Validations.rb

class AuthorsController < ApplicationController

  def create
    @author = Author.new(author_params)
    if @author.valid?
       @author.save
       redirect_to author_path(@author)
    else
      render :new
    end
  end
  
  class Author < ActiveRecord::Base
    validates :name, presence: true
  validates :email, uniqueness: true
end
  --------------------------------------------------------
class PostsController < ApplicationController
  before_action :set_post!, only: [:show, :edit, :update]

  def show
  end

  def edit
  end

  def update
    @post.update(post_params)
    if @post.valid?
      @post.save
    redirect_to post_path(@post)
    else
      render :edit
    end
  end
  
  private

  def post_params
    params.permit(:category, :content, :title)
  end

  def set_post!
    @post = Post.find(params[:id])
  end
end

  class Post < ActiveRecord::Base
    validates :title, presence: true
    validates :category, inclusion: { in: %w(Fiction Non-Fiction) }
    validates :content, length: { minimum: 100 }
end
  ---------------------------------------------------