Ruby on railscourse

Day 3

M for Model

Agenda

ActiveRecord Basics

Associations

Validations

Callbacks

Query Interface

Active record and MVC

What’s ActiveRecord ?

What to expect from ActiveRecord Model.

associations.

inheritance.

validations.

OO DB operations.

Convention over configuration.

Active RecordAn object that wraps a row in a database table, encapsulates the database access and adds domain

logic on that data.

What to expect from ActiveRecord Model?

associations.

Relations to different models to simulate one2many, many2one self joins, etc..

inheritance.

also is considered as relation however it’s parent-child relationship between models.

validations.

validation logic

OO DB operations.

Business logic example:

ahmed = User.last ahmed.joined_course(“math”)

Convention over configuration

Model class name and table name

Foreign and primary key convention:

FK: <table_name>_id

PM: id

Rails g model <model_name> [field:type, ]

Creates model file

Creates model test

Created migration file.

Associations

belongs_to

has_one

how is that different than belongs_to ?

through

has_many

through

has_and_belongs_to_many

belongs_to

One2One connection.

single model

belongs_to :department

has_one

has_one is One2One connection.

single model

has_one <model>

No FK required in model, it’s pointed in the other model.

through is the intermediate junk table.

has_manypointing to me.

has_many through :modelVS. has_and_belongs_to_many

Self Join

class_name

foreign_key

class Employee < ActiveRecord::Basehas_many :subordinates, class_name: "Employee",foreign_key: "manager_id"

Validations

Built-invalidates :name, presence: true, length: {minimum: 3}

Class Validator, EachValidator

Template design pattern

Methods

on:

Call Backs

Before, after and around ->SaveSave<- ->Save<-

When

Create, update, destroy

Save, validate

Executio

n o

rder

Destroy

Update

Create

Query interface

find(id or array(id))

take, first, last

find_by(key: value)*

where

? for sql injection

hash conditions

Ordering

Selecting

Group and Having

includes*

limit and offset

*find_each will be used with huge amount of records *includes will eager load all associated models for less queries.

Thank you!