ActiveRecord6 の dirty attribute methods （will_save_change_to_* とか）の挙動一覧

ActiveRecord::AttributeMethods::Dirtyモジュールで定義している以下メソッドの挙動をまとめました。

• *_before_last_save
• *_in_database
• saved_change_to_*
• will_save_change_to_*?
• saved_change_to_*?
• *_change_to_be_saved
• saved_changes?
• saved_changes
• has_changes_to_save?
• changes_to_save
• changed_attribute_names_to_save
• attributes_in_database

※順番はテキトーです

以下のコードを1行ずつ実行し、各時点の dirty method の返り値を表にまとめました。

o = Obj.create(foo: "V1")
o.foo = "V2"
o.save!
o.foo = "V3"

一覧

active_record 6.0.2.2

Create record

  o = Obj.create(foo: "V1")

method	before_save	after_save	created
foo	"V1"	"V1"	"V1"
foo_before_last_save	nil	nil	nil
foo_in_database	nil	"V1"	"V1"
saved_change_to_foo	nil	[nil, "V1"]	[nil, "V1"]
will_save_change_to_foo?	true	false	false
saved_change_to_foo?	false	true	true
foo_change_to_be_saved	[nil, "V1"]	nil	nil
saved_changes?	false	true	true
saved_changes	{}	{"id"=>[nil, 1], "foo"=>[nil, "V1"]}	{"id"=>[nil, 1], "foo"=>[nil, "V1"]}
has_changes_to_save?	true	false	false
changes_to_save	{"foo"=>[nil, "V1"]}	{}	{}
changed_attribute_names_to_save	["foo"]	[]	[]
attributes_in_database	{"foo"=>nil}	{}	{}

Change record

  o.foo = "V2"

method	changed
foo	"V2"
foo_before_last_save	nil
foo_in_database	"V1"
saved_change_to_foo	[nil, "V1"]
will_save_change_to_foo?	true
saved_change_to_foo?	true
foo_change_to_be_saved	["V1", "V2"]
saved_changes?	true
saved_changes	{"id"=>[nil, 1], "foo"=>[nil, "V1"]}
has_changes_to_save?	true
changes_to_save	{"foo"=>["V1", "V2"]}
changed_attribute_names_to_save	["foo"]
attributes_in_database	{"foo"=>"V1"}

Save record

  o.save!

method	before_save	after_save	save finished
foo	"V2"	"V2"	"V2"
foo_before_last_save	nil	"V1"	"V1"
foo_in_database	"V1"	"V2"	"V2"
saved_change_to_foo	[nil, "V1"]	["V1", "V2"]	["V1", "V2"]
will_save_change_to_foo?	true	false	false
saved_change_to_foo?	true	true	true
foo_change_to_be_saved	["V1", "V2"]	nil	nil
saved_changes?	true	true	true
saved_changes	{"id"=>[nil, 1], "foo"=>[nil, "V1"]}	{"foo"=>["V1", "V2"]}	{"foo"=>["V1", "V2"]}
has_changes_to_save?	true	false	false
changes_to_save	{"foo"=>["V1", "V2"]}	{}	{}
changed_attribute_names_to_save	["foo"]	[]	[]
attributes_in_database	{"foo"=>"V1"}	{}	{}

Change record

  o.foo = "V3"

method	changed
foo	"V3"
foo_before_last_save	"V1"
foo_in_database	"V2"
saved_change_to_foo	["V1", "V2"]
will_save_change_to_foo?	true
saved_change_to_foo?	true
foo_change_to_be_saved	["V2", "V3"]
saved_changes?	true
saved_changes	{"foo"=>["V1", "V2"]}
has_changes_to_save?	true
changes_to_save	{"foo"=>["V2", "V3"]}
changed_attribute_names_to_save	["foo"]
attributes_in_database	{"foo"=>"V2"}

検証用に使用したスクリプト

# frozen_string_literal: true

require "bundler/inline"

ACTIVERECORD_VERSION = '6.0.2.2'

$stdout = open(File::NULL, "w") # Suppress migration log

gemfile(true) do
  source "https://rubygems.org"

  gem "activerecord", ACTIVERECORD_VERSION, require: "active_record"
  gem "sqlite3"
end

ActiveRecord::Base.establish_connection(
  adapter: "sqlite3",
  database: ":memory:",
)

ActiveRecord::Schema.define do
  create_table :objs do |t|
    t.string :foo, null: false
  end
end

$stdout = STDOUT

class Obj < ActiveRecord::Base
  METHODS = %i(
    foo
    foo_before_last_save
    foo_in_database
    saved_change_to_foo
    will_save_change_to_foo?
    saved_change_to_foo?
    foo_change_to_be_saved
    saved_changes?
    saved_changes
    has_changes_to_save?
    changes_to_save
    changed_attribute_names_to_save
    attributes_in_database
  ).freeze

  Captured = Struct.new(:context, :results)

  after_initialize :clear

  before_save do
    capture("before_save")
  end

  after_save do
    capture("after_save")
  end

  def capture(context)
    results = METHODS.map do |method|
      [method, public_send(method).inspect]
    end.to_h

    @captured << Captured.new(context, results)
  end

  def clear
    @captured = []
  end

  def inspect
    table = []

    table << "| method |" + @captured.map { |cap| " #{cap.context} " }.join("|") + "|"
    table << "|---" + ("|---" * @captured.length) + "|"

    METHODS.each do |method|
      table << "| `#{method}` |" + @captured.map { |cap| " `#{cap.results[method]}` " }.join("|") + "|"
    end

    table.join("\n") + "\n"
  end
end

BINDING = binding

def action(desc, code)
  puts <<~END
    ### #{desc}

    ```ruby
      #{code}
    ```

  END

  BINDING.eval(code)
end

puts "## active_record #{ACTIVERECORD_VERSION}\n\n"

o = action("Create record", 'o = Obj.create(foo: "V1")')
o.capture("created")
p o
o.clear

action("Change record", 'o.foo = "V2"')
o.capture("changed")
p o
o.clear

action("Save record", 'o.save!')
o.capture("save finished")
p o
o.clear

action("Change record", 'o.foo = "V3"')
o.capture("changed")
p o
o.clear

参考

• ActiveRecord 5 の dirty attribute methods （*_changed? とか）の挙動一覧 - Qiita
• Active Model の基礎 - Railsガイド
• Active Record コールバック - Railsガイド