ROR Database and MIgration .

[Migration, Database Setting, DB Import/Export, Association, Model]

[SQL]

DB DUMP :- (Import/Expert)

Export one DB

$> mysql -u root -p database_name > dump_file {syntax}

$> mysqldump -u root -p gps_whatif > gps_whatif_db.sql

$> Password

Export one table

$> mysql -u root -p database_name table_name > dump_file {syntax}

$> mysqldump -u root -p gps_whatif products > gps_pro.sql

$> Password

Import products table into DB

$> mysql -u root -p database_name < dump_file {syntax}

$> mysql -u root -p gps_whatif < gps_pro.sql

$> Password

ROR Migration :-

What is Migration & Its Advantage ?

Migrations are a convenient way for you to alter your database in a structured and organized manner.

Rails Migration allows you to use Ruby to define changes to your database schema.

Making it possible to use a version control system to keep things synchronized with the actual code.

Adv:-

Teams of developers : If one person makes a schema change, the other developers just need to update, and run "rake migrate".

Production servers : Run "rake migrate" when you roll out a new release to bring the database up to date as well.

Multiple machines: If you develop on both a desktop and a laptop, or in more than one location, migrations can help you keep them all synchronized.

List out what can Rails Migration do?

• Create table
• Drop table
• Rename table
• Add column
• Rename column
• Change column
• Remove column and so on

What are the different process and syntax of migration ?

$> rails g migration filename {syntax}

$> rails g migration addNameToUser

$> rails g migration addNameToUser name:string

N:- only migration file will generate

$> rails g model modelname {syntax}

$> rails g model user name:string age:string

N:- modelname must be singular, by this command we will get both model & migration file generated. After that we can change migration file asper need create table, add column, rename etc

[Migration file change]

1/Creating table name

class CreateUsers < ActiveRecord::Migration

def change

create_table :users do |t|

t.string :firstname

t.timestamps null: true

end

end

end

2/ Add a Column to Table

class AddColumnToOrganisation < ActiveRecord::Migration

def change

add_column :table_name, :column_name, :data_type

end

end

3/ Rename column name of a Table

rename_column :table_name, :old_name, :new_name

4/ Change data type of a column

change_column :table_name, :column_name, :new_datatype

5/ Drop a column of a table

remove_column :table_name, :column_name

6/ Drop a table

drop_table :table_name

7/ add new features to column like Uniqueness

add_index :users, :fname, unique: true

Database Setting :-

project/config/database.yml

default: &default

adapter: mysql2

pool: 5

timeout: 5000

development:

<<: *default

database: sample_test

username: root

password: orbio123

production:

<<: *default

database: sample_test

username: root

password: orbio123

N:- In database.yml we need to mension adapter: mysql2 either in default: or development:

and we need to add gem in Gemfile ---- gem 'mysql2'

and bundle install

Multiple database in single application

project/config/database.yml

default: &default

adapter: mysql2

pool: 5

timeout: 5000

development:

<<: *default

database: sample_test

username: root

password: orbio123

development_sec:

adapter: mysql2

database: sample

username: root

password: orbio123

host: localhost

production_sec:

<<: *default

database: sample

username: root

password: orbio123

N :- development: is default env so we do not need any connection explicitly .

But for production_sec: env we need to connection explicitly as below

project/app/model/group.rb (groups table in sample_test database)

class Group < ActiveRecord::Base

establish_connection "#{Rails.env}_sec"

end

[Migration for Second Database]

$> rails g migration subgroup

project/db/migrate/migrationfile.rb

class CreateConections < ActiveRecord::Migration

def connection

ActiveRecord::Base.establish_connection("#{Rails.env}_sec").connection

end

def change

create_table :conections do |t|

t.timestamps null: false

end

end

end

N :- connection action can not be any other action.