# model作成
$ rails generate model user name:string email:string
# マイグレーションファイル実行(DBに反映)
$ rails db:migrate

$ rails generate migration add_index_to_users_email
$ rails generate migration add_password_digest_to_users password_digest:string
# エラー時のお役立ちコマンド
$ rails generate destoroy user
$ rails db:migrate:reset

##メソッド

new
新しいユーザーオブジェクトを生成

>> user = User.new(name: "Michael Hartl", email: "michael@example.com")
=> #<User id: nil, name: "Michael Hartl", email: "michael@example.com",
created_at: nil, updated_at: nil>

valid?
オブジェクトが有効かどうか

>> user.valid?
true

save
DBにUserオブジェクトを保存

>> user.save
   (0.1ms)  SAVEPOINT active_record_1
  SQL (0.8ms)  INSERT INTO "users" ("name", "email", "created_at",
  "updated_at") VALUES (?, ?, ?, ?)  [["name", "Michael Hartl"],
  ["email", "michael@example.com"], ["created_at", "2019-08-22 01:51:03.453035"],
  ["updated_at", "2019-08-22 01:51:03.453035"]]
   (0.1ms)  RELEASE SAVEPOINT active_record_1
=> true

create
モデルの生成(new)と保存(save)を同時に行う

>> User.create(name: "A Nother", email: "another@example.org")
#<User id: 2, name: "A Nother", email: "another@example.org", created_at:
"2019-08-22 01:53:22", updated_at: "2019-08-22 01:53:22">

# 変数fooに代入
>> foo = User.create(name: "Foo", email: "foo@bar.com")
#<User id: 3, name: "Foo", email: "foo@bar.com", created_at: "2019-08-22
01:54:03", updated_at: "2019-08-22 01:54:03">

destroy
createの逆で削除(ただしメモリには残る)

>> foo.destroy
   (0.1ms)  SAVEPOINT active_record_1
  SQL (0.2ms)  DELETE FROM "users" WHERE "users"."id" = ?  [["id", 3]]
   (0.1ms)  RELEASE SAVEPOINT active_record_1
=> #<User id: 3, name: "Foo", email: "foo@bar.com", created_at: "2019-08-22
01:54:03", updated_at: "2019-08-22 01:54:03">

find, find_by
オブジェクトを検索

#エラー出したい場合
>> User.find(1)
=> #<User id: 1, name: "Michael Hartl", email: "michael@example.com",
created_at: "2019-08-22 01:51:03", updated_at: "2019-08-22 01:51:03">

# 属性(email)で検索。エラー出さないで表示
>> User.find_by(email: "michael@example.com")
=> #<User id: 1, name: "Michael Hartl", email: "michael@example.com",
created_at: "2019-08-22 01:51:03", updated_at: "2019-08-22 01:51:03">

first
DBの最初のユーザー

>> User.first
=> #<User id: 1, name: "Michael Hartl", email: "michael@example.com",
created_at: "2019-08-22 01:51:03", updated_at: "2019-08-22 01:51:03">

all
DB全てのUserオブジェクト

>> User.all
=> #<ActiveRecord::Relation [#<User id: 1, name: "Michael Hartl", email:
"michael@example.com", created_at: "2019-08-22 01:51:03", updated_at:
"2019-08-22 01:51:03">, #<User id: 2, name: "A Nother", email:
"another@example.org", created_at: "2019-08-22 01:53:22", updated_at:
"2019-08-22 01:53:22">]>

update
オブジェクトを更新

>> user.update(name: "The Dude", email: "dude@abides.org")
=> true
>> user.name
=> "The Dude"
>> user.email
=> "dude@abides.org"

# 検証を回避して更新したい
>> user.update_attribute(:name, "El Duderino")
=> true
>> user.name
=> "El Duderino"

errors
エラー内容表示

>> user = User.new(name: "", email: "michael@example.com")
>> user.valid?
=> false
>> user.errors.full_messages
=> ["Name can't be blank"]