Rapid Application Development
COSC2675 2021 Week 6
A/Prof. Andy Song andy.song@rmit.edu.au
Last Week
• Rails Basics
• Rails philosophy
• Understand layouts **
• Adding images
• The layout method
• Template working with a layout
• Action Pack
• Model
• Controller
• Workingwithasimplewebform
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Connect to a DB through a model
• Create a model $ rails generate model entry
Running via Spring preloader in process 11245
invoke active_record
create db/migrate/[Time Stamp]_create_entries.rb create app/models/entry.rb
invoke test_unit
create test/models/entry_test.rb
create test/fixtures/entries.yml
• Contentofdb/migrate/[TimeStamp]_create_entries.rb:
class CreateEntries < ActiveRecord::Migration[5.2] def change end end end create_table :entries do |t| t.timestamps #what is this? A/Prof. Andy Song RMIT University 2021 3 The migrate rb • Atablewithpluralformofthemodelnameiscreated • Sotablebooksformodelbook,entriesforentry,micefor mouse, waters for water, sheep for sheep, gooses for goose, men for man, wolves for wolf, oxen for ox, children for child. • Methodchangereplacedself.upandself.downforundo. • Add one line: class CreateEntries < ActiveRecord::Migration[5.0] def change create_table :entries do |t| t.string :name t.timestamps end end end • Thislineistocreateacolumnofstringtostorenames. A/Prof. Andy Song RMIT University 2021 4 Migration • Tomakethelastchangetakeeffect,run$railsdb:migrate • Migrations are a convenient way to change your database schema over time. • EachmigrationcanbeconsideredasanewversionoftheDB • Aschemastartsoffwithnothinginit. • Eachmigrationmodifiesittoaddorremovetables,columns or entries. • It is managed by ActiveRecord which controls the versions. • You can $ rails db:migrate:redo STEP=3 $ rails db:rollback STEP=3 $ rails db:migarte VERSION=20210412120000 A/Prof. Andy Song RMIT University 2021 5 The skinny model • Open app/models/entry.rb, we see simply class Entry < ApplicationRecord end • BeforeRails5.0,amodelisadirectsubclassofActiveRecord. • Now it is through ApplicationRecord, open app/models/application_record.rb class ApplicationRecord < ActiveRecord::Base self.abstract_class = true end • It tries to be an abstract class although Ruby does not have abstract method and class in its syntax. A/Prof. Andy Song RMIT University 2021 6 The controller • Edit the controller app/controllers/entries_controller.rb class EntriesController < ApplicationController def sign_in @name = params[:visitor_name] @entry = Entry.create({:name => @name})
end
• Thislineeffectivelydoesthreetasksforeachentry @entry = Entry.new
@entry.name = @name # @name is from the form
@entry.save
• Name@entryisnotspecial,canbe@data,@info,@fooetc.
• The new version is better as its avoids empty entries and read all entries.
unless @name.blank?
@entry = Entry.create({:name => @name})
end
@entries = Entry.all
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•
Then the view
Edit the view: app/views/entries/sign_in.html.erb

Hello <%= @name %>

<%= form_tag action: 'sign_in' do %>

Enter your name:
<%= text_field_tag 'visitor_name', @name %>

<%= submit_tag 'Sign in' %>
<% end %>

There are <%= @entries.size %> previous visitors

<% @entries.each do |entry| %>
• <%= entry.name %>

<% end %>

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Now you should see
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Take a look at the console
Started POST “/entries/sign_in” for [IP] at [TimeStamp] Processing by EntriesController#sign_in as HTML
Parameters: {“utf8″=>”􏰀”, “authenticity_token”=>”pw..[cut]…==”, “visitor_name”=>”Louise”, “commit”=>”Sign in”}
(0.1ms) begin transaction
SQL (1.1ms) INSERT INTO “entries” (“name”, “created_at”, “updated_at”) VALUES (?, ?, ?) [[“name”, “Louise”], [“created_at”, [TimeStamp] UTC], [“updated_at”, [TimeStamp] UTC]]
(15.0ms) commit transaction
Rendering entries/sign_in.html.erb within layouts/application
(0.3ms) SELECT COUNT(*) FROM “entries”
Entry Load (0.2ms) SELECT “entries”.* FROM “entries”
Rendered entries/sign_in.html.erb within layouts/application (153.6ms)
Completed 200 OK in 196ms (Views: 175.3ms | ActiveRecord: 16.8ms)
Rails is working hard behind the scene!
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Model Methods
• Entry.all, Entry.find(1).id
• Entry.first, Entry.last.name
• Entry.where(name: “Alex”)
• Entry.limit 3, Entry.limt(3).offset(2)
• Entry.order(:name) # and many DB query methods!
• The Rails documentation also has some http://guides.rubyonrails.org/active_record_querying.html
• ThesemethodsarefromActiveRecord.Seedetailsofthese methods on Rails API: api.rubyonrails.org
• These methods can also be called in Rails console (>rails c)!
>>Entry.find(1)
Entry Load (0.3ms) SELECT “entries”.* FROM “entries” WHERE
“entries”.”id” = ? LIMIT ? [[“id”, 1], [“LIMIT”, 1]]
=> #
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Scaffolding a model
• ScaffoldingisoneofthemaincontributingfactorsforrapidRails development.
• Let us try that on a new guest book application, say guestbook_2 $ rails generate scaffold Person name:string
$ rails generate controller entries sign_in [no scaffolding]
• Itgeneratesscaffolding,aroundmodelPersonwithoneattribute
name. Note the table name is people not persons.
• Try to view it on localhost:3000/people What do you see?
• Tryagainafterrunning$railsdb:migrate A/Prof. Andy Song RMIT University 2021
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What happened in scaffolding
• ScaffoldingallowsRailscreatealistofcomponents − a model with tests
− a data migration to establish the tables for the model − a new route to map user requests to the controller
− a controller to connect different components and pass data − four views (index, edit, show and new) and a partial form − tests for the controller
− an empty file for helper methods
− a CoffeeScript file for scripting the pages − Stylesheets for all of those views
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What happened in scaffolding
• config/routes.rb
Rails.application.routes.draw do
resources :people
end
• Not much in model app/models/person.rb class Person < ApplicationRecord end • 70+ lines added automatically to the controller app/controllers/people_controller.rb • The view is a bit complicated. A/Prof. Andy Song RMIT University 2021 14 Interacting with the site Notice the URL of each page? A/Prof. Andy Song RMIT University 2021 15 RESTful Rails • TheURLsaremeaningful: .../people/edit .../people/new .../people, .../people/1, .../people/4 • The actions are visible through these URLs • You can bookmark a data resource say .../people/4 or an action .../people/2/edit • Adminscanmanagewebtrafficwithoutworryingabout disrupting the application. • AneatfitwithRails’MVCarchitecture. • EasiertobehaveRESTfully. A/Prof. Andy Song RMIT University 2021 16 REST • REpresentational State Transfer, an architecture defined by Roy Fielding in his 2000 PhD thesis at UC Irvine. • Allows access text-based web resources using a uniform and pre- defined set of stateless operations. • Does not create new techniques. • Based on HTTP request, GET = read, POST = write, DELETE = destroy, PUT = update etc. • Supports CRUD (create, read, update, destroy) which are common persistent resource operations, often seen in DB, Web, Files. • Simpler than SOAP (Simple Object Access Protocol, XML based) and WSDL ( Web Services Description Language, XML based) • Other properties: good scalability, performance, visibility, portability, modifiability, reliability. A/Prof. Andy Song RMIT University 2021 17 RESTful controller • Requires a shift in the way developers think about controllers and writing web applications. • Controllers can be verbs. Each controller implements the same verbs. • The controller becomes a standardized connection to data model. • URLs connect the client to a resource (noun) on the server in predictable ways. • Based on HTTP request, GET = read, POST = write, DELETE = destroy, PUT = update etc. • ItisnotonlyforHTML,butcanbeusedonresourcesfor JSON, Ajax. A/Prof. Andy Song RMIT University 2021 18 RESTful Routes • Remember what is in config/routes resources :people • Ifwerunthiscommand$railsroutes Prefix Verb people GET URI Pattern Controller#Action people#index people#create people#new people#edit people#show people#update people#update people#destroy new_person GET edit_person GET person GET /people/new(.:format) /people/:id/edit(.:format) /people/:id(.:format) /people(.:format) POST /people(.:format) PATCH /people/:id(.:format) PUT /people/:id(.:format) DELETE /people/:id(.:format) • ResourcesgiveasetofRESTfulURLs. • HTTP requests are mapped to actions. Meaning a URL such as GET /people/1/edit is processed by people#edit A/Prof. Andy Song RMIT University 2021 19 RESTful Routes (Learning Rails 5, Mark Locklear Eric Gruber) 20 A/Prof. Andy Song RMIT University 2021 Can work on JSON files (Learning Rails 5, Mark Locklear Eric Gruber) A/Prof. Andy Song RMIT University 2021 21 Can work on JSON files • You can try in a browser localhost:3000/people.json If we run this command $ rails routes • TheoutputofJSONfilescanbeviewedatthebrowser [{"id":1,"name":"Alexei","created_at":”[TimeStamp]", "updated_at":"[TimeStamp]","url":" localhost:3000/people/1.json"}, {"id":2,"name":"Ali","created_at":"[TimeStamp]", "updated_at":"[TimeStamp]","url":" localhost:3000/people/2.json"}, {"id”:4,"name":"Louise","created_at":"[TimeStamp]", "updated_at":"[TimeStamp]","url":" localhost:3000/people/4.json"}] • HTTP requests are mapped to actions. Meaning a URL such as GET /people/1/edit is processed by people#edit A/Prof. Andy Song RMIT University 2021 22 Specify a layout A/Prof. Andy Song RMIT University 2021 23 A/Prof. Andy Song RMIT University 2021 24 RESTful Methods • before_action :set_person, only: [:show, :edit, :update, :destroy] • The private callback set_person • The new method does not touch the database, only in memory. • The controller simply pass the model to the view new.html.erb, without worrying about the schema etc. • Person.new(person_params) is another callback • respond_to method is from ActionController, allows responses in various formats on the same data. A/Prof. Andy Song RMIT University 2021 25 Multiple Tables • Working with multiple tables is made easy by Rails. • Every model maps to a table. • The relationships between tables are managed as relationships between models. • Scaffoldingwillbehelpful.Howevertherearequitesome coding need to done manually. • Thetaskwillbemuchmoredifficultifyouareretrofittingan existing database (not generated by Rails) rather than creating a fresh new database in Rails. A/Prof. Andy Song RMIT University 2021 26 A Students Application • Create a new application called students : $ rails generate scaffold student given_name:string middle_name:string family_name:string date_of_birth:date grade_point_average:decimal start_date:date $ rails generate scaffold award name:string year:integer student_id:integer Two models have been created. Rails doesn’t know they are connected yet. Model award has a student_id field. A/Prof. Andy Song RMIT University 2021 27 A Students Application • Open app/models/student.rb and add # a student can have many awards has_many :awards • Open app/models/award.rb and add # every award is linked to a student, through student_id belongs_to :student • has_many and belongs_to are just two methods • Theyspecifytheassociationbetweenmodels • Similar methods include: has_one has_and_belongs_to_many A/Prof. Andy Song RMIT University 2021 28 Association methods • Detailsofhas_manyandbelongs_tocanbeseenintheRailsAPI http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html#meth od-i-has_many http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html#meth od-i-belongs_to • Theyareclassmethodsfrom ActiveRecord::Associations::ClassMethods • Their method signatures are: has_many(name, scope = nil, options = {}, &extension) belongs_to(name, scope = nil, options = {}) A/Prof. Andy Song RMIT University 2021 29 Association methods has_many :friends, -> { where(author_id: 1) },
through: :societies, source: :member, do
def find_or_create_by_name(name)
first_name, last_name = name.split(” “, 2) find_or_create_by(first_name: first_name, last_name: last_name)
end end
belongs_to :firm, foreign_key: “client_of”
belongs_to :person, primary_key: “name”, foreign_key: “person_name” belongs_to :author, class_name: “Person”, foreign_key: “author_id” belongs_to :project, -> { readonly }
belongs_to :attachable, polymorphic: true
belongs_to :valid_coupon, ->(o) { where “discounts > ?”, o.payments_count },
class_name: “Coupon”, foreign_key: “coupon_id”
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Run the application
• Through these association methods Rails knows the connection between models.
• Rails does not add automatic checking or validation to ensure that the relationships would work.
• E.g.doesnotrequireavalidstudentIDforeveryaward.
• Although that can achieved using scope, option
• Now you can start the Students Application $ rails db:migrate
$ rails s
• Create new students at localhost:3000/students/new
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Adding new records
How about create an award at
localhost:3000/awards/new
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Add an Award
• Aselectfieldsoundslikeagoodideatosolvetheproblem.
• Editthestudentfieldinpartialapp/views/awards/_form.html.erb
• Remove <%= form.number_field :student_id, id: :award_student_id %> and change to
< div class =" field" >
<%= form.label :student_id %>
<%= form.select :student_id, Student.all.order(:family_name, :given_name).collect {|s| [( s.given_name + " " + s.family_name), s.id]}%>