Rake task to update records - ruby-on-rails

Question

I am doing a rake task that is scrapping a website in order to find concerts:
lib/tasks/my_task.rake
task :find_concerts => :environment do
doc = Nokogiri::HTML(open(url))
data = doc.search('#dateconcert table')
data = data.css('.jaunec' ).map { |tr| tr.css('td').map(&:text) } + doc.css('.jaunef' ).map { |tr| tr.css('td').map(&:text) }
data.each do |concert|
c = Concert.new
c.date = concert[0]
c.city = concert[1]
c.save
end
end
What I want
I want to get an alert when a new concert is added ( on the website I am scrapping), so the tasks will be run everyday.
My problem
I want my Concerts list to be updated if there is a new record...
With the task I wrote it finds again the records that are already stored and duplicated them...
I only want the new records that could be found...
In the end I would like to compare what is new between the two last tasks in order to send an alert if something new was found.
EDIT
This is what data returns
[
["03 Décembre 2017", "PONT L\u0092ABBE (29) | Centre Culturel Le Triskell "],
["26 Janvier 2018", "MONTPELLIER (34) | Le Jam "],
["17 Février 2018", "BLOIS (41) | All That Jazz / Les Lobis "],
["22 Mars 2018", "MOISSAC (82) | Hall de Paris "],
["24 Mars 2018", "LAX (Baraqueville) (12) | Festival Lax'N Blues LAX\u0092N "],
["08 Décembre 2017", "ECHANGE CULTUREL CAMEROUN (0) | au 18 décembre 2017 - Organisation tournée MFR "],
["27 Janvier 2018", "LE THOR (84) | Le Sonograf "],
["16 Mars 2018", "CHAUMONT (52) | Le Nouveau Relax "],
["23 Mars 2018", "AUCH (32) | Le Cri'Art "]
]

Answer 1

I found a solution that may need some refactoring, though.
So I created two tasks,
find_concerts that will be run manually for the first scrap
update_concerts that will be run every day
task
require "nokogiri"
require "open-uri"
require "date"
require "time"
namespace :scrap do
desc "This get MM concerts"
url = "http://mountain-men.fr/concerts/"
doc = Nokogiri::HTML(open(url))
data = doc.search('#dateconcert table')
data = data.css('.jaunec' ).map { |tr| tr.css('td').map(&:text) } + doc.css('.jaunef' ).map { |tr| tr.css('td').map(&:text) }
task :find_concerts => :environment do
data.each do |concert|
c = Concert.create
c.date = concert[0]
c.city = concert[1]
c.save
end
end
task :update_concerts => :environment do
existing_date = Concert.all.map { |c| [c.date, c.city] }
data.each do |concert|
c = Concert.create
c.date = concert[0]
c.city = concert[1]
c.save unless existing_date.include?([concert[0], concert[1]])
end
Concert.where(city: nil, date: nil).destroy_all
end
end

Answer 2

I am not sure if I understand you correctly, but what you need to do is to check if it exists and other wise create.
I would do some thing like this.
task :find_concerts => :environment do
doc = Nokogiri::HTML(open(url))
data = doc.search('#dateconcert table')
data = data.css('.jaunec' ).map { |tr| tr.css('td').map(&:text) } + doc.css('.jaunef' ).map { |tr| tr.css('td').map(&:text) }
data.each do |concert|
Concert.where(data: concert[0], city: concert[1]).first_or_create
end
end
Now you only create if it doesn't exist. Then when you create one you can set a hook.
class Concern
after_create :send_notification
def send_notification
# send email here
end
end