�ݺ�ߣ

Learning to Code for
Startup MVP

Presented by Henry Shi

Agenda �C Wednesday November 7

1. Review of Last Session

2. Ruby Basics
o Syntax and semantics
o Practice makes perfect

1. Rails Models (but no Bottles)
o ORM and SQL introduction
o Migrations
o Making the User model
o Signup/Signin/Signout

Prework �C Setup
? Windows (not recommended if possible):
o http://railsinstaller.org/
o Use Sublime Text for your text editor
? OSX:
o http://railsinstaller.org/
o This includes osx-gcc-installer (200mb)
? Linux:
o http://blog.sudobits.com/2012/05/02/how-to-install-
ruby-on-rails-in-ubuntu-12-04-lts/

Prework - Git
Install git if not already included:
http://www.git-scm.com/book/en/Getting-
Started-Installing-Git

Configure Git:
git config --global user.name "Your Name��
git config --global user.email
your.email@example.com

Review of Last Session

1. The Web and How it Works

2. Git/Github

3. Rails and Ruby

4. Heroku

GIT/GITHUB
? What is GIT?
? Distributed Version Control System (DVCS)
? Why should I care?
o Never lose data or accidentally overwrite, delete files
o Collaborate with peers anywhere and stay in sync
automatically (no more _v1, _v2, _final, _final_final��)
o Compare and track changes over time, and easily
revert changes
o Deploy code to real web

Rails
? Ruby on Rails is an open-source web
framework that?s optimized for programmer
happiness and sustainable productivity.

? It lets you write beautiful code by favoring
convention over configuration.

? 80/20 Rule =>great for Startup MVP

Heroku
What is Heroku?
?a hosted platform built specifically for
deploying Rails and other web applications in
1 command
?Best thing since sliced bread

Ruby �C Programmer��s Best Friend
? Ruby is a dynamic, open source
programming language with a focus on
simplicity and productivity. It has an
elegant syntax that is natural to read and
easy to write.

? We will only cover the necessary syntax
needed to create a rails app
? Thankfully, its not a lot ?

Interactive Ruby Shell
? For the following slides, you should follow
along with the Interactive Ruby Shell (irb)

? Open a terminal, type irb and press enter

Ruby - Strings
? Characters (letters, digits, punctuation)
surrounded by quotes
food = "chunky bacon"
puts "I'm hungry for, #{food}!"
>> "I'm hungry for, chunky bacon!"

? Can perform operations on strings,
concatenation, length, empty, etc
��Hello�� + ��World��
>> ��Hello World"
��Henry��.empty?
>> false

Ruby - Numbers
? Self Explanatory
123.class (123.0).class
>> Fixnum >> Float

? Can add different types of numbers directly

Ruby - Symbols
? Characters (letters, digits, punctuation)
preceded by colon (:)
food = :hello
:asf3fasdf.class
>> Symbol

? Lightweight strings
? immutable

Ruby - Array
? List surrounded by square brace and
separated by commas, zero indexed
a = [1, 2, 3]
b = ('a'..'e').to_a # ["a", "b", "c", "d", "e"]
c = %w[foo bar baz quux] # ["foo", "bar", "baz", "quux"]
d = "foo bar baz".split # ["foo", "bar", "baz"]
a[0] # 3

? Can perform operations on arrays, add,
remove, reverse etc
a.push(��hello��) # [1, 2, 3, ��hello��]
a << ��world�� # [1, 2, 3, ��hello��, ��world��]
a = a.reverse # [��world��, ��hello��, 3, 2, 1]
a.delete(��hello��) # [��world��, 3, 2, 1]

Ruby - Hash
? Hash is a dictionary surrounded by curly braces
? Dictionaries match words with their de?nitions
my_var = {:sup => "dog", :foo => "bar"}
my_var[:foo]
>> "bar��
my_var[:nk] = ��new�� # {foo : "bar��, nk: ��new�� , sup : "dog" }

? New (better) hash notation in Ruby 1.9+
{sup : "dog", foo : "bar"}.class #Ruby 1.9+
>> Hash

? Important for passing optional params (can omit braces if
hash is last argument)

Ruby �C Methods (Functions)
? Function that performs some operations when
called and returns something when done

? Implicitly returns last expression in method
? Use Ruby poetry style:
o a.should(be() >= 7) #bad
o a.should be >= 7

Ruby �C Blocks
? Block of Code surrounded by curly braces
2.times { puts "hello"} 2.times do
>> "hello" puts "hello��
>> "hello" end

? Can use Do and end to indicate block as well
? Can take arguments
o variables surrounded by pipe (|)
2.times do |i|
puts "hello {#i}��
end
>> "hello 0"
>> "hello 1"

Ruby �C Blocks (Advanced Only)
? Blocks are closures: they carry their
environment around with them
? Block are anonymous �� functions
? Examples compared to scheme:
o (map '(lambda (x) (+ x 2)) mylist )

o mylist.map { |x| x+2 }
(map
'(lambda (x) (+ x 2))
(filter '(lambda (x) (even? x)) mylist))

mylist.select {|x| x.even?}.map {|x| x+2 }

? Try this: ('a'..'z').to_a.shuffle[0..7].join

Ruby �C Blocks, Methods, Hashes

def list_hash(options = {:default => "foo"})
options.each do |key, value|

puts "key '#{key}' points to '#{value}'"
end
end

list_hash override : "bar")
>> "key 'override' points to 'bar'"

list_hash multiple : "values", can : "be_passed")

>> "key 'multiple' points to 'values'"

>> "key 'can' points to 'be_passed'"

Ruby �C Hashes in Rails
? Used heavily as parameters

Ruby �C Classes and Objects
? Ruby, like many object-oriented languages,
uses classes to organize methods; these
classes are then instantiated to create objects

? Most common uses will be in Models and
Controllers

? attribute accessors (attr_accessor) corresponding to a user?s name and
email address.
? This creates ��getter�� and ��setter�� methods that allow us to retrieve (get)
and assign (set) @name and @email instance variables

Ruby Class and Object Example

? Save the above code into a file called example_user.rb
? Run the following in irb

(Advanced Only)
class SavingsAccount < Account # inheritance
# constructor used when SavingsAccount.new(...) called
def initialize(starting_balance=0) # optional argument
@balance = starting_balance
end
def balance # instance method
@balance # instance var: visible only to this object
end
def balance=(new_amount) # note method name: like setter
@balance = new_amount
end
def deposit(amount)
@balance += amount
end
@@bank_name = "MyBank.com" # class (static) variable
# A class method
def self.bank_name # note difference in method def
@@bank_name
end
# or: def SavingsAccount.bank_name ; @@bank_name ; end
end

Ruby �C Objects and Method Calls
(Advanced Only)
?? Even lowly integers and nil are true objects:
57.methods
57.heinz_varieties
nil.respond_to?(:to_s) "
?? Rewrite each of these as calls to send:"
�C? Example: my_str.length => my_str.send(:length)
1 + 2 1.send(:+, 2)
my_array[4] my_array.send(:[], 4)
my_array[3] = "foo" my_array.send(:[]=, 3,"foo")
if (x == 3) .... if (x.send(:==, 3)) ...
my_func(z)
self.send(:my_func, z)

?? When you are calling a method, you are actually sending
a method call to the receiver object, which responds

Ruby �C Method Calls (Advanced
Only)
?? Every operation is a method call
y = [1,2]
y = y + ["foo",:bar] # => [1,2,"foo",:bar]
y << 5 # => [1,2,"foo",:bar,5]
y << [6,7] # => [1,2,"foo",:bar,5,[6,7]]
?? Remember! These are nearly all instance methods of Array
��not language operators!"
?? So 5+3, "a"+"b", and [a,b]+[b,c] are all different
methods named '+'"
�C?Numeric#+, String#+, and Array#+, to be speci?c"

??a.b means: call method b on object a
�C? is the receiver to which you send the method call,
a
assuming a will respond to that method"

Ruby �C Practice
? Tryruby.org (code in ruby on your browser
and work through free exercises)

? Read Section 4.1 to 4.5 of Ruby on Rails
Tutorial by Michael Hartl

Rails - Models

We will focus on Models in this section

But First, we must understand the underlying
datastore that actually stores the data

Databases, Tables, SQL

Rails �C Database backed Models

? Store and access massive amounts of data
? Table
o Columns (name, type, modifier)
o Rows

Table:Users

SQL

? Structured Query Language
o A way to talk to databases
? Operations (CRUD)
o Create
o Read (Query)
o Update
o Delete
o Schema creation and modification
SELECT *
FROM Book
WHERE price > 100.00
ORDER BY title;

Rails �C Object Relational Mapping

? Maps database backend to ruby objects
? ActiveRecord (Rail?s Default ORM)
>> userVariable = User.where(name: "Bob")
Generates:
SELECT "users".* FROM "users"
WHERE (name = 'bob')

>> userVariable.name
=> Bob

Rails �C Object Relational Mapping

>> userVariable = User.where(name: "Bob")

models/user.rb
class User < ActiveRecord::Base
attr_accesor :name, :email
end

? Plural of Model name is table name (User -> users)
? Subclassing from ActiveRecord::Base ��Connects�� a model to
the database
o Provides CRUD operations on the model
o Database table column names are getters & setters for model attributes
o Model attributes automagically defined from the database table columns

Rails �C Creating Users

? We could start from scratch and create all
aspects of the Users models from scratch, but
that wouldn?t be in the philosophy of an MVP

? What additional functions might a user model
need?
o Registration
o Log in/Log out (sessions)
o Reset/Lost Password
o Email confirmations
o Invitations to friends

Rails �C Creating Users - Devise

? We will use the awesome Gem: Devise
? Gems are packages/libraries for your rails project
? Before coding, always see if a gem exists at
The Rails Toolbox

Rails - Devise
? Create a new rails app
o rails new MiniTwitter
? Open Gemfile (from last class)
? Add the line:
Gem ��devise��, ��2.1.0��
? Run Bundle install from the console
? Install Devise by typing in the console:
rails generate devise:install
? Generate the user by typing in the console:
rails generate devise User
? Run the migration by typing in the console:
Bundle exec rake db:migrate

Rails �C Devise
? You may seem some hints/warnings:

Rails �C Devise
? Go to http://localhost:3000/users/sign_up to see Devise
in action!

? Sign up a fake user account and now try to log in at
http://localhost:3000/users/sign_in
? Rails never shows or stores passwords in plaintext

Rails �C Devise
? What did we just do?
o rails generate devise User

o Focus on Migration and User Model

Rails �C Migrations
? Create data structure in your database
? Set a database?s schema incrementally
o Consistent across multiple machines (no conflicts)
o Easy to upgrade, rollback, track changes, etc

? Migration is automatically created every time
you create a model

? Open db/migrate/[timestamp]_devise_create_users.rb

? Creates a table named
Users

? Adds Columns:
o Email
o Encrypted_password
o Etc, etc
o T.timestamps creates the
columns created_at and
updated_at autmagically
o Can pass parameters to
columns, default values,
nullable, etc

? Adds Indices:
o Ensures uniqueness
o Faster searching
o Index on email

? Active Record Maps ruby objects to database
? User.email

? Database looks like:

? Same as what was specified in the migration

? Run a migration
>> bundle exec rake db:migrate

? Rollback (undo) a migration
>> bundle exec rake db:rollback

rails generate migration AddNameToUsers name:string

? Creates a migration automagically on the users table
because we followed naming conventions
o AddXXXToYYY followed by column name and type

? More info: http://guides.rubyonrails.org/migrations.html

Rails �C Models
? Open app/models/user.rb

? Attr_accessible is important for preventing mass
assignment vulnerability
? Notice we don?t have any attributes explicitly defined
from the database (ORM maps attributes implicitly in
Rails? Activerecord)
o Can remind ourselves of the database columns using ?annotate? gem

Rails �C Attributes
? Open app/models/user.rb

? Can add methods to the user model
def unchanged_duration
updated_at �C Time.now

end
- Duration in which the user was not modified

Rails �C Models- Validations
? Check your parameters before save
? Provided by ActiveModel
class Person < ActiveRecord::Base
validates :title, :presence => true
end

bob = Person.create(title: nil)
>> bob.valid?
=> false
>> bob.save
=> false

Rails �C Models- Validations
? Rails? built in validation
:acceptance => Boolean.
:confirmation => Boolean.
:exclusion => { :in => Enumerable }.
:inclusion => { :in => Enumerable }.
:format => { :with => Regexp, :on => :create }.
:length => { :maximum => Fixnum }.
:numericality => Boolean.
:presence => Boolean.
:uniqueness => Boolean.

? Can also write your own validations
class User < ActiveRecord::Base
validate :my_custom_validation
private
def my_custom_validation
self.errors.add(:coolness, "bad") unless self.cool == ��supercool��
end
end

Rails �C Models and Migrations
Exercises
? Create a migration to add first_name and
last_name to the User table
? Add validation for user?s email, first_name and
last_name such that they must be present
? Make a method full_name on user object to
retrieve user?s full name by concatenating first
and last name

Rails - Models
? Further Reading
Ruby on Rails Tutorial �C Michael Hartl
Section 6.1 �C 6.2 (6.3 optional)

Git Commit
git init
git add .
git commit �Cm ��Initial Commit of MiniTwitter��
(optional) git remote add origin
git@github.com:<username>/first_app.git
(optional)git push �Cu origin master

Heroku �C New MiniTwitter App
? Sign up for Heroku (it?s Free!) http://api.heroku.com/signup

? Install the Heroku Toolbelt https://toolbelt.heroku.com/

? Heroku login
? Heroku create
o This will create a heroku app and tell you the url of
your app
? Git push heroku master
o This?ll deploy your code to Heroku. Let it do its magic!
? Heroku run rake db:migrate
? Heroku open ?

Next Time��
? Exploring Rails deeper
? More about Controllers and Views
? Building toward our Twitter app posts,
friends, followers, feeds, etc
? Stay Tuned��.

? Thanks!

Rails - Appendix
? If we have time��

Rails �C Models - Create

??Must call save or save! on an AR model
instance to actually save changes to DB"
�C? version is �Ddangerous��: throws exception if
'!'
operation fails"
�C?create just combines new and save

??Once created, object acquires a primary key
(id column in every AR model table)"
�C? x.id is nil or x.new_record? is true, x
if
has never been saved"
�C?These behaviors inherited from ActiveRecord::
Base��not true of Ruby objects in general"

Rails �C Models - Read

??Class method where selects objects based on
attributes
Movie.where("rating='PG��)
Movie.where('release_date < :cutoff and
rating = :rating',
:rating => 'PG', :cutoff => 1.year.ago)
Movie.where("rating=#{rating}") # BAD IDEA!
??Can be chained together ef?ciently
kiddie = Movie.where("rating='G')

old_kids_films =
kiddie.where "release_date < ?",

Rails �C Models - Read

??Find Models by id
Movie.find(3) #exception if not found
Movie.find_by_id(3) # nil if not found

??Dynamic attribute-based ?nders using

Movie.find_all_by_rating('PG')
Movie.find_by_rating('PG')
Movie.find_by_rating!('PG')

Rails �C Models - Delete

??Note! destroy is an instance method?
m = Movie.find_by_name('The Help')
m.destroy
??There?s alsodelete, which doesn?t trigger
lifecycle callbacks we?ll discuss later (so,
avoid it)"
??Once an AR object is destroyed, you can
access but not modify in-memory object?
m.title = 'Help'

�ݺ�ߣ

Code for Startup MVP (Ruby on Rails) Session 2

Convert to study materialsBETA

More Related Content

Code for Startup MVP (Ruby on Rails) Session 2

Editor's Notes