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
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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
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Rollback the last migration: rails db:rollback
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Revert the last 3 migrations: rails db:rollback STEP=3
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Rollback and then migrating back up: rails db:migrate:redo STEP=3
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Run specific migration rails db:migrate:up VERSION=20080906120000
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Load test fixtures rails db:fixtures:load
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Create a db/schema.rb file that can be portably used against any database supported by ActiveRecord db:schema:dump
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Load a schema.rb file into the database db:schema:load
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Dump database structure to SQL file Drops the database, creates the datab db:structure:dump
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Clone your database structure into the test database db:test:prepare
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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
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Create/clear Sessions table db:sessions:create (or :clear)
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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
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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
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