Ruby on Railsのバリデーション【Active Recordによるデータチェックとエラーメッセージ】

# 新規プロジェクトの作成
$ rails new event-app
$ cd event-app

# scaffoldコマンドで各種モデルの関連ファイルを自動生成
$ rails generate scaffold event name:string hold_date:date
$ rails generate scaffold user name:string email:string password:string

# データベースの作成
$ rails db:create

# マイグレーションの実行
$ rails db:migrate

class Event < ApplicationRecord
  validates :name, presence: true
end

$ rails console

irb(main):001:0> event = Event.new
   (0.9ms)  SELECT sqlite_version(*)
=> #<Event:0x000002b12fb3c170 id: nil, name: nil, hold_date: nil, created_at: nil, updated_at: nil>

irb(main):002:0> event.name = ''
=> ""

irb(main):003:0> event.hold_date = Time.parse('20220101')
=> 2022-01-01 00:00:00 +0900

irb(main):004:0> event.save
=> false

irb(main):005:0> event.errors.full_messages
=> ["Name can't be blank"]

irb(main):006:0> event.name = 'sample event'
=> "sample event"

irb(main):007:0> event.valid?
=> true

irb(main):008:0> event.save
  TRANSACTION (0.1ms)  begin transaction
  Event Create (1.5ms)  INSERT INTO "events" ("name", "hold_date", "created_at", "updated_at") VALUES (?, ?, ?, ?)  [["name", "sample event"], ["hold_date", "2022-01-01"], ["created_at", "2021-11-07 06:23:04.564754"], ["updated_at", "2021-11-07 06:23:04.564754"]]
  TRANSACTION (3.4ms)  commit transaction
=> true

$ rails console

irb(main):001:0> event = Event.new
   (0.8ms)  SELECT sqlite_version(*)
=> #<Event:0x000002b5c0afe628 id: nil, name: nil, hold_date: nil, created_at: nil, updated_at: nil>

irb(main):002:0> event.name = ''
=> ""

irb(main):003:0> event.hold_date = Time.parse('20230101')
=> 2023-01-01 00:00:00 +0900

irb(main):004:0> event.save
=> false

irb(main):006:0> event.save!
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activerecord-6.1.4.1/lib/active_record/validations.rb:80:in `raise_validation_error': Validation failed: Name can't be blank (ActiveRecord::RecordInvalid)

class Event < ApplicationRecord
  validates :name, presence: true
  # validates :name, absence: true
  # validates :name, allow_blank: true
end

class Event < ApplicationRecord
  validates :name, acceptance: true
end

class User < ApplicationRecord
  validates :password, confirmation: true
  validates :password_confirmation, presence: true
  validates :email, confirmation: { case_sensitive: false }
  validates :email_confirmation, presence: true
end

<%= text_field :person, :email %>
<%= text_field :person, :email_confirmation %>

class Event < ApplicationRecord
  validates :name, length: { minimum: 5 }
  # validates :name, length: { maximum: 20 }
  # validates :name, length: { minimum: 5, maximum: 20 }
  # validates :name, length: { in: 5..20 }
  # validates :name, length: { is: 10 }
end

class Event < ApplicationRecord
  validates :name, uniqueness: true
  validates :name, uniqueness: { case_sensitive: false }
end

class Event < ApplicationRecord
  validates :capacity, numericality: true
end

class Event < ApplicationRecord
  validates :capacity, numericality: { only_integer: true }
  # validates :capacity, numericality: { greater_than: 100 }
  # validates :capacity, numericality: { greater_than_or_equal_to: 100 }
  # validates :capacity, numericality: { equal_to: 1000 }
  # validates :capacity, numericality: { less_than_or_equal_to: 20000 }
  # validates :capacity, numericality: { less_than: 20000 }
  # validates :capacity, numericality: { odd: true }
  # validates :capacity, numericality: { even: true }
end

class Event < ApplicationRecord
  validates :name, format: { with: /\A[a-zA-Z]+\z/ }
end

class Event < ApplicationRecord
  validates :status, inclusion: { in: %w(archive, in_session, scheduled) }
  validates :phase, exclusion: { in: %w(cancel, rehearsal) }
end

class Event < ApplicationRecord
  validates :name, presence: { message: "イベント名を入力してください。" }
end

class Event < ApplicationRecord
  validates :name, nuiqueness: { message: "%{value}はすでに使われています。" }
end

$ rails console

irb(main):001:0> event = Event.new
   (1.5ms)  SELECT sqlite_version(*)
=> #<Event:0x0000021f337d8fd0 id: nil, name: nil, hold_date: nil, created_at: nil, updated_at: nil>

irb(main):002:0> event.valid?
=> false

irb(main):003:0> event.errors.messages
=> {:name=>["can't be blank"]}

irb(main):004:0> event.errors.full_messages
=> ["Name can't be blank"]

<% if model.errors.any? %>
  <ul>
    <% model.errors.full_messages.each do |message| %>
      <li><%= message %></li>
    <% end %>
  </ul>
<% end %>

<%= form_for(@event) do |f|%>
<%= render 'layouts/errors', model: f.object %>

<% if event.errors.include?(:name) %>
  <p><%= event.errors.full_messages_for(:name).first %></p>
<% end %>

source 'https://rubygems.org'
git_source(:github) { |repo| "https://github.com/#{repo}.git" }

ruby '3.0.2'

gem 'rails-i18n'

...

$ bundle install

...

module EventApp
  class Application < Rails::Application
    config.load_defaults 6.1
    config.i18n.default_locale = :ja    # この行を追加
  end
end

ja:
  activerecord:
    attributes:
      event:
        name: "イベント名"
        hold_date: "開催日"

$ rails console

irb(main):001:0> event = Event.new
   (1.0ms)  SELECT sqlite_version(*)
=> #<Event:0x0000013bf42aac48 id: nil, name: nil, hold_date: nil, created_at: nil, updated_at: nil>

irb(main):002:0> event.valid?
=> false

irb(main):003:0> event.errors.full_messages
=> ["イベント名を入力してください"]