Database Migration

Show all tables in database via concole

ActiveRecord::Base.connection.tables

Reset Database

rails db:reset

model without timestamp

rails g model product --no-timestamps rails g model style --no-timestamps

Add index to column

rails g migration AddRefNumToProducts ref_num:string:index

rails g migration add_style_to_product style:references

Add references to column

rails g migration AddStyleToProducts style:references

Raise activemethod irreversible migration

(Type of exception: in the model down method) raise ActiveRecord::IrreversibleMigration

Undo last Migration

rails db:rollback

Migrate status

rails db:migrate:status

Revert Migration

rails g migration revert_add_style_to_products

require_relative '20200612070523_add_style_to_product'
class RevertAddStyleToProducts < ActiveRecord::Migration[6.0]
  def change
    revert AddStyleToProduct
  end
end

Join Table

(mailing_lists and products)

rails g migration create_join_table_products_mailing_lists mailing_lists products

Control Migration Output

puts "Message" say "Message", indent:true

say_with_time 'Message' do sleep 5 end

supress_messages do puts 'Hello from puts' say "hello from say" say "hello from say", true end

rails db:migrate VERBOSE=false

Dump the database schema

rails db:schema:dump rails db:schema:load

rails db:structure:dump rails db:structure:load

Define seed data

Character.create(name: 'Luke', movie: movies.first)

CRUD Record with a block

Create Record with a block

product = Product.create do |p| p.name = 'Fancy Couch' p.price = 65.34 end product.save

Update Record with a block

product.update_attribute(:name, 'xyz') product.update_attribute(:name => 'xyz') product.update(:name => 'xyz')

@products.each do |product| product.update_attribute(:visible => true) end

Class Method Product.update_all(:visible => true)

Delete Record with a block

product.destroy product.delete

@product.each do |product| product.destroy end

Class method

Product.destroy(152) Product.destroy([152,153,158])

product.outdated.destroy_all product.outdated.delete_all

*** Touch Record ***

product.touch # updates updated_at product.touch(:restocked_at) updates restocked_at product.touch(:restocked_at, :time => 2.minutes.ago)

Toggle attribute value

blog_post = BlogPost.find(123) blog_post.published? //false

blog_post.toggle(:published) blog_post.published? //true

hint! not changed in database

if you also need to change in database as well you can do it with the bang(!)

blog_post.toggle!(:published)

Increment and Dec columns values

product.increment(:qty_sold) # increment by 1 product.increment(:qty_sold, 5) # increment by 5

// fresh copy from database product.reload

to make changes in database product.increment!(:qty_sold, 5) # increment by 5

Track changes to Object

product.changed? # true product.changed # ["name"]

product.changes # {"name" => ["BlueSHirt", "GreenShirt"]} product.changed_attribute # {"name" => ["BlueSHirt"]} // only original values

product.save

*** trach changes to attribute *** product.name_changed? product.name_change product.name_was

product.name_changed(:from => "Couch", :to => "Sofa") # true

*** Restore Attributes *** product.restore_attributes //similar to : product.name = product.name_was

Other find Recored

find_by // return single object insted of array of object like in where clause find_by_attr

Product.find_by(:name => 'couch')

*** Dynamic Finder *** Product.find_by_name('Couch') #first match Product.find_by_name_and_price('Couch', 500) #first match

*** Assign if not find *** Product.find_or_create_by(:name => 'couch')

exists?

any?

many?

Product.where(:name => 'couch') # array Product.exists?(:name => 'couch') #boolean

Product.where(:name => 'couch').any? # boolean Product.where(:name => 'couch').many? # boolean

Select Partial Record Data (Remaining)

Join Tables Query

products = Product.joins(:category).all *** One Query instead of two queries *** products = Product.joins(:category).where(:categories => {:name => 'Furniture'}) products = Product.joins(:category).where(:categories => {:name => 'Furniture'}).count products = Product.joins(:category).order('categories.name ASC').all

*** Two Queries *** category = Category.find_by_name("Furniture") products = Product.where(:categery_id => category.id)

Distinct Record

Product.joins(:category).pluck(:name) Category.joins(:product).distinct.pluck(:name) *** Left Outer Joins *** Category.lef_outer_joins(:product).distinct.pluck(:name)

Eager Loading

products.each do |product|
  names << product.category.name 
end

vs

products.includes(:category).all

products = Product.includes(:category).where("categer.name = 'Furniture').references(:category)

products = Product.includes(:category).where(:category => {:name => "Furniture"})

Associations