Natasha Buckham

app.rb

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+require_relative 'lib/database_connection'
+require_relative './lib/item_repository'
+require_relative './lib/order_repository'
+
+# Could refactor run method so the logic for each step is pulled out into separate methods
+
+class Application
+  def initialize(database_name, io, item_repository, order_repository)
+    DatabaseConnection.connect(database_name)
+    @io = io
+    @item_repository = item_repository
+    @order_repository = order_repository
+  end
+
+  def run
+    action_list = "1 = list all shop items\n2 = create a new item\n3 = list all orders\n4 = create a new order\n5 = quit program\n\n"
+    action = nil
+    @io.puts "\nWelcome to the shop management program!\n"
+
+    until action == "exit"
+      @io.puts "\nWhat do you want to do?\n#{action_list}"
+      action = @io.gets.chomp
+
+      case action
+        when "1"
+          items = @item_repository.all
+          items.each do |item|
+            @io.puts "\n#{item.id}. #{item.name} - unit price: #{item.price} - quantity: #{item.quantity}"
+          end
+
+        when "2"
+          item = Item.new
+          @io.puts "What is the name of the item?"
+          item.name = @io.gets.chomp
+          @io.puts "What is the price of the item?"
+          item.price = @io.gets.chomp
+          @io.puts "How many of the item will be in stock?"
+          item.quantity = @io.gets.chomp
+
+          @item_repository.create(item)
+
+          @io.puts "#{item.name} added to the database."
+
+        when "3"
+          orders = @order_repository.all
+
+          orders.each do |order|
+            @io.puts "\n#{order.id}. customer name: #{order.customer} - order date: #{order.date}\nOrder contents:\n"
+            items = @item_repository.find_by_order(order.id)
+            items.each do |item|
+              @io.puts "#{item.name} - unit price: #{item.price}\n"
+            end
+          end
+
+        when "4"
+          order = Order.new
+          @io.puts "What is the customer's name?"
+          order.customer = @io.gets.chomp
+          @io.puts "What date was the order made?"
+          order.date = @io.gets.chomp
+          @order_repository.create(order)
+          last_id = @order_repository.all.last.id
+          @created_order = @order_repository.find(last_id)
+          @io.puts "How many items do you want to add to the order?"
+          number = @io.gets.chomp.to_i
+          number.times() do
+            @io.puts "What is the id of the item you want to add?"
+            item_id = @io.gets.chomp
+            item = @item_repository.find(item_id)
+            if item.quantity == '0'
+              @io.puts "That item is out of stock. Item could not be added. Please start again."
+              @order_repository.delete(@created_order.id)
+            else
+              @created_order.add_item(item)
+              item.quantity = item.quantity.to_i - 1
+              @item_repository.update(item)
+              @io.puts "#{item.name} added to order."
+            end
+          end
+
+        when "5"
+          break
+
+        else
+        @io.puts "Invalid input. Please input a number from 1 to 5."
+      end
+    end
+  end
+end
+
+if __FILE__ == $0
+  app = Application.new(
+    'shop_manager',
+    Kernel,
+    ItemRepository.new,
+    OrderRepository.new)
+    app.run
+end

lib/database_connection.rb

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+# file: lib/database_connection.rb
+
+require 'pg'
+
+# This class is a thin "wrapper" around the
+# PG library. We'll use it in our project to interact
+# with the database using SQL.
+
+class DatabaseConnection
+  # This method connects to PostgreSQL using the
+  # PG gem. We connect to 127.0.0.1, and select
+  # the database name given in argument.
+  def self.connect(database_name)
+    @connection = PG.connect({ host: '127.0.0.1', dbname: database_name })
+  end
+
+  # This method executes an SQL query
+  # on the database, providing some optional parameters
+  # (you will learn a bit later about when to provide these parameters).
+  def self.exec_params(query, params)
+    if @connection.nil?
+      raise 'DatabaseConnection.exec_params: Cannot run a SQL query as the connection to'\
+      'the database was never opened. Did you make sure to call first the method '\
+      '`DatabaseConnection.connect` in your app.rb file (or in your tests spec_helper.rb)?'
+    end
+    @connection.exec_params(query, params)
+  end
+end

lib/item.rb

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+class Item
+  attr_accessor :id, :name, :price, :quantity
+end

lib/item_repository.rb

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+require_relative './item'
+
+class ItemRepository
+  def all
+    sql = 'SELECT id, name, price, quantity FROM items;'
+    result_set = DatabaseConnection.exec_params(sql, [])
+
+    items = []
+
+    result_set.each do |record|
+      item = Item.new
+      item.id = record['id']
+      item.name = record['name']
+      item.price = record['price']
+      item.quantity = record['quantity']
+
+      items << item
+    end
+
+    items
+  end
+
+  def find(id)
+    sql = 'SELECT id, name, price, quantity FROM items WHERE id = $1;'
+    params = [id]
+
+    result = DatabaseConnection.exec_params(sql, params)
+
+    result.each do |record|
+      item = Item.new
+      item.id = record['id']
+      item.name = record['name']
+      item.price = record['price']
+      item.quantity = record['quantity']
+
+      return item
+    end
+  end
+
+  def find_by_order(order_id)
+    sql = 'SELECT items.id, items.name, items.price, items.quantity
+    FROM items
+    JOIN items_orders ON items_orders.item_id = items.id
+    JOIN orders ON items_orders.order_id = orders.id
+    WHERE orders.id = $1;'
+    params = [order_id]
+
+    result_set = DatabaseConnection.exec_params(sql, params)
+
+    items = []
+
+    result_set.each do |record|
+      item = Item.new
+      item.id = record['id']
+      item.name = record['name']
+      item.price = record['price']
+      item.quantity = record['quantity']
+
+      items << item
+    end
+
+    items
+  end
+
+  def create(item)
+  sql = 'INSERT INTO items (name, price, quantity) VALUES ($1, $2, $3);'
+  params = [item.name, item.price, item.quantity]
+
+  DatabaseConnection.exec_params(sql, params)
+  end
+
+  def update(item) # need to update quantity when an item is added to an order
+    sql = 'UPDATE items SET quantity = $1 WHERE id = $2;'
+    params = [item.quantity, item.id]
+
+    DatabaseConnection.exec_params(sql, params)
+  end
+
+  def delete(id) # when quantity reaches zero, need to delete item from stock
+    sql = 'DELETE FROM items WHERE id = $1;'
+    params = [id]
+
+    DatabaseConnection.exec_params(sql, params)
+  end
+end

lib/order.rb

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+class Order
+  attr_accessor :id, :customer, :date
+
+  def add_item(item)
+    order_id = self.id
+    item_id = item.id
+
+    join_sql = 'INSERT INTO items_orders (item_id, order_id) VALUES ($1, $2);'
+    join_params = [item_id, order_id]
+
+    DatabaseConnection.exec_params(join_sql, join_params)
+  end
+end

lib/order_repository.rb

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+require_relative './order'
+
+class OrderRepository
+  def all
+    sql = 'SELECT id, customer, date FROM orders;'
+    result_set = DatabaseConnection.exec_params(sql, [])
+
+    orders = []
+
+    result_set.each do |record|
+      order = Order.new
+      order.id = record['id']
+      order.customer = record['customer']
+      order.date = record['date']
+
+      orders << order
+    end
+
+    orders
+  end
+
+  def find(id)
+    sql = 'SELECT id, customer, date FROM orders WHERE id = $1;'
+    params = [id]
+
+    result = DatabaseConnection.exec_params(sql, params)
+
+    result.each do |record|
+      order = Order.new
+      order.id = record['id']
+      order.customer = record['customer']
+      order.date = record['date']
+
+      return order
+    end
+  end
+
+  def create(order)
+    sql = 'INSERT INTO orders (customer, date) VALUES ($1, $2);'
+    params = [order.customer, order.date]
+
+    DatabaseConnection.exec_params(sql, params)
+  end
+
+  def delete(id)
+    sql = 'DELETE FROM orders WHERE id = $1;'
+    params = [id]
+
+    DatabaseConnection.exec_params(sql, params)
+  end
+end

recipes/items_orders.sql

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+CREATE TABLE items (
+  id SERIAL PRIMARY KEY,
+  name text,
+  price int,
+  quantity int
+);
+
+-- Create the second table.
+CREATE TABLE orders (
+  id SERIAL PRIMARY KEY,
+  customer text,
+  date date
+);
+
+-- Create the join table.
+CREATE TABLE items_orders (
+  item_id int,
+  order_id int,
+  constraint fk_item foreign key(item_id) references items(id) on delete cascade,
+  constraint fk_order foreign key(order_id) references orders(id) on delete cascade,
+  PRIMARY KEY (item_id, order_id)
+);