BaseRepository example

base_repository.rb

require 'csv'

# There are a bunch of ways of doing this class
# There's not one 'best' way, but different approaches
class BaseRepository


	# This is an initialize method that is
	# Common for 90% of the Repositories
	# It just takes a CSV file, and creates
	# @elements empty list (array)
	def initialize(csv_file)
		@elements = []
		@csv_file = csv_file
	end


	# Nothing, just return all elements, that's it
	def all
		@elements
	end


	# Take a look in the documentation, find
	# returns the object that matched with the condition
	# inside (in this case, the ID of the MEAL to be equal to the ID in
	# the method definition)
	def find(id)
		@elements.find { |el| el.id == id }
	end


	# Just add the element(meal, customer, employee, whatever)
	# To the elements array and setup the next id
	# I removed the sync from here, because it's up to the
	# child repository to find out if he wants to use it
	# That's why we can call SUPER on the CHILDREN, it will just
	# execute these 2 lines, then give the control back to you
	def add(element)
		element.id = next_id
		@elements << element
	end



	private
	# Just finding out the next_id,
	# If @elements is empty, 1
	# If @elements has (meals/customer/employee),
	# get the last ID from the item
	def next_id
		@elements.empty? ? 1 : @elements.last.id + 1
	end


	# This is a weird thing, right?
	# It's just a method that receives one argument: a CLASS itself
	# Not a string, not an array, but a class
	# So we can call .NEW on it - pretty cool, right?
	# Look, the name in the method definition is up to you
	# I decided for klass, but you can call it class_name and
	# it will work the same way
	def sync_csv(klass)
		CSV.open(@csv_file, 'wb') do |csv|
			# This line just find all instance variables and returns them as strings
			# Inside an array (['@name', '@price'])
			# We just remove the "@" from the string ([1..-1] instead of [0..-1])
			csv << klass.new.instance_variables.map { |x| x[1..-1] }
			@elements.each do |element|
				# This is tricky right?
				# YIELD is quite simple once you understand it.
				# If you use `DO` on this method
				# E.g.: `sync_csv DO |some_variable|`
				# This will call yield - and because we passed a variable to yield
				# We have access to this variable (to do whatever we want) all the
				# way up there in the children class
				# So we are just converting this yield to whatever we pass
				# INSIDE the block there in the children.


				# This will be converted to whatever you want,
				# In our case, it's ["Something", "Something", "Something"]
				# Look at the child class (MealRepository, CustomerRepository)
				csv << yield(element)
			end
		end
	end




	# Again, we receive a CLASS as an argument when we call it
	# it's just a variable name, call whatever you want
	# This method only is only used if we need to convert the rows
	# to a Ruby format
	# Like "true" to true (boolean) and "1" to 1 (integer)
	def load_csv(klass)
		csv_options = { headers: :first_row, header_converters: :symbol }

		# We dont run anything, just skip - if the file doesnt exist
		return unless File.exist?(@csv_file)

		CSV.foreach(@csv_file, csv_options) do |row|
			row[:id]    = row[:id].to_i

			# Again, if you use DO on this method
			# E.g.: `load_csv(Meal) do |some_variable|`
			# It will replace the value of yield with the value
			# inside your DO block
			# BLOCK_GIVEN? means: only run this line if we use `DO` on this
			# method
			yield(row) if block_given?
			@elements << klass.new(row)
		end
	end

end

customer_repository.rb

require_relative '../models/customer'
require_relative 'base_repository'
require 'csv'


# We are inheriting from the Base repository
# That has ALL methods that we need
# We are only overriding the ones we actually
# need to change
class CustomerRepository < BaseRepository

  def initialize(csv)
    super(csv)
    load_csv Customer
  end

  def add(element)
    super
    sync_csv Customer do |customer|
      [customer.id, customer.name, customer.address]
    end
  end
end

meal_repository.rb

require_relative "../models/meal"
require_relative 'base_repository'
require 'csv'


class MealRepository < BaseRepository

  def initialize(csv)
    super(csv)
    
    load_csv Meal do |row|
      row[:price] = row[:price].to_i
    end
  end
  
  def add(element)
    super
    sync_csv Meal do |meal| 
      [meal.id, meal.name, meal.price]
    end
  end
end