RoR 3 - 查找一组孩子的父母名单

# app/models/child.rb
class Child < ApplicationRecord
  belongs_to :parent
end

# app/models/parent.rb
class Parent < ApplicationRecord
  has_many :children
end

$ rails generate migration CreateChildren parent:references name:string
$ rails generate migration CreateParents name:string
$ rails db:migrate

# db/seeds.rb
parent1 = Parent.create(name: "John")
parent2 = Parent.create(name: "Jane")

Child.create(name: "Child1", parent: parent1)
Child.create(name: "Child2", parent: parent1)
Child.create(name: "Child3", parent: parent2)

# app/controllers/children_controller.rb
class ChildrenController < ApplicationController
  def index
    @children = Child.all
  end
end

# config/routes.rb
Rails.application.routes.draw do
  resources :children, only: [:index]
end

<!-- app/views/children/index.html.erb -->
<h1>Children's Parents</h1>

<ul>
  <% @children.each do |child| %>
    <li><%= child.name %> - <%= child.parent.name %></li>
  <% end %>
</ul>