Rails：在 JSON 输出中包含相关对象

### 在Rails中，如何在JSON输出中包含相关对象

ruby
# user.rb
class User < ApplicationRecord
  has_many :posts
end
# post.rb
class Post < ApplicationRecord
  belongs_to :user
end

ruby
# users_controller.rb
class UsersController < ApplicationController
  def show
    @user = User.includes(:posts).find(params[:id])
    render json: @user, include: :posts
  end
end

ruby
# user.rb
class User < ApplicationRecord
  has_many :posts
  def as_json(options = {})
    super(options.merge(include: {
      posts: { only: [:title, :content] }
    }))
  end
end