Rails Controller Patterns

Patterns for building well-structured Rails controllers.

When This Skill Applies

• Implementing RESTful controller actions
• Handling request parameters safely
• Setting up before_action filters
• Managing response formats
• Designing routes
• Error handling in controllers

Core Principles

Thin Controllers

Controllers should:

• Handle HTTP concerns (params, session, response)
• Delegate business logic to models/services
• Keep actions under 10 lines

RESTful Design

Stick to standard CRUD actions:

• index, show, new, create, edit, update, destroy
• Add custom actions sparingly

Detailed Documentation

• patterns.md – Controller patterns and examples

Controller Structure

class PostsController < ApplicationController
  # 1. Before actions
  before_action :authenticate_user!
  before_action :set_post, only: [:show, :edit, :update, :destroy]

  # 2. Actions (CRUD order)
  def index
    @posts = Post.recent.page(params[:page])
  end

  def show
  end

  def new
    @post = current_user.posts.build
  end

  def create
    @post = current_user.posts.build(post_params)

    if @post.save
      redirect_to @post, notice: 'Post created.'
    else
      render :new, status: :unprocessable_entity
    end
  end

  def edit
  end

  def update
    if @post.update(post_params)
      redirect_to @post, notice: 'Post updated.'
    else
      render :edit, status: :unprocessable_entity
    end
  end

  def destroy
    @post.destroy
    redirect_to posts_path, notice: 'Post deleted.'
  end

  private

  # 3. Private methods
  def set_post
    @post = current_user.posts.find(params[:id])
  end

  def post_params
    params.expect(post: [:title, :content, :published])
  end
end

Strong Parameters (Rails 8+)

# Rails 8+ syntax with expect
def post_params
  params.expect(post: [:title, :content, tags: []])
end

# Nested attributes
def user_params
  params.expect(user: [:name, :email, profile_attributes: [:bio, :avatar]])
end

# Traditional permit (still works)
def post_params
  params.require(:post).permit(:title, :content, tags: [])
end

Quick Reference

Key Conventions

• Use redirect_to after successful changes
• Use render :action, status: :unprocessable_entity for validation failures
• Return appropriate HTTP status codes
• Keep private methods minimal