Nested/Top level resource controller sharing

posts_controller.rb

class PostsController < ApplicationController
  before_action :find_post, only: [:show, :edit, :update, :destroy]
  before_action :find_posts, only: [:index]

  def index
  end

  def show
  end

  def edit
  end

  def update
  end

  def create
  end

  def destroy
  end

  private

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

  def find_posts
    if params[:user_id]
      @posts = user.posts
    else
      @posts = Post.all
    end
  end

  def user
    user = User.find(params[:user_id])
  end
end