’s easy to build Active Records, and they are easy to understand.” A PATTERN

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A LIBRARY class User < ActiveRecord::Base # name, email, and timestamps end

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A LIBRARY class User < ActiveRecord::Base # name, email, and timestamps end User.ancestors.size # => 57 User.methods.size # => 559 User.instance_methods.size # => 352

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A LIBRARY $ cloc lib/active_record ------------------------------ Language files code ------------------------------ Ruby 147 15836 YAML 1 11 ------------------------------ SUM: 148 15847 ------------------------------

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“Active Record has the primary advantage of simplicity. It’s easy to build Active Records, and they are easy to understand.”

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$ cloc lib/active_record ------------------------------ Language files code ------------------------------ Ruby 147 15836 YAML 1 11 ------------------------------ SUM: 148 15847 ------------------------------ User.ancestors.size # => 57 User.methods.size # => 559 User.instance_methods.size # => 352

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simplicity

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57 ancestors 559 class methods 352 instance methods

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easy to understand

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148 files 15,847 lines of code

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ActiveRecord Active Record

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ActiveRecord Active Record ≠

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I ActiveRecord

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...but...

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BUT

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ActiveRecord has issues

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I HAVE A THEORY

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NOBODY UNDERSTANDS ACTIVERECORD

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YOU ARE NOT THE EXCEPTION

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YOU ARE NOT THE EXCEPTION No. You’re not.

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Library LOC ActionMailer 527 ActiveModel 1,601 ActionController 2,557 ActionView 6,317 ActionDispatch 7,313 ActiveSupport 9,150 ActiveRecord 15,847

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“Magic is not inherently a bad word.” ― ActiveRecord README

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MAGIC REQUIRES CONVENTIONS

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MAGIC REQUIRES CONVENTIONS CONVENTIONS REQUIRE OPINIONS

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MAGIC REQUIRES CONVENTIONS OPINIONS ARE NOT CREATED EQUAL CONVENTIONS REQUIRE OPINIONS

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HOW TO CREATE A LEARNING CURVE

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HOW TO CREATE A LEARNING CURVE 1.Find things your users understand.

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HOW TO CREATE A LEARNING CURVE 1.Find things your users understand. 2.Ignore those things.

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OBJECT INITIALIZATION

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class User < ActiveRecord::Base def initialize(*) super self.name ||= '' end end user = User.new user.name # => ""

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class User < ActiveRecord::Base def initialize(*) super self.name ||= '' end end user = User.new user.name # => "" user = User.where(name: nil).first user.name # => nil

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class User < ActiveRecord::Base after_initialize :set_defaults def set_defaults self.name ||= '' end end user = User.new user.name # => "" user = User.where(name: nil).first user.name # => ""

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core.rb: def initialize(attributes = nil) defaults = self.class.column_defaults.dup defaults.each { |k, v| defaults[k] = v.dup if v.duplicable? } @attributes = self.class.initialize_attributes(defaults) @columns_hash = self.class.column_types.dup init_internals init_changed_attributes ensure_proper_type populate_with_current_scope_attributes assign_attributes(attributes) if attributes yield self if block_given? run_callbacks :initialize unless _initialize_callbacks.empty? end

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core.rb: def init_with(coder) @attributes = self.class.initialize_attributes( coder['attributes'] ) @columns_hash = self.class.column_types.merge( coder['column_types'] || {} ) init_internals @new_record = false run_callbacks :find run_callbacks :initialize self end

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core.rb: def init_with(coder) @attributes = self.class.initialize_attributes( coder['attributes'] ) @columns_hash = self.class.column_types.merge( coder['column_types'] || {} ) init_internals @new_record = false run_callbacks :find run_callbacks :initialize self end

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core.rb: def init_with(coder) @attributes = self.class.initialize_attributes( coder['attributes'] ) @columns_hash = self.class.column_types.merge( coder['column_types'] || {} ) init_internals @new_record = false run_callbacks :find run_callbacks :initialize self end

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persistence.rb: def instantiate(record, column_types = {}) klass = discriminate_class_for_record(record) column_types = klass.decorate_columns(column_types) klass.allocate.init_with( 'attributes' => record, 'column_types' => column_types ) end def find_by_sql(sql, binds = []) result_set = connection.select_all( sanitize_sql(sql), "#{name} Load", binds ) column_types = result_set.column_types result_set.map { |record| instantiate(record, column_types) } end querying.rb: * * Deprecation warning omitted

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persistence.rb: def instantiate(record, column_types = {}) klass = discriminate_class_for_record(record) column_types = klass.decorate_columns(column_types) klass.allocate.init_with( 'attributes' => record, 'column_types' => column_types ) end def find_by_sql(sql, binds = []) result_set = connection.select_all( sanitize_sql(sql), "#{name} Load", binds ) column_types = result_set.column_types result_set.map { |record| instantiate(record, column_types) } end querying.rb: * * Deprecation warning omitted

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persistence.rb: def instantiate(record, column_types = {}) klass = discriminate_class_for_record(record) column_types = klass.decorate_columns(column_types) klass.allocate.init_with( 'attributes' => record, 'column_types' => column_types ) end def find_by_sql(sql, binds = []) result_set = connection.select_all( sanitize_sql(sql), "#{name} Load", binds ) column_types = result_set.column_types result_set.map { |record| instantiate(record, column_types) } end querying.rb: * * Deprecation warning omitted

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TRADE-OFFS Understand them, then question them.

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ASSOCIATIONS

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ASSOCIATIONS Simple.

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ASSOCIATIONS Simple.Until they aren’t.

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POP QUIZ!

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class User < ActiveRecord::Base has_many :posts def assign_posts(post_or_posts) posts = Array(post_or_posts) posts.each { |post| post.published = false } self.posts += posts end end user.assign_posts posts user.posts.all? { |post| post.user_id == user.id } Q:

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A:

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I HAVE ABSOLUTELY NO IDEA. A:

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I HAVE ABSOLUTELY NO IDEA. A: Extra credit: “You’re not even testing the right attribute, genius.”

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Already Persisted? Already Persisted? After Assignment After Assignment User Posts Posts saved ID match

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class User < ActiveRecord::Base has_many :posts has_many :published_posts, -> { where published: true }, class_name: 'Post' end User.joins(:posts).where(posts: {title: 'zomg first post!'}) SELECT "users".* FROM "users" INNER JOIN "posts" ON "posts"."user_id" = "users"."id" WHERE "posts"."title" = 'zomg first post!'

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class User < ActiveRecord::Base has_many :posts has_many :published_posts, -> { where published: true }, class_name: 'Post' end User.joins(:posts).where(posts: {title: 'zomg first post!'}) User.joins(:published_posts). where(published_posts: {title: 'zomg first post!'}) SELECT "users".* FROM "users" INNER JOIN "posts" ON "posts"."user_id" = "users"."id" WHERE "posts"."title" = 'zomg first post!'

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class User < ActiveRecord::Base has_many :posts has_many :published_posts, -> { where published: true }, class_name: 'Post' end User.joins(:posts).where(posts: {title: 'zomg first post!'}) User.joins(:published_posts). where(published_posts: {title: 'zomg first post!'}) SELECT "users".* FROM "users" INNER JOIN "posts" ON "posts"."user_id" = "users"."id" WHERE "posts"."title" = 'zomg first post!' ActiveRecord::StatementInvalid

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relation/query_methods.rb: def build_where(opts, other = []) case opts when String, Array [@klass.send(:sanitize_sql, other.empty? ? opts : ([opts] + other))] when Hash attributes = @klass.send(:expand_hash_conditions_for_aggregates, opts) attributes.values.grep(ActiveRecord::Relation) do |rel| self.bind_values += rel.bind_values end PredicateBuilder.build_from_hash(klass, attributes, table) else [opts] end end

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relation/query_methods.rb: def build_where(opts, other = []) case opts when String, Array [@klass.send(:sanitize_sql, other.empty? ? opts : ([opts] + other))] when Hash attributes = @klass.send(:expand_hash_conditions_for_aggregates, opts) attributes.values.grep(ActiveRecord::Relation) do |rel| self.bind_values += rel.bind_values end PredicateBuilder.build_from_hash(klass, attributes, table) else [opts] end end

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relation/predicate_builder.rb: def self.build_from_hash(klass, attributes, default_table) queries = [] attributes.each do |column, value| table = default_table if value.is_a?(Hash) if value.empty? queries << '1=0' else table = Arel::Table.new(column, default_table.engine) association = klass.reflect_on_association(column.to_sym) value.each do |k, v| queries.concat expand(association && association.klass, table, k, v) end end else # ... end end queries end

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relation/predicate_builder.rb: def self.build_from_hash(klass, attributes, default_table) queries = [] attributes.each do |column, value| table = default_table if value.is_a?(Hash) if value.empty? queries << '1=0' else table = Arel::Table.new(column, default_table.engine) association = klass.reflect_on_association(column.to_sym) value.each do |k, v| queries.concat expand(association && association.klass, table, k, v) end end else # ... end end queries end

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class User < ActiveRecord::Base has_many :contributions has_many :posts, through: :contributions end class Post < ActiveRecord::Base has_many :contributions has_many :contributors, through: :contributions, source: :user end class Contribution < ActiveRecord::Base belongs_to :user belongs_to :post validates :role, presence: true end

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class User < ActiveRecord::Base has_many :contributions has_many :posts, through: :contributions end class Post < ActiveRecord::Base has_many :contributions has_many :contributors, through: :contributions, source: :user end class Contribution < ActiveRecord::Base belongs_to :user belongs_to :post validates :role, presence: true end

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post = Post.new(params[:post]) post.contributors = [current_user] post.save # => false

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post = Post.new(params[:post]) post.contributors = [current_user] post.contributions.first.role = 'author' # => NoMethodError: undefined method `role=' for nil:NilClass post = Post.new(params[:post]) post.contributors = [current_user] post.save # => false

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post = Post.new(params[:post]) post.contributors = [current_user] post.contributions.first.role = 'author' # => NoMethodError: undefined method `role=' for nil:NilClass contribution = current_user.contributions.build(role: 'author') contribution.build_post(params[:post]) contribution.save # => true post = Post.new(params[:post]) post.contributors = [current_user] post.save # => false

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class Post < ActiveRecord::Base has_many :contributions has_many :contributors, through: :contributions, source: :user has_many :authorships, -> { where role: 'author' }, class_name: 'Contribution' has_many :authors, through: :authorships, source: :user end post = Post.new(params[:post]) post.authors = [current_user] post.save # => true

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module ActiveRecord module Associations class HasManyThroughAssociation < HasManyAssociation # ... def concat_records(records) ensure_not_nested records = super if owner.new_record? && records records.flatten.each do |record| build_through_record(record) end end records end # ... end end end

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module ActiveRecord module Associations class HasManyThroughAssociation < HasManyAssociation # ... def concat_records(records) ensure_not_nested records = super if owner.new_record? && records records.flatten.each do |record| build_through_record(record) end end records end # ... end end end

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THE TESTS

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THE TESTS They lie.

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class Contribution < ActiveRecord::Base belongs_to :user belongs_to :post validates :user_id, presence: true validates :post_id, presence: true end

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class Contribution < ActiveRecord::Base belongs_to :user belongs_to :post validates :user_id, presence: true validates :post_id, presence: true end post = Post.new(params[:post]) post.contributors = [current_user] post.save # => false

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class Contribution < ActiveRecord::Base belongs_to :user belongs_to :post validates :user_id, presence: true validates :post_id, presence: true end post = Post.new(params[:post]) post.contributors = [current_user] post.save # => false

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class Contribution < ActiveRecord::Base belongs_to :user belongs_to :post validates :user_id, presence: true validates :post_id, presence: true end post = Post.new(params[:post]) post.contributors = [current_user] post.save # => false post.errors.messages # => {:contributions => ["is invalid"]}

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INVERSE_OF

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INVERSE_OF The oldest ActiveRecord feature you aren’t using

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user = User.first contribution = user.contributions.first user.equal?(contribution.user) # => false

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user = User.first contribution = user.contributions.first user.equal?(contribution.user) # => false

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class Post < ActiveRecord::Base has_many :contributions, inverse_of: :post has_many :contributors, through: :contributions, source: :user end class User < ActiveRecord::Base has_many :contributions, inverse_of: :user has_many :posts, through: :contributions end class Contribution < ActiveRecord::Base belongs_to :user belongs_to :post validates :user, presence: true validates :post, presence: true end

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class Post < ActiveRecord::Base has_many :contributions, inverse_of: :post has_many :contributors, through: :contributions, source: :user end class User < ActiveRecord::Base has_many :contributions, inverse_of: :user has_many :posts, through: :contributions end class Contribution < ActiveRecord::Base belongs_to :user belongs_to :post validates :user, presence: true validates :post, presence: true end

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class Post < ActiveRecord::Base has_many :contributions, inverse_of: :post has_many :contributors, through: :contributions, source: :user end class User < ActiveRecord::Base has_many :contributions, inverse_of: :user has_many :posts, through: :contributions end class Contribution < ActiveRecord::Base belongs_to :user belongs_to :post validates :user, presence: true validates :post, presence: true end

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Deep Thoughts

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Deep Thoughts on VALIDATIONS

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Deep Thoughts on VALIDATIONS

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Deep Thoughts on VALIDATIONS Validations live in Ruby.

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Deep Thoughts on VALIDATIONS

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Deep Thoughts on VALIDATIONS They should care about Ruby objects.

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Deep Thoughts on VALIDATIONS

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Deep Thoughts on VALIDATIONS “association_id” is an implementation detail.

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BUT MY ROFLSCALES!!!

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BUT MY ROFLSCALES!!! They’ll be fine.

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VALIDATES UNIQUENESS OF

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VALIDATES UNIQUENESS OF Doesn’t.

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VALIDATES UNIQUENESS OF Doesn’t. You know.

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VALIDATES UNIQUENESS OF Doesn’t. You know. Validate uniqueness of.

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“Using this validation method [...] does not guarantee the absence of duplicate record insertions.” ― validations/uniqueness.rb

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“The best way to work around this problem is to add a unique index to the database table.” ― validations/uniqueness.rb

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class User < ActiveRecord::Base validates :email, uniqueness: true end class CreateUsers < ActiveRecord::Migration def change create_table :users do |t| t.string :name t.string :email end add_index :users, :email, unique: true end end

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class User < ActiveRecord::Base def save(*) super rescue ActiveRecord::RecordNotUnique => e errors.add(:email, :taken) false end end User.create name: 'Ernie Miller', email: 'ernie@erniemiller.org' # => true user = User.create name: 'Ernie Miller', email: 'ernie@erniemiller.org' # => false user.errors.messages # => {:email => ["has already been taken"]}

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class Post < ActiveRecord::Base validates :title, uniqueness: { scope: :subtitle } end

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class Post < ActiveRecord::Base def save(*) super rescue ActiveRecord::RecordNotUnique => e attr_name, *scope = e.message. match(/Key \(([^\)]+)\)/)[1].split(/,\s*/) message = errors.generate_message(attr_name, :taken) if scope.any? message << " (scope: #{scope.to_sentence})" end errors.add attr_name, message false end end post = Post.create(title: 'Hello', subtitle: 'World!') # => false post.errors.messages # => {:title => ["has already been taken (scope: subtitle)"]}

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class Post < ActiveRecord::Base def save(*) super rescue ActiveRecord::RecordNotUnique => e attr_name, *scope = e.message. match(/Key \(([^\)]+)\)/)[1].split(/,\s*/) message = errors.generate_message(attr_name, :taken) if scope.any? message << " (scope: #{scope.to_sentence})" end errors.add attr_name, message false end end post = Post.create(title: 'Hello', subtitle: 'World!') # => false post.errors.messages # => {:title => ["has already been taken (scope: subtitle)"]}

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RELATION#MERGE

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RELATION#MERGE You’re using it.

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RELATION#MERGE You’re using it. A lot.

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def merged_wheres values[:where] ||= [] if values[:where].empty? || relation.where_values.empty? relation.where_values + values[:where] else # Remove equalities from the existing relation with a LHS which is # present in the relation being merged in. seen = Set.new values[:where].each { |w| if w.respond_to?(:operator) && w.operator == :== seen << w.left end } relation.where_values.reject { |w| w.respond_to?(:operator) && w.operator == :== && seen.include?(w.left) } + values[:where] end end relation/merger.rb:

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# We need to be able to support merging two relations without having # to get our hooks too deeply into Active Record. That proves to be # easier said than done. I hate Relation#merge. If Squeel has a # nemesis, Relation#merge would be it. # # Whatever code you see here currently is my current best attempt at # coexisting peacefully with said nemesis. def merge(r, equalities_resolved = false) if ::ActiveRecord::Relation === r && !equalities_resolved if self.table_name != r.table_name super(r.visited) else merge_resolving_duplicate_squeel_equalities(r) end else super(r) end end squeel/adapters/active_record/relation_extensions.rb:

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MERGES.

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SO

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MANY

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FREAKING

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MERGES.

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DEFAULT SCOPE

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DEFAULT SCOPE Can we please just kill it, already?

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Relation#exec_queries def exec_queries default_scoped = with_default_scope if default_scoped.equal?(self) @records = eager_loading? ? find_with_associations : @klass.find_by_sql(arel, bind_values) preload = preload_values preload += includes_values unless eager_loading? preload.each do |associations| ActiveRecord::Associations::Preloader.new(@records, associations).run end # @readonly_value is true only if set explicitly. @implicit_readonly is true if there # are JOINS and no explicit SELECT. readonly = readonly_value.nil? ? @implicit_readonly : readonly_value @records.each { |record| record.readonly! } if readonly else @records = default_scoped.to_a end @loaded = true @records end relation.rb:

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Relation#exec_queries def exec_queries default_scoped = with_default_scope if default_scoped.equal?(self) @records = eager_loading? ? find_with_associations : @klass.find_by_sql(arel, bind_values) preload = preload_values preload += includes_values unless eager_loading? preload.each do |associations| ActiveRecord::Associations::Preloader.new(@records, associations).run end # @readonly_value is true only if set explicitly. @implicit_readonly is true if there # are JOINS and no explicit SELECT. readonly = readonly_value.nil? ? @implicit_readonly : readonly_value @records.each { |record| record.readonly! } if readonly else @records = default_scoped.to_a end @loaded = true @records end relation.rb:

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Relation#with_default_scope def with_default_scope #:nodoc: if default_scoped? && default_scope = klass.send(:build_default_scope) default_scope = default_scope.merge(self) default_scope.default_scoped = false default_scope else self end end relation.rb:

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Relation#with_default_scope def with_default_scope #:nodoc: if default_scoped? && default_scope = klass.send(:build_default_scope) default_scope = default_scope.merge(self) default_scope.default_scoped = false default_scope else self end end relation.rb:

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Relation#build_default_scope def build_default_scope # :nodoc: if !Base.is_a?(method(:default_scope).owner) # The user has defined their own default scope method, so call that evaluate_default_scope { default_scope } elsif default_scopes.any? evaluate_default_scope do default_scopes.inject(relation) do |default_scope, scope| if !scope.is_a?(Relation) && scope.respond_to?(:call) default_scope.merge(unscoped { scope.call }) else default_scope.merge(scope) end end end end end scoping/default.rb:

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Relation#build_default_scope def build_default_scope # :nodoc: if !Base.is_a?(method(:default_scope).owner) # The user has defined their own default scope method, so call that evaluate_default_scope { default_scope } elsif default_scopes.any? evaluate_default_scope do default_scopes.inject(relation) do |default_scope, scope| if !scope.is_a?(Relation) && scope.respond_to?(:call) default_scope.merge(unscoped { scope.call }) else default_scope.merge(scope) end end end end end scoping/default.rb:

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Relation#build_default_scope def build_default_scope # :nodoc: if !Base.is_a?(method(:default_scope).owner) # The user has defined their own default scope method, so call that evaluate_default_scope { default_scope } elsif default_scopes.any? evaluate_default_scope do default_scopes.inject(relation) do |default_scope, scope| if !scope.is_a?(Relation) && scope.respond_to?(:call) default_scope.merge(unscoped { scope.call }) else default_scope.merge(scope) end end end end end scoping/default.rb:

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scope(name, scope_options = {}) “Adds a class method for retrieving and querying objects. A scope represents a narrowing of a database query.” ― scoping/named.rb

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SCOPES

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SCOPES Narrow your result set.

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SCOPES Narrow your result set. Just kidding.

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class User < ActiveRecord::Base default_scope -> { where(name: 'Jim') } scope :bobs, -> { where(name: 'Bob') } scope :toms, -> { where(name: 'Tom') } end User.where(name: 'Joe') User.bobs User.bobs.toms User.bobs.toms.where(name: 'Joe') User.where(name: 'Joe').bobs => Joe => Bob => Tom => Tom, Joe => Bob 4.0.0.beta1

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class User < ActiveRecord::Base default_scope -> { where(name: 'Jim') } scope :bobs, -> { where(name: 'Bob') } scope :toms, -> { where(name: 'Tom') } end User.where(name: 'Joe') User.bobs User.bobs.toms User.bobs.toms.where(name: 'Joe') User.where(name: 'Joe').bobs => Joe => Bob => Bob, Tom => Bob, Tom, Joe => Joe, Bob 4.0.0.rc1

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CALCULATIONS

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CALCULATIONS Those are the things you do with numbers, right?

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class Post < ActiveRecord::Base belongs_to :user def self.number_of_pages(page_size = 20) number_of_posts = self.count full_pages = number_of_posts / page_size if (number_of_posts % page_size).zero? full_pages else # We will have a page with remainders full_pages + 1 end end end

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class Post < ActiveRecord::Base belongs_to :user def self.number_of_pages(page_size = 20) number_of_posts = self.count full_pages = number_of_posts / page_size if (number_of_posts % page_size).zero? full_pages else # We will have a page with remainders full_pages + 1 end end end NoMethodError: undefined method `/' for #

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def perform_calculation(operation, column_name, options = {}) operation = operation.to_s.downcase distinct = self.distinct_value if operation == "count" column_name ||= (select_for_count || :all) unless arel.ast.grep(Arel::Nodes::OuterJoin).empty? distinct = true end column_name = primary_key if column_name == :all && distinct distinct = nil if column_name =~ /\s*DISTINCT\s+/i end if group_values.any? execute_grouped_calculation(operation, column_name, distinct) else execute_simple_calculation(operation, column_name, distinct) end end relation/calculations.rb: * * Deprecation warning omitted

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def perform_calculation(operation, column_name, options = {}) operation = operation.to_s.downcase distinct = self.distinct_value if operation == "count" column_name ||= (select_for_count || :all) unless arel.ast.grep(Arel::Nodes::OuterJoin).empty? distinct = true end column_name = primary_key if column_name == :all && distinct distinct = nil if column_name =~ /\s*DISTINCT\s+/i end if group_values.any? execute_grouped_calculation(operation, column_name, distinct) else execute_simple_calculation(operation, column_name, distinct) end end relation/calculations.rb: * * Deprecation warning omitted

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relation/calculations.rb: def execute_grouped_calculation(operation, column_name, distinct) #:nodoc: group_attrs = group_values if group_attrs.first.respond_to?(:to_sym) association = @klass.reflect_on_association(group_attrs.first.to_sym) associated = group_attrs.size == 1 && association && association.macro == :belongs_to # only count belongs_to associations group_fields = Array(associated ? association.foreign_key : group_attrs) else group_fields = group_attrs end group_aliases = group_fields.map { |field| column_alias_for(field) } group_columns = group_aliases.zip(group_fields).map { |aliaz,field| [aliaz, field] } group = group_fields if operation == 'count' && column_name == :all aggregate_alias = 'count_all' else aggregate_alias = column_alias_for([operation, column_name].join(' ')) end select_values = [

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relation/calculations.rb: def execute_grouped_calculation(operation, column_name, distinct) #:nodoc: group_attrs = group_values if group_attrs.first.respond_to?(:to_sym) association = @klass.reflect_on_association(group_attrs.first.to_sym) associated = group_attrs.size == 1 && association && association.macro == :belongs_to # only count belongs_to associations group_fields = Array(associated ? association.foreign_key : group_attrs) else group_fields = group_attrs end group_aliases = group_fields.map { |field| column_alias_for(field) } group_columns = group_aliases.zip(group_fields).map { |aliaz,field| [aliaz, field] } group = group_fields if operation == 'count' && column_name == :all aggregate_alias = 'count_all' else aggregate_alias = column_alias_for([operation, column_name].join(' ')) end select_values = [

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if association key_ids = calculated_data.collect { |row| row[group_aliases.first] } key_records = association.klass.base_class.find(key_ids) key_records = Hash[key_records.map { |r| [r.id, r] }] end Hash[calculated_data.map do |row| key = group_columns.map { |aliaz, col_name| column = calculated_data.column_types.fetch(aliaz) do column_for(col_name) end type_cast_calculated_value(row[aliaz], column) } key = key.first if key.size == 1 key = key_records[key] if associated [ key, type_cast_calculated_value( row[aggregate_alias], column_for(column_name), operation ) ] end] end

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if association key_ids = calculated_data.collect { |row| row[group_aliases.first] } key_records = association.klass.base_class.find(key_ids) key_records = Hash[key_records.map { |r| [r.id, r] }] end Hash[calculated_data.map do |row| key = group_columns.map { |aliaz, col_name| column = calculated_data.column_types.fetch(aliaz) do column_for(col_name) end type_cast_calculated_value(row[aliaz], column) } key = key.first if key.size == 1 key = key_records[key] if associated [ key, type_cast_calculated_value( row[aggregate_alias], column_for(column_name), operation ) ] end] end

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TL;DR

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CALLBACKS

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CALLBACKS You’ll be sorry.

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CALLBACKS You’ll be sorry. Don’t say I didn’t warn you.

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“That's a total of twelve callbacks, which gives you immense power to react and prepare for each state in the Active Record life cycle.” ― active_record/callbacks.rb

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class User < ActiveRecord::Base before_save NameSayer.new before_save :say_my_name before_save { |record| puts "My name is #{record.name}" } before_save 'puts "My name is #{self.name}"' # YES, REALLY def say_my_name puts "My name is #{self.name}" end end class NameSayer def before_save(record) puts "My name is #{record.name}" end end

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class User < ActiveRecord::Base before_save NameSayer.new before_save :say_my_name before_save { |record| puts "My name is #{record.name}" } before_save 'puts "My name is #{self.name}"' # YES, REALLY def say_my_name puts "My name is #{self.name}" end end class NameSayer def before_save(record) puts "My name is #{record.name}" end end

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class User < ActiveRecord::Base before_save NameSayer.new before_save :say_my_name before_save { |record| puts "My name is #{record.name}" } before_save 'puts "My name is #{self.name}"' # YES, REALLY def say_my_name puts "My name is #{self.name}" end end class NameSayer def before_save(record) puts "My name is #{record.name}" end end User.new._save_callbacks.class # => ActiveSupport::Callbacks::CallbackChain

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active_support/callbacks.rb: class CallbackChain < Array #:nodoc:# # ... def compile method = ["value = nil", "halted = false"] callbacks = "value = !halted && (!block_given? || yield)" reverse_each do |callback| callbacks = callback.apply(callbacks) end method << callbacks method << "value" method.join("\n") end # ... end

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active_support/callbacks.rb: class CallbackChain < Array #:nodoc:# # ... def compile method = ["value = nil", "halted = false"] callbacks = "value = !halted && (!block_given? || yield)" reverse_each do |callback| callbacks = callback.apply(callbacks) end method << callbacks method << "value" method.join("\n") end # ... end

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def apply(code) case @kind when :before <<-RUBY_EVAL if !halted && #{@compiled_options} # This double assignment is to prevent warnings in 1.9.3 as # the `result` variable is not always used except if the # terminator code refers to it. result = result = #{@filter} halted = (#{chain.config[:terminator]}) if halted halted_callback_hook(#{@raw_filter.inspect.inspect}) end end #{code} RUBY_EVAL when :after <<-RUBY_EVAL #{code} if #{!chain.config[:skip_after_callbacks_if_terminated] || "!halted"} && #{@compiled_options} #{@filter} end RUBY_EVAL when :around name = define_conditional_callback <<-RUBY_EVAL active_support/callbacks.rb:

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def apply(code) case @kind when :before <<-RUBY_EVAL if !halted && #{@compiled_options} # This double assignment is to prevent warnings in 1.9.3 as # the `result` variable is not always used except if the # terminator code refers to it. result = result = #{@filter} halted = (#{chain.config[:terminator]}) if halted halted_callback_hook(#{@raw_filter.inspect.inspect}) end end #{code} RUBY_EVAL when :after <<-RUBY_EVAL #{code} if #{!chain.config[:skip_after_callbacks_if_terminated] || "!halted"} && #{@compiled_options} #{@filter} end RUBY_EVAL when :around name = define_conditional_callback <<-RUBY_EVAL active_support/callbacks.rb:

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def apply(code) case @kind when :before <<-RUBY_EVAL if !halted && #{@compiled_options} # This double assignment is to prevent warnings in 1.9.3 as # the `result` variable is not always used except if the # terminator code refers to it. result = result = #{@filter} halted = (#{chain.config[:terminator]}) if halted halted_callback_hook(#{@raw_filter.inspect.inspect}) end end #{code} RUBY_EVAL when :after <<-RUBY_EVAL #{code} if #{!chain.config[:skip_after_callbacks_if_terminated] || "!halted"} && #{@compiled_options} #{@filter} end RUBY_EVAL when :around name = define_conditional_callback <<-RUBY_EVAL active_support/callbacks.rb:

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def apply(code) case @kind when :before <<-RUBY_EVAL if !halted && #{@compiled_options} # This double assignment is to prevent warnings in 1.9.3 as # the `result` variable is not always used except if the # terminator code refers to it. result = result = #{@filter} halted = (#{chain.config[:terminator]}) if halted halted_callback_hook(#{@raw_filter.inspect.inspect}) end end #{code} RUBY_EVAL when :after <<-RUBY_EVAL #{code} if #{!chain.config[:skip_after_callbacks_if_terminated] || "!halted"} && #{@compiled_options} #{@filter} end RUBY_EVAL when :around name = define_conditional_callback <<-RUBY_EVAL active_support/callbacks.rb:

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halted = (#{chain.config[:terminator]}) if halted halted_callback_hook(#{@raw_filter.inspect.inspect}) end end #{code} RUBY_EVAL when :after <<-RUBY_EVAL #{code} if #{!chain.config[:skip_after_callbacks_if_terminated] || "!halted"} && #{@compiled_options} #{@filter} end RUBY_EVAL when :around name = define_conditional_callback <<-RUBY_EVAL #{name}(halted) do #{code} value end RUBY_EVAL end end

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active_support/callbacks.rb: class Callback #:nodoc:# @@_callback_sequence = 0 attr_accessor :chain, :filter, :kind, :options, :klass, :raw_filter def initialize(chain, filter, kind, options, klass) @chain, @kind, @klass = chain, kind, klass deprecate_per_key_option(options) normalize_options!(options) @raw_filter, @options = filter, options @filter = _compile_filter(filter) recompile_options! end # ... end

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active_support/callbacks.rb: class Callback #:nodoc:# @@_callback_sequence = 0 attr_accessor :chain, :filter, :kind, :options, :klass, :raw_filter def initialize(chain, filter, kind, options, klass) @chain, @kind, @klass = chain, kind, klass deprecate_per_key_option(options) normalize_options!(options) @raw_filter, @options = filter, options @filter = _compile_filter(filter) recompile_options! end # ... end

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active_support/callbacks.rb: class Callback #:nodoc:# @@_callback_sequence = 0 attr_accessor :chain, :filter, :kind, :options, :klass, :raw_filter def initialize(chain, filter, kind, options, klass) @chain, @kind, @klass = chain, kind, klass deprecate_per_key_option(options) normalize_options!(options) @raw_filter, @options = filter, options @filter = _compile_filter(filter) recompile_options! end # ... end

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active_support/callbacks.rb: def recompile_options! conditions = ["true"] unless options[:if].empty? conditions << Array(_compile_filter(options[:if])) end unless options[:unless].empty? conditions << Array(_compile_filter(options[:unless])). map {|f| "!#{f}"} end @compiled_options = conditions.flatten.join(" && ") end

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active_support/callbacks.rb: def recompile_options! conditions = ["true"] unless options[:if].empty? conditions << Array(_compile_filter(options[:if])) end unless options[:unless].empty? conditions << Array(_compile_filter(options[:unless])). map {|f| "!#{f}"} end @compiled_options = conditions.flatten.join(" && ") end

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def _compile_filter(filter) @_is_object_filter = false case filter when Array filter.map {|f| _compile_filter(f)} when Symbol filter when String "(#{filter})" when Proc method_name = "_callback_#{@kind}_#{next_id}" @klass.send(:define_method, method_name, &filter) return method_name if filter.arity <= 0 method_name << (filter.arity == 1 ? "(self)" : " self, Proc.new ") else method_name = _method_name_for_object_filter(kind, filter) @_is_object_filter = true @klass.send(:define_method, "#{method_name}_object") { filter } _normalize_legacy_filter(kind, filter) scopes = Array(chain.config[:scope]) method_to_call = scopes.map{ |s| s.is_a?(Symbol) ? send(s) : s }.join("_") @klass.class_eval <<-RUBY_EVAL, __FILE__, __LINE__ + 1 def #{method_name}(&blk) active_support/callbacks.rb:

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when String "(#{filter})" when Proc method_name = "_callback_#{@kind}_#{next_id}" @klass.send(:define_method, method_name, &filter) return method_name if filter.arity <= 0 method_name << (filter.arity == 1 ? "(self)" : " self, Proc.new ") else method_name = _method_name_for_object_filter(kind, filter) @_is_object_filter = true @klass.send(:define_method, "#{method_name}_object") { filter } _normalize_legacy_filter(kind, filter) scopes = Array(chain.config[:scope]) method_to_call = scopes.map{ |s| s.is_a?(Symbol) ? send(s) : s }.join("_") @klass.class_eval <<-RUBY_EVAL, __FILE__, __LINE__ + 1 def #{method_name}(&blk) #{method_name}_object.send(:#{method_to_call}, self, &blk) end RUBY_EVAL method_name end end

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value = nil halted = false if !halted && true # This double assignment is to prevent warnings in 1.9.3 as # the `result` variable is not always used except if the # terminator code refers to it. result = result = _callback_before_15 halted = (result == false) if halted halted_callback_hook("#") end end if !halted && true # This double assignment is to prevent warnings in 1.9.3 as # the `result` variable is not always used except if the # terminator code refers to it. result = result = say_my_name halted = (result == false) if halted halted_callback_hook(":say_my_name") end end if !halted && true # This double assignment is to prevent warnings in 1.9.3 as # the `result` variable is not always used except if the # terminator code refers to it. result = result = _callback_before_17(self)

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if !halted && true # This double assignment is to prevent warnings in 1.9.3 as # the `result` variable is not always used except if the # terminator code refers to it. result = result = _callback_before_17(self) halted = (result == false) if halted halted_callback_hook("#") end end if !halted && true # This double assignment is to prevent warnings in 1.9.3 as # the `result` variable is not always used except if the # terminator code refers to it. result = result = (puts "My name is #{self.name}") halted = (result == false) if halted halted_callback_hook("\"puts \\\"My name is \\\#{self.name}\\\"\"") end end value = !halted && (!block_given? || yield) value

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if !halted && true # This double assignment is to prevent warnings in 1.9.3 as # the `result` variable is not always used except if the # terminator code refers to it. result = result = _callback_before_17(self) halted = (result == false) if halted halted_callback_hook("#") end end if !halted && true # This double assignment is to prevent warnings in 1.9.3 as # the `result` variable is not always used except if the # terminator code refers to it. result = result = (puts "My name is #{self.name}") halted = (result == false) if halted halted_callback_hook("\"puts \\\"My name is \\\#{self.name}\\\"\"") end end value = !halted && (!block_given? || yield) value

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active_support/callbacks.rb: module ClassMethods def __define_callbacks(kind, object) #:nodoc: name = __callback_runner_name(kind) unless object.respond_to?(name, true) str = object.send("_#{kind}_callbacks").compile class_eval <<-RUBY_EVAL, __FILE__, __LINE__ + 1 def #{name}() #{str} end protected :#{name} RUBY_EVAL end name end end def run_callbacks(kind, &block) runner_name = self.class.__define_callbacks(kind, self) send(runner_name, &block) end

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active_record/callbacks.rb: module Callbacks def destroy #:nodoc: run_callbacks(:destroy) { super } end def touch(*) #:nodoc: run_callbacks(:touch) { super } end private def create_or_update #:nodoc: run_callbacks(:save) { super } end def create_record #:nodoc: run_callbacks(:create) { super } end def update_record(*) #:nodoc: run_callbacks(:update) { super } end end

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A NOVEL IDEA!

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INHERITANCE AND SUPER

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BEFORE FILTER!!! class User < ActiveRecord::Base def create_or_update say_my_name && super end def say_my_name puts "My name is #{name}"; true end end

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BEFORE FILTER!!! class User < ActiveRecord::Base def create_or_update say_my_name && super end def say_my_name puts "My name is #{name}"; true end end

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AFTER FILTER!!! class User < ActiveRecord::Base def create_or_update super && final_stuff or raise ActiveRecord::Rollback end def final_stuff puts "IMPORTANT FINAL STUFF" end end

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AFTER FILTER!!! class User < ActiveRecord::Base def create_or_update super && final_stuff or raise ActiveRecord::Rollback end def final_stuff puts "IMPORTANT FINAL STUFF" end end

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AROUND FILTER!!! class User < ActiveRecord::Base def create_or_update puts "GET READY" unless sneak_attack? super puts "WASN'T THAT EXCITING?" if awesome? end end

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AROUND FILTER!!! class User < ActiveRecord::Base def create_or_update puts "GET READY" unless sneak_attack? super puts "WASN'T THAT EXCITING?" if awesome? end end

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“That's a total of twelve callbacks, which gives you immense power to react and prepare for each state in the Active Record life cycle.” ― active_record/callbacks.rb

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“That’s Ruby, which gives you immense power to do, you know, pretty much anything, ever.” ― me

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SO?

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ACTIVERECORD WORKS WELL ENOUGH

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IT’S BIG AND COMPLEX, CHANGE WILL BE HARD

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CHANGES WILL INTENTIONALLY BREAK MY STUFF

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CHANGES WILL ACCIDENTALLY BREAK MY STUFF

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USE SOMETHING ELSE WHEN YOU NEED TO

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LEGACY ACTIVERECORD IS

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LEGACY ACTIVERECORD IS OUR

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IT DESERVES BETTER

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NEW USERS DESERVE BETTER

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WE CAN DO BETTER

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WRITE SOME DOCS

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WRITE SOME TESTS

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TRIAGE SOME ISSUES

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PARTICIPATE IN THE DISCUSSION

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BETTER STARTS NOW.

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Ernie Miller / @erniemiller / http://erniemiller.org THANK YOU!