Creating Nested Resources in Ruby on Rails

🧠 Technical Summary

This guide teaches the concept of nested resources in Ruby on Rails projects. The goal is to establish a logical relationship between the main model (e.g. Shark) and the submodel (e.g. Post) and manage CRUD operations in accordance with this hierarchy.

Steps:

• Creation of the Post model,
• Defining the relationship in the Shark model,
• Intertwining the route,
• Editing controller and view files,
• Adding validation and testing the application.

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🎯 What You Will Learn in This Guide

• The basics of the Nested resources structure,
• The difference between belongs_to and has_many relationships,
• Managing nested controller structures,
• Correct configuration of forms and routes,
• Making data relationships more organized in Rails.

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⚙️ 1. Creating Nested Models and Resources

Switch to the project and create the model Post:

cd sharkapp
rails generate scaffold Post body:text shark:references

This command creates the Post model, establishes its relationship with Shark, and creates the necessary files for CRUD operations.

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🧩 2. Updating Parent Models and Routes

Add Relationship to Shark Model

# ~/sharkapp/app/models/shark.rb
class Shark < ApplicationRecord
  has_many :posts, dependent: :destroy
  validates :name, presence: true, uniqueness: true
  validates :facts, presence: true
end

dependent: :destroy, when a shark is deleted it also removes all posts belonging to it.

Configure Nested Routes

# ~/sharkapp/config/routes.rb
Rails.application.routes.draw do
  resources :sharks do
    resources :posts
  end
  root 'sharks#index'
end

Routes now have the following structure: /sharks/:shark_id/posts/:id

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🧠 3. Adapting the Controller to Nested Structure

Open app/controllers/posts_controller.rb:

class PostsController < ApplicationController
  before_action :get_shark
  before_action :set_post, only: [:show, :edit, :update, :destroy]

  def index
    @posts = @shark.posts
  end

  def new
    @post = @shark.posts.build
  end

  def create
    @post = @shark.posts.build(post_params)
    if @post.save
      redirect_to shark_posts_path(@shark), notice: 'Gönderi başarıyla oluşturuldu.'
    else
      render :new
    end
  end

  def update
    if @post.update(post_params)
      redirect_to shark_posts_path(@shark), notice: 'Gönderi güncellendi.'
    else
      render :edit
    end
  end

  def destroy
    @post.destroy
    redirect_to shark_posts_path(@shark), notice: 'Gönderi silindi.'
  end

  private

  def get_shark
    @shark = Shark.find(params[:shark_id])
  end

  def set_post
    @post = @shark.posts.find(params[:id])
  end

  def post_params
    params.require(:post).permit(:body, :shark_id)
  end
end

This controller only acts on posts belonging to the selected shark.

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🧱 4. Editing Views

_form.html.erb

<%= form_with(model: [@shark, post], local: true) do |form| %>
  <%= form.label :body, 'Gönderi İçeriği' %>
  <%= form.text_area :body %>
  <%= form.submit 'Kaydet' %>
<% end %>

The form automatically links the post to the relevant shark.

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index.html.erb

<h1>Gönderiler</h1>
<table>
  <thead>
    <tr>
      <th>İçerik</th>
      <th>Köpek Balığı</th>
      <th>İşlemler</th>
    </tr>
  </thead>
  <tbody>
    <% @posts.each do |post| %>
      <tr>
        <td><%= post.body %></td>
        <td><%= post.shark.name %></td>
        <td>
          <%= link_to 'Düzenle', edit_shark_post_path(@shark, post) %> |
          <%= link_to 'Sil', [@shark, post], method: :delete, data: { confirm: 'Emin misiniz?' } %>
        </td>
      </tr>
    <% end %>
  </tbody>
</table>

<%= link_to 'Yeni Gönderi', new_shark_post_path(@shark) %>

The view lists only posts from the selected shark.

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sharks/show.html.erb

<h2><%= @shark.name %> Hakkında Gönderiler</h2>

<ul>
  <% @shark.posts.each do |post| %>
    <li><%= post.body %></li>
  <% end %>
</ul>

<%= link_to 'Yeni Gönderi Ekle', new_shark_post_path(@shark) %> |
<%= link_to 'Geri Dön', sharks_path %>

User can add new post directly from shark detail page.

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✅ 5. Model Validation

Update the app/models/post.rb file:

class Post < ApplicationRecord
  belongs_to :shark
  validates :body, presence: true, uniqueness: true
end

This verification prevents duplicate or empty posts.

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🧪 6. Testing the App

Run database migrations:

rails db:migrate

Start the server:

rails s

Test the app from the browser:

http://localhost:3000

You can now view, edit and delete posts specific to each shark.

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❓ Frequently Asked Questions (FAQ)

1. Why are nested resources used? To establish a logical relationship where one model (e.g. Post) depends on another model (e.g. Shark).

2. What is the difference between has_many and belongs_to? has_many represents the upper model, belongs_to represents the lower model.

3. Why is dependent: :destroy added? Deleting the parent ensures that all dependent records are also deleted.

4. Can I create a model instead of scaffold? Yes, but scaffold speeds up the process by automatically building the entire CRUD structure.

5. Are three levels of nested structure recommended? No, Rails recommends a maximum of two levels (e.g. shark → post).

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🎯 Result

Congratulations! You can now set up the nested resources structure in Ruby on Rails projects and manage relationships between models. 💡 You can try this structure in your own project on GenixNode right now.