Ruby on Rails : Still Relevant ?

Rails 5 Tour

Useful Rails 5 Expressions

Select All Fields (columns)  in a Table

def index
   @orders = Order.all
end

Select Some Fields (columns)  in a Table

def index
   @orders = Order.select(:product, :price, :quantity)
end

More at http://blog.bigbinary.com/2016/05/24/rails-5-adds-active-record-ignored-columns.html

Display All Rows  in a Table

def list
   @orders = Order.all
end

The @orders = Order.all line in the list method tells Rails to search the orders table
and store each row it finds in the @orders instance object.

Display Target Row  in a Table
 
def show
   @orders = Order.find(params[:id])
end

The @orders = Order.find(param[:id]) line in the show method tells Rails to search 
the orders table and store the target row it finds in the @orders instance object.

What happens when you generate a scaffold in Rails 5 ?

Q. What happens when you rails g scaffold Employee eno:string ename:string dept:string date_join:date active:boolean ?

ANSWER

1. Migration file created as yyyymmddhhmmss_create_employees.rb

CreateEmployees < ActiveRecord::Migration[ 5.0]

  def change    
    create_table :employees do |t|
      t.string :eno      
      t.string :ename      
      t.string :dept      
      t.date :date_join      
      t.boolean :active
      t.timestamps
    end  
  end
end

2. Employee Model created as employee.rb

class Employee < ApplicationRecord
end

3. Employees Controller created as employees_controller.rb

class EmployeesController < ApplicationController  
  before_action :set_employee, only: [:show, :edit, :update, :destroy]

  # GET /employees  # GET /employees.json  
  def index    
   @employees = Employee.all
  end

  # GET /employees/1  # GET /employees/1.json  
  def show  
  end
 
  # GET /employees/new    
  def new    
     @employee = Employee.new
  end

  # GET /employees/1/edit  
  def edit  
  end
  
  # POST /employees  # POST /employees.json  
  def create    
   @employee = Employee.new(employee_params)
    respond_to do |format|
      if @employee.save
        format.html { redirect_to @employee, notice: 'Employee was successfully created.' }
        format.json { render :show, status: :created, location: @employee }
      else        
        format.html { render :new }
        format.json { render json: @employee.errors, status: :unprocessable_entity }
      end    end  end

  # PATCH/PUT /employees/1  # PATCH/PUT /employees/1.json  
   def update    
      respond_to do |format|
      if @employee.update(employee_params)
        format.html { redirect_to @employee, notice: 'Employee was successfully updated.' }
        format.json { render :show, status: :ok, location: @employee }
      else        
        format.html { render :edit }
        format.json { render json: @employee.errors, status: :unprocessable_entity }
      end    end  end
  
 # DELETE /employees/1  # DELETE /employees/1.json  
   def destroy    @employee.destroy
    respond_to do |format|
      format.html { redirect_to employees_url, notice: 'Employee was successfully destroyed.' }
      format.json { head :no_content }
    end  
  end
  
 private    
   # Use callbacks to share common setup or constraints between actions.    
   def set_employee      
     @employee = Employee.find(params[:id])
    end
   
   # Never trust parameters from the scary internet, only allow the white list through.    
   def employee_params      
     params.require(:employee).permit(:eno, :ename, :dept, :date_join, :active)
   end
  end


4. Views created under Views/employees folder

_form.html.erb, edit.html.erb, new.html.erb and show.html.erb automatically created










5. Tests folder

Test files for controllers employees_controller_tests.rb
Test files for models employees_tests.rb
Test files for fixtures employees.yml




6. Routes: resources:employees

Ruby Language : Must Know Basic

Quotation Marks

'' = no evaluation
"" = evaluation done

Given a Model, how to loop through all properties?

Q. I want to loop through all the properties of my 'user' model, how can I do this ?

A. If you have an instance of your model then user.attributes is a Hash of the model's attributes and their values so, for example, you can do something like:

user.attributes.each_pair do |name, value|
  puts "#{name} = #{value}"
end

If you don't have a specific instance then the class has methods that return information about the fields in the database e.g. User.columns and User.content_columns. e.g.

User.columns.each do |column|
  puts column.name
end

How to loop through every record in a Database Table ?

Here is the correct syntax to iterate over all User Table :
Also, to improve performance, you may want to use User.find_each
(see doc) instead of User.all

User.all.each do |user|
  #the code here is called once for each user
  # user is accessible by 'user' variable
end

User.find_each do |user|
  #the code here is called once for each user
  # user is accessible by 'user' variable
end