How to limit number of uploads by user? - ruby-on-rails

Question

relatively new to ruby on rails and I'm creating a simple Uploads model for Paperclip images to be attached and displayed. I've got that all working well, but I want to limit a current user to upload no more than 6 images at any given time.
In what file and what code would I add this? It would be quite helpful to know this for any future model I create !
I'm assuming it's quite a small bit of code but I can't see an answer anywhere online... thanks !
my UploadsController (did a simple scaffolding and paperclip setup):
class UploadsController < ApplicationController
before_action :set_upload, only: [:show, :edit, :update, :destroy]
# GET /uploads
# GET /uploads.json
def index
#uploads = Upload.all
end
# GET /uploads/1
# GET /uploads/1.json
def show
end
# GET /uploads/new
def new
#upload = current_user.uploads.build
end
# GET /uploads/1/edit
def edit
end
# POST /uploads
# POST /uploads.json
def create
#upload = current_user.uploads.build(upload_params)
respond_to do |format|
if #upload.save
format.html { redirect_to #upload, notice: 'Upload was successfully created.' }
format.json { render :show, status: :created, location: #upload }
else
format.html { render :new }
format.json { render json: #upload.errors, status: :unprocessable_entity }
end
end
end
# PATCH/PUT /uploads/1
# PATCH/PUT /uploads/1.json
def update
respond_to do |format|
if #upload.update(upload_params)
format.html { redirect_to #upload, notice: 'Upload was successfully updated.' }
format.json { render :show, status: :ok, location: #upload }
else
format.html { render :edit }
format.json { render json: #upload.errors, status: :unprocessable_entity }
end
end
end
# DELETE /uploads/1
# DELETE /uploads/1.json
def destroy
#upload.destroy
respond_to do |format|
format.html { redirect_to uploads_url, notice: 'Upload was successfully destroyed.' }
format.json { head :no_content }
end
end
private
# Use callbacks to share common setup or constraints between actions.
def set_upload
#upload = Upload.find(params[:id])
end
# Never trust parameters from the scary internet, only allow the white list through.
def upload_params
params.require(:upload).permit(:upload_title, :upload_description, :upload_datecreated, :user_id, :picture, :delete_picture)
end
end
Upload model:
class Upload < ActiveRecord::Base
belongs_to :user
has_attached_file :picture, styles: { large: "600x600#", medium: "300x300#", small: "150x150#", thumb: "50x50#" }, default_url: "/images/:style/missing.png"
validates_attachment_content_type :picture, content_type: /\Aimage\/.*\Z/
before_validation { image.clear if #delete_image }
def delete_picture
#delete_image ||= false
end
def delete_picture=(value)
#delete_image = !value.to_i.zero?
end
end

Answer 1

class Upload < ActiveRecord::Base
MAX_IMAGES = 6
validate :maximum_images
private
def count_valid_images
self.user.uploads.count
end
def maximum_images
errors.add(:base, "must have max #{MAX_IMAGES} images") if count_valid_images > MAX_IMAGES
end
end