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Migrations and Misc Rails Reference Cheat Sheet (DRAFT) by

This is a draft cheat sheet. It is a work in progress and is not finished yet.

ORM (Object Relational Mapping)

Advantages
DB indepe­ndent. moving from PG to Sqlite should be trivial.
Cleaner code focused on business logic rather than SQL Query
Relati­ons­hip­/As­soc­iation Management
Model Objects can be cached -- No need to repeatedly query DB for same data
Transa­ction support
Built in validation before save
Disadv­antages
Abstra­ction = overhead (uses more memory etc...)
SQL ignorance

Create Table (with Datatypes)

# CREATE

class CreateOrders < ActiveRecord::Migration[5.1]
  def change
    create_table :orders do |t|
      
       t.belongs_to :category

       t.binary :photo # PG: bytea   MySQL: blob
       t.boolean :success # PG: boolean   MySQL: tinyint(1)
       t.date :ship_date # PG & MySQL: date  
       t.datetime :order_date # PG: timestamp   MySQL: datetime
       # PG & MySQL: decimal  Precise.  Use for currency, geolocation
       t.decimal :latitude, :decimal, :precision => 15, :scale => 13 
       t.float  # PG & MySQL: float  Less precise thank decimal
       t.integer :age # PG: integer   MySQL: int(11)
       t.string :name # PG & MySQL: varchar(255)  
       t.text :comments # PG & MySQL: text  
       t.time :ship_time # PG & MySQL: time  
       t.timestamps  # PG: timestamp   MySQL: datetime

    end
  end
end
 

Generators

rails g model comment post:r­efe­rences text:s­tring
rails g migration add_po­st_­to_user post:b­elo­ngs_to
rails g migration AddUse­rRe­fTo­Pro­ducts user:r­efe­rences
rails g migration AddPar­tNu­mbe­rTo­Pro­ducts part_n­umb­er:­string
rails generate controller Sessions new

rails db: command

Rollback the last migration:
rails db:rol­lback
Revert the last 3 migrat­ions:
rails db:rol­lback STEP=3
Rollback and then migrating back up:
rails db:mig­rat­e:redo STEP=3
Run specific migration
rails db:mig­rate:up VERSIO­N=2­008­090­6120000
Load test fixtures
rails db:fix­tur­es:load
Create a db/sch­ema.rb file that can be portably used against any database supported by Active­Record
db:sch­ema­:dump
Load a schema.rb file into the database
db:sch­ema­:load
Dump database structure to SQL file Drops the database, creates the datab
db:str­uct­ure­:dump
Clone your database structure into the test database
db:tes­t:p­repare
Drops the database, creates the database and then runs migra- tions against the database. Takes a VERSION argument as well as RAILS_ENV
db:reset
Create­/clear Sessions table
db:ses­sio­ns:­create (or :clear)

Postgres Specific Data Types

:hstore	# Key => Val Hash Store
:json	        #The json data type stores an exact copy of the input text
:jsonb	# stored in a decomposed binary format
:array	
:cidr_address	#IP Address
:ip_address	#IP Address
:mac_address	#String
In other DBs these are all stored as strings

Change Table

class AddPartNumberToProducts < ActiveRecord::Migration[5.0]
  def change
    
    add_index :products, :part_number
    remove_index :products, :part_number

    add_reference :this_table, :other_table, index: true
    remove_reference :this_table, :other_table, index: true
    
    belongs_to: 
    add_column :products, :part_number, :string
    add_column :products, :column_name, :string, :limit => 50    

    rename_column :shoes, :season, :season_id
    t.change :column_name, :new_column_type
    change_column_default :table_name, :status, 0
    t.remove :column_name
    

  end
end