Coding practice

Goal: Teaching ruby to newbies

We will build a self-checkout machine used in a supermarket together.

Task 3

TODO

Checkout to the start point of Task 3

git checkout task3

Use ActiveRecord to persist data to SQLite

Requirements

Install ActiveRecord and SQLite
Setup ActiveRecod to talk to SQLite memory storage
Define database tables to save products, discounts, and purchases
Extend Product, Discount, and Purchase classes to ActiveRecord::Base
Set relationships of each tables in models
purchase_summary shows hour:minute:second applying New Zealand Timezone

store.purchase_summary() #=>
[
  ["Time","Number of Products","Cost"],
  ["17/07/2015 00:00:00",2,20.0],
  ["18/07/2015 00:00:00",1,15.99]
]

Raise an error if product and discount are not valid

Product: barcode and name should exist and cost should be bigger than 0

Discount: amount should be bigger than 0

ActiveRecord syntax

setup

Tell ruby which gems (libraries) to use (activerecord and sqlite3 gems in this case)

# create ./Gemfile to top folder and type below
source 'https://rubygems.org'

gem 'sqlite3', '1.3.10'
gem 'activerecord', '4.2.0'

install gems

# type this command on the top folder in termimal
bundle install

load active_record gem to use

require 'active_record'

setup connection to SQLite memory storage

ActiveRecord::Base.establish_connection adapter: "sqlite3", database: ":memory:"

Create database tables

More info

ActiveRecord::Schema.define do
  # create cars table with 5 fields (actually 6 in total including id)
  create_table "cars" do |t|
    t.string   "name",        limit: 255
    t.integer  "year",        limit: 4
    t.integer  "owner_id",    limit: 4
    t.decimal  "price",       precision: 8, scale: 2
    t.datetime "purchased_at"
  end
  # create table connect cars and drivers in many to many relationship
  # set {id: false} if no need direct access to this table
  create_table "cars_drivers", id: false do |t|
    t.integer  "car_id",      limit: 4
    t.integer  "driver_id",   limit: 4
  end
  create_table "drivers" do |t|
    t.string   "name",        limit: 255
  end
  create_table "ownsers" do |t|
    t.string   "name",        limit: 255
  end
end

Create Class to represent each table and setup relations

More info

class Car < ActiveRecord::Base
  has_and_belongs_to_many :drivers
  belongs_to :owner
end
class Driver < ActiveRecord::Base
  has_and_belongs_to_many :cars
end
class Owner < ActiveRecord::Base
  has_many :cars
end

Usage

Car.first.drivers # get drivers of the first car in the database through cars_drivers table

Find records

More info

# find a car having id = 1
Car.find(1)
# find a car having name = "A4"
Car.find_by(name: "A4")
# find cars having name = "A4"
Car.where(name: "A4")
Car.where("cars.name = ?", "A4")
Car.where("cars.name = :name", name: "A4")
# use relations
Car.find(1).drivers
Car.find(1).owner
Owner.find(1).cars
# find cars which owner's name = "bob"
Car.joins(:owner).where(owners: {name: "bob"})
# count records
Car.count
Car.where(name: "A4").count

Validation

More info

set validation

class Car < ActiveRecord::Base
  validates :name,  presence: true # name should exist
  validates :price, numericality: {greater_than: 0}
end

check validation

Car.new(name: "", price: 0).valid? #=> false

validation is also called in save and update methods

Car.new(name: "", price: 0).save     #=> false
Car.first.update(name: "", price: 0) #=> false

Time zone in Rails

More info

ActiveRecord saves time data to database as UTC (+0 hours). Time zone is required when we display data to the end user. Once you set time zone, time.zone methods (example: Time.zone.now) and active record's time data methods (example: Car.first.purchased_at) return the time with that time zone.

Even you set Time.zone, ruby time methods like Time.now (without 'zone') will return the time with time zone set in your OS.

Use time zone to ActiveRecord (aleady set in Rails)

ActiveRecord::Base.time_zone_aware_attributes = true

Set time zone

Time.zone = "Pacific/Auckland"

Useage

Time.zone.now          # Mon, 27 Jul 2015 19:00:19 NZST +12:00
Car.first.purchased_at # Mon, 27 Jul 2015 19:00:19 NZST +12:00

Task 2

TODO

Implement new requirements to store.rb and store_test.rb. Reading Ruby syntax will be useful to do this task.

Requirements

Receipts show costs including cents (example: apple $5.00)
Customers can purchase products which returns the receipt

store.purchase(["0001", "0002"]) #=>
apple $5.00
orange $10.00
total $15.00

Owner can view purchase summary as data array

store.purchase_summary() #=>
[
  ["Time","Number of Products","Cost"],
  ["17/07/2015",2,20.0],
  ["18/07/2015",1,15.99]
]

Owner can add discount to a product

store.add_discount("0001", 1) #=> $1 discount to product "0001"

Owner can delete discount to a product

store.delete_discount("0001") #=> delete discount to product "0001"

Extra Task: Save products, purchases, discounts to SQL database using ActiveRecord with SQLite. ActiveRecord is M in MVC from Ruby on Rails framework. We will go through how to use this library in next class

Ruby syntax

Format string

More info

"display float %.1f" % 1 #=> display float 1.0

Time

More info

Time.now            #=> 2015-07-19 20:32:52 +1200
Time.new(2015,7,19) #=> 2015-07-19 00:00:00 +1200
Time.new(2015,7,19).strftime("%Y-%m-%d") #=> "2015-07-19"

Task 1

TODO

As a tester, remove store_test.rb and recreate it from store.rb

As a developer, remove store.rb and recreate it to pass store_test.rb

As a passinate person, remove store_test.rb and store.rb and create them using TDD

Requirements

User can add an item to store

store.add_item("0001", "apple", 10) # add $10 apple with barcode 0001

User can count stored items

store.item_count() #=> 10 (10 items)

User can calculate total cost of given items

store.calculate_cost(["0001", "0001"]) #=> 20 (two apples costs $20)

User can print receipt of given items

store.print_receipt(["0001", "0001"]) #=>
apple $10
apple $10
total $20

Setup environment

Using Windows + Rubymine (not free)

Install railsinstaller from http://railsinstaller.org/en (WINDOWS RUBY 2.1)
Install Rubymine from https://www.jetbrains.com/ruby/ (Not free but students can get 1 year license)
Clone this project

Run Rubymine
Welcome page -> check out from Version Control -> Git
Fill Repository info and click clone
- Git Repository URL "https://github.com/ducktyper/countdown.git"
- Parent Directory "choose where you want to save this project in your computer"
- Directory Name "countdown"

Run test

toolbar -> click 'run' -> click 'Run' -> choose 1. All tests in countdown

Using Windows + Sublime Text (free)

Install railsinstaller from http://railsinstaller.org/en (WINDOWS RUBY 2.1)
Install Sublime Text from https://http://www.sublimetext.com
Clone this project

Open Terminal
Move to where you want to clone the project (Example: C:\Users\daniel\Desktop\projects)
git clone https://github.com/ducktyper/countdown.git

Open cloned folder from Sublime Text
Open score_test.rb file and click Ctrl-b to run test

Here is basic ruby syntax useful to this task.

Ruby Syntax

Define Class

More info

class with no argument

class Item
  def initialize()
  end
end

create with 1 argument

class Item
  def initialize(name)
  end
end

Create object

item1 = Item.new()
item2 = Item.new("apple")

Include other file

require "./item" # read file item.rb under the current folder and insert it

instance variable (start with @)

class Item
  def initialize(name)
    @name = name
  end
  def print()
    puts @name
  end
end
Item.new("apple").print() #=> "apple"

instance method

declear method

class Item
  def initialize()
  end
  def price(quantity)
    10 * quantity # result of the last line returns automatically
  end
end

call method

price = Item.new().price(5) #=> 50

Condition

if statement

if (1 == 1)
  puts "case1"
elsif (2 == 2)
  puts "case2"
else
  puts "case3"
end

switch statement

case 1
when 1
  puts "1"
when 2
  puts "2"
end

String

More info

create string

name = "apple"

append string

name = "apple"
puts name + "orange" #=> apple orange

combine strings

name = "apple"
puts "having #{name}" #=> having apple

Array

More info

create empty array

array = []

add item to array

array = []
array << "milk"

get item by index

array = ["apple", "orange"]
array[0] #=> "apple"

find index of item

array = ["apple", "orange"]
array.index("apple") #=> 0

loop through each item

array = ["apple", "orange"]
array.each do |item|
  puts item # execute this line for each item
end #=> "apple\norange"
array.each { |item| puts item } # same as above

map to create a new array with different value

array = [1,2,3]
array.map do |item|
  item * 3
end #=> [3,6,9]

Hash

More info

A Hash is a dictionary-like collection of unique keys and their values. Same as 'Dictionary' in C#, 'Object Properties' in Javascript.

create empty hash

hash = {}

add key and value pair

hash = {}
hash["key"] = "value"

get value from key

hash = {"key" => "value"}
hash["key"] #=> "value"

Symbol

More info

Symbol is like string but faster to compare equality. It is popular using Symbol as key in Hash.

Use Symbol in Hash

hash = {:name => "apple", :price => 10}

Short syntax using Symbol in Hash

hash = {name: "apple", price: 10}

Methods for array like classes

More info

Inject to compose data

# update 0 5 times (0 -> 1 -> 3 -> 6 -> 10 -> 15) and return
[1, 2, 3, 4, 5].inject(0) do |total, number|
  total + number
end #=> 15

Minitest

file name ends with "_test.rb"

basic format

require 'minitest/autorun'
describe "math" do            # 'describe' block wraps 'it' blocks
  it "can sum two numbers" do # 'it' block represents single test
    assert_equal(2, 1 + 1)    # assertion
  end
end

assertion

expected = true
actual = (1 + 1 == 2)
assert_equal(expected, actual)

Files

README.md

Latest commit

History

README.md

File metadata and controls

Coding practice

Task 3

TODO

Requirements

ActiveRecord syntax

setup

Create database tables

Create Class to represent each table and setup relations

Find records

Validation

Time zone in Rails

Task 2

TODO

Requirements

Ruby syntax

Format string

Time

Task 1

TODO

Requirements

Setup environment

Using Windows + Rubymine (not free)

Using Windows + Sublime Text (free)

Ruby Syntax

Define Class

class with no argument

create with 1 argument

Create object

Include other file

instance variable (start with @)

instance method

Condition

String

Array

Hash

Symbol

Methods for array like classes

Minitest