ThingsController - Typical Controller Structure

thing.rb

# For database-backed models:
class Thing < ApplicationRecord

  validates :name, presence: true  
end

# For Plain Old Ruby Object models:
class Thing
  include ActiveModel::Model
  
  attr_accessor :name, :description
  
  validates :name, presence: true
  
  # DIY `save`, `destroy`, `update` methods only if needed, and use
  # more appropriate verbs as method names if they reveal the intention
  # more clearly.
  def save
    ...
  end
  
  def destroy
    ...
  end
  
  def update
    ...
  end
end

things_controller.rb

# Pretty much the output from `rails generate scaffold Thing` with a few tweaks:
# - Replace `before_action :set_thing, only: ...` with `find_thing` (avoid Mystery Guest)
# - Specializes in serving HTML (JSON handling commented out and `respond_to` use removed.)

class ThingsController < ApplicationController

  def index
    @things = Thing.all
  end

  def show
    @thing = find_thing
  end

  def new
    @thing = Thing.new
  end

  def edit
    @thing = find_thing
  end

  def create
    @thing = Thing.new(thing_params)

    if @thing.save
      redirect_to @thing, notice: 'Thing was successfully created.'
      # render :show, status: :created, location: @thing
    else
      render :new
      # render json: @thing.errors, status: :unprocessable_entity
    end
  end

  def update
    @thing = find_thing

    if @thing.update(thing_params)
      redirect_to @thing, notice: 'Thing was successfully updated.'
      # render :show, status: :ok, location: @thing
    else
      render :edit
      # render json: @thing.errors, status: :unprocessable_entity
    end
  end

  def destroy
    @thing = find_thing

    @thing.destroy

    redirect_to things_url, notice: 'Thing was successfully destroyed.'
    # head :no_content
  end

  private

  def find_thing
    Thing.find(params[:id])
  end

  def thing_params
    params.require(:thing).permit(:name, :description)
  end

end

removed.