Active Record in Railsby Farhan Faruque

Topics

❏ Basics❏ Active Record Migrations❏ Active Record Validations

Active Record- What?

❏ an ORM (Object Relational Mapping).❏ a layer of Ruby code that runs between your

database and your logic code.

Convention over Configuration● if you configure your applications in the very same way most of the time

then this should be the default way● Database Table - Plural with underscores separating words (e.g.,

book_clubs).● Model Class - Singular with the first letter of each word capitalized (e.g.,

BookClub).

Model/class Table / Schema

BookClub book_clubs

Post Posts

Creating Active Record ModelsModel

class Post < ActiveRecord::Base attr_accessor :title,:descend

Database

CREATE TABLE Posts ( id int(11) NOT NULL auto_increment, title varchar(255), desc text, PRIMARY KEY (id));

CRUD: Reading and Writing Data

Create

post = Post.create(title: ‘Cricket WC’,desc:’2015 Australia’) Read

post = Post.all # return a collection with all users

post = Post.where(title:’Cricket WC’)Update

post = Post.find_by(title:’Cricket WC’)post.desc = ‘Cricket World cup - 2015’post.save

deletepost.destroy

Migrations - Basic

❏ Alter Database and Schema in a consistent way❏ database independent❏ each migration as being a new 'version' of the database

Migration - Example$ rails generate model location name:string description:textclass CreateLocation < ActiveRecord::Migration def change create_table :location do |t| t.string :name t.text :description t.timestamps null: false end endend

Creating Migration$ rails generate migration AddStreetToLocations street:stringclass AddStreetToLocation< ActiveRecord::Migration def change add_column :locations, :street, :string endend

● stored as files in the db/migrate directory● The name of the file is of the form YYYYMMDDHHMMSS_add_street_to_location.rb

Migration - convention

Convention Example Generates in Change

AddXXXToXXX AddStreetToLocation street:string add_column :locations, :street, :string

RemoveXXXFromXXX RemoveStreetFromLocation street:string

remove_column :location, street :string

CreateXXX CreateLocation create_table :location

XXXRefToXXX AddCountryRefToLocation add_reference :Location, :country, index: true

XXXJoinTableXXX CreateJoinTableCustomerProduct customer product

create_join_table :customers, :products

Changing table and column

change_column :location, :latitude, :string

change_table :products do |t| t.remove :description, :nameend

Migration - Passing Modifiers$ bin/rails generate migration AddDetailsToProducts 'price:decimal{5,2}'class AddDetailsToProducts < ActiveRecord::Migrationdef change add_column :products, :price, :decimal, precision: 5, scale: 2 endendModifiers Type● limit● required● default● etc..

Using the up/down Methods❏ same as change method❏ used before rails-3.1❏ up method use for transformation❏ down method for revert up

Running Migration❏ $ rake db:migrate

- run current migration❏ $ rake db:migrate VERSION=20080906120000

- run specific version❏ $ rake db:rollback

- roll back to previous version❏ $rake db:migrate RAILS_ENV=test

- run migration in test environement

Active Record Validations - Why?

❏ ensures valid data❏ model-level validation

Others ways of validations problems

❏ Database Constraints- database dependent

❏ Client-side validations- unreliable

❏ Controller-level validations- difficult to test and maintain

Example

class Location < ActiveRecord::Base validates :name, presence: trueend

Person.create(name: "John Doe").valid? # => truePerson.create(name: nil).valid? # => false

Validation triggers❏ create❏ create!❏ save❏ save!❏ update❏ update!

Validations Helpers❏ acceptanceclass Person < ActiveRecord::Base validates :terms_of_service, acceptance: trueend

❏ confirmationclass Person < ActiveRecord::Base validates :email, confirmation: trueend

Other Validations Helpers❏ length❏ numericality❏ validates_associated❏ exclusion❏ format❏ presence❏ uniqueness❏ etc..

Common options

:allow_nil:allow_blank:message:on

Conditional Validation

:if and :unless❏ a symbol :a method name❏ a string :a really short

condition❏ a proc :an inline condition

Example - with a methodclass Order < ActiveRecord::Base validates :card_number, presence: true, if: :paid_with_card?

def paid_with_card? payment_type == "card" endend

Custom Validations❏ Inherited from Two moudles

➢ ActiveModel::Validator➢ ActiveModel::EachValidator➢ get the ‘record’ argument as parameter

❏ Custom method and helpers

Working with Validation Errors

❏ errors.messages❏ errors[:attr] # for a specific attribute❏ errors.add(:attr,message) ❏ errors[:base] #object’s state as a whole❏ errors.clear #clear errors❏ errors.size #count of errors

Displaying Validation in Views