Introduction to information systems RUBY ON RAILS dr inż. Tomasz Pieciukiewicz

Rails–web development framework for Ruby  Introduction to Rails  View and Controller in Rails  Model in Rails  Scaffolding  Plugins

Intro

Convention over configuration  Use of default settings, configuration and coding standards results in shorter,easier code  Everything may be reconfigured– but why bother?

DRY  Don’t repeat yourself  If a programmer stated a piece of information somewhere, it doesn’t have to be repeated

Command line  Important operations are executed with command line - invoked scripts, e.g.:  rails new appName – generate app skeleton  rails server – run built-in www server  rails generate controller Name –create controller class  Gem –command line tool for package downloads (apt equivalent)  Rake – Ant equivalent

Important features  MVC based  built in ORM  many utility packages  seriously reduces development time

Controllers and views

Controller  Controller class extends the Application Controller class  Class name is NameController  Class is saved to name_controller.rb in the controllers folder  controllers folder may contain subfolders -> controller hierarchy

Controller  With default routing rules each method in the controller is an action URL contains method's name  n  parameters may be passed this way:  n/param1/param2

Controller  class HelloController < ApplicationController  def index  end  def there  end

View  View is a.erb.html file with the same name, as the action using it, put in the application folder, views\controller Name subfolder .erb.html is html with embedded Ruby code

View  Ruby code is put in tags  Expression values are in tags  Like in other similar languages, Ruby codemay be used to display HTML in certainways(loops, conditional expressions)  Code should be limited to view-related  processing, business logic goes into controller and/or model

View  View has access to instance attributes of invoking controller instance  This way, we may easily pass information from controller to view

View  By default, the controller's action renders the appropriate view at the end of its execution  render method may be used to display a different view:  render(:action => :actionName) –displays view related to a specific action  render(:file => path) –displays view from a specific file

View  hrefs to to other actions may be inserted using link_to method  "actionname"%>  "controllername", :action=>"actionname%>

View and controller  Access to request parameters –using the  params array:params[:paramName]  If a form element (e.g. select) may return multiple values, its name has to end with[]

View and controller  Session variables are stored in session association array:   Access to cookies using cookies association array:  cookies[:name]={:value=>value, :expires=when}

Models

Custom implementation  Located in the models folder  Each model class defines its own methodsand attributes, handles persistence  May extend e.g. the Base class (class that implements database access)

Active Record – typical approach  Create tables in database  Configure the database.yml file (config folder)  Generate model  rails generate model modelName

Database tables  Convention over configuration  Names in plural (english rules), e.g.:  Table bikes -> class Bike  Table people -> class Person  Primary key should be named id and be integer. Autoincrement is a good idea here ;)  Foreign keys – name of the foreign table in singular+"_id", eg person_id, bike_id,

Active Record classes  Simple Active Record class:  class Purchase < ActiveRecord::Base  end  This class provides access to all tuple's columns (read and write), searching etc.  We have to define relations with other tables and operations

Active Record  Record creation  Using new method to create object and save to save it to DB:  b = Book.new :title=>"sth", :author=>"auth"  b.save  Using create method (w/o save):  Book.create :title=>"sth",:author=>"auth"

Active Record  Record deletion  Database-level  delete(id)  delete 552  delete_all [condition]  Book.delete_all (['year<?',2007])  Object-level (recommended) - destroy  destroy_all [condition]  destroy_all ['alive=0']

Active Record  Updates  save – saves all changes to the database  CurrentBook.save  update_attribute – updates a specified attribute  CurrentBook.update_attribute :title=>'RoR'  update_attributes – updates a specified set of attributes  CurrentBook.update_attributes {:title=>'RoR',  :year=>2007}  update_all – update to a large group of records, change and conditions have to be specified  Book.update_all "price=1.22*price", :year=>2008

Active Record  Searching  within model, using SQL  find_by_sql "sql query"  User.find_by_sql "SELECT * FROM users"  count_by_sql "sql query"  User.count_by_sql "SELECT COUNT(*) FROM  users"

Active Record  Searching  outside model, using SQL  connection.select_all "sql query"  connection.select_one "sql query"  connection.execute "sql query" (does not have to  be search)

Active Record  Searching  using Active Record methods  Model.find id – using primary key as parameter  Book.find 548  Model.find :conditions=>['column=?',value]  Book.find :conditions => ['id=?',2]  Book.find :conditions => {:id=>2}  Model.find_by_xxx and Model.find_all_by_xxx –  created automatically for all columns, xxx is the name of  the column  Book.find_by_id 222  Book.find_by_id [1,345,1112]  Book.find_all_by_title "Bible"

Active Record  Relationships  belongs_to – n-side of 1:n relationship (n=1  or *)  has_one – 1-side of 1:1 relationship  has_many – 1-side of 1:* relationship  has_and_belongs_to_many – relationship *:*,  a table named table1_table2 must exist – will be used to estabilish *:* relationship

Active Record  Basic data validation  validates_presence_of :column - check if column contains data  guess:  validates_acceptance_of  validates_associated  validates_confirmation_of  validates_each  validates_exclusion_of  validates_format_of  validates_inclusion_of  validates_length_of  validates_numericality_of  validates_presence_of  validates_size_of  validates_uniqueness_of

Active Record  Data validation using methods:  class Comment < ActiveRecord::Base  validate :must_be_friends  def must_be_friends  errors.add_to_base("Must be friends \  to leave a comment") unless \  commenter.friend_of?(commentee)  end

Active Record  classBook < ActiveRecord::Base  has_and_belongs_to_many: authors  has_many:editions  validates_presence_of :title, :price  end

Active Record  SQL Injection protection  Never:  User.all :conditions => "login='#{login}' AND passwd='#{passwd}'"  Always:  User.all :conditions => ["login=? AND passwd=?", login, passwd]

Form helpers

form_for  form_for - used for HTML forms based upon ActiveRecord objects  <%=  :url => { :controller => "controller", :action => "action" },  :html => { :multipart => true, :method => :put }) do |f| %> ... 

form_for  :class - (required) name of model object for fields. Input fields will be prefixed with this - (optional) ActiveRecord model object, if named differently than class  :html - (optional) hash of HTML attributes for tag  :method - (optional) HTTP method to use  :url - url to post the form to  |f| - form object, used to create fields

Input field helpers  Multiple helpers, each used to create different type of form field  f.error_messages_for  f.check_box  f.file_field  f.hidden_field  f.label  f.password_field  f.radio_button  f.text_area  f.text_field  Description of parameters can be found here: 

More helpers  There are also helpers used to create select fields from collections:  pers/FormOptionsHelper.html create date and time input fields  pers/DateHelper.html and many others

Scaffolding

 Scaffolding allows us to quickly and easily create a simple CRUD application  It also generates Ruby code required to create a database following a certain specification  The DB schema may be migrated to a DB server by using the Rake tool

Scaffolding  Creating scaffolding:  rails generate scaffold ModelName column:type, column:type …  rails generate scaffold Movie title:string description:text one_sheet_url:string  Migrating database  rake db:migrate

Thank you for your attention QUESTIONS?