1対多のリレーションでも保存の方法の違いが紛らしいな

1番基本

1つ1つリレーションを作るパターン

## リレーション

User 1 - * Post

## user.rb
has_many :posts

## post.rb
belongs_to :user

## controller

def new
  @post = Post.new

def create
  @post = Post.new(post_params)

private

def post_params

  params.require(:post).permit(:name, :body).merge(user_id: current_user.id)

## view
= form_for @post do |form|

  = form.label :title
  = form.text_field :title

  = form.label :body
  = form.text_field :body
  = form.submit '送信'

## 要点

1つ1つ userとpostの繋がりを作っていくパターン

複数一気に作るパターン

パターン1（子要素のデータがある場合）

xx_idsを使う

## リレーション
User 1 - * Skill

## user.rb
has_many :skills

## skill.rb
belongs_to :user


## 子要素のデータ存在する

Skill
  id1 name: "筋トレ"
  id2 name: "イケメン"
  id3 name: "話術"

## controller

def new
  @user = User.new

private

def post_params

  params.require(:post).permit(:name, skill_ids: [])

## view

= form_for @user do |f|
  = f.label :name
  = f.text_field :name  
  = f.fields_for :skill_ids do |skill|
    = skill.collection_select :name, Skill.all, :id, :name  
  = f.submit "送信"

パターン2（子要素のデータがない場合）

accepts_nested_attributes_for使う


## リレーション
User 1 - * Address

## user.rb
  has_many :addresses
  accepts_nested_attributes_for :addresses,allow_destroy: true
  
## address.rb
 - state
 - city
 belongs_to :user

## controller

  def new 
    @user = User.new
    @user.addresses.build

  private
  def user_params
      params.require(:user).permit(:name, addresses_attributes: [:id, :state, :city])
    end

## view
= form_for @user do |form|
  .field
    = form.label :name
    = form.text_field :name
  .fidle
    = form.fields_for :addresses do |address|
      = address.label :state
      = address.text_field :state
      = address.label :city
      = address.text_field :city
  .fidle
    = form.fields_for :addresses do |address|
      = address.label :state
      = address.text_field :state
      = address.label :city
      = address.text_field :city