Migration Details

Posted by On 2月 09, 2014 0 Comment

To change schema, we use migration file(system).

How to make migration file

  1. rails generate model with Model
  2. rails generate migration with Migration file

How to make migration file by name

We can use following

** Recommendation **
Add operation name to migration file name
AddXxxxToTableName, RemoveXxxxFromTableName etc…
example

rails generate migration AddPriceToItems price:integer

How to implement migration file



class CreateItems < ActiveRecord::Migration
  def change
    create_table :items do |t|
      t.integer :user_id
      t.string :title
      t.string :memo
      t.datetime :created
      t.timestamps
    end
  end
end
[/bash]
We add type definition into change method.

Use class which extends ActiveRecord::Migration

For other objectives, we use up, change, down methods.

Separate operations or get all together in change.


Separate


class AddTitleToItems < ActiveRecord::Migration
   def up
      add_column :items, :title, :string
   end
   def down
      remove_column :items, :title
   end
end
&#91;/ruby&#93;

<h4>change method</h4>
[ruby]
class AddTitleToItems < ActiveRecord::Migration
   def change
      add_column :items, :title, :string
   end
end
&#91;/ruby&#93;

<h3>Create table options</h3>
create_table
[ruby]
create_table :items[,toptions] do |t|
   t.type fname
end



You can add table options





Option
Description
Default Value




:id
Whether id is generated as primary key
true




:primary_key
Primary key name(if :id is true)
id




:temprary
Create temporary table name
false




:force
When creating table, drop old table or not
false




:options
Others
–





What is :option?

Example) Mysql InnoDB


:options => 'ENGINE=InnoDB CHARSET=utf-8'



Options Example


create_table(:objects, primary_key: 'guid') do |t|
  t.column :name, :string, limit: 80
end



Field Definition


Example: t.datatype :columnname

Field definition should be under create_table.





Migration
SQLite
Ruby




integer
INTEGER
Fixnum




decimal
DECIMAL
BigDecimal




float
FLOAT
Float




string
VARCHAR(255)
String




text
TEXT
String




binary
BLOB
String




date
DATE
Date




datetime
DATETIME
Time




timestamp
DATETIME
Time




time
TIME
Time




boolean
BOOLEAN
TrueClass/FalseClass





Migration type is type you use in create_table method.

SQLite is SQLite prepared data type, Ruby is ruby class


Wow, Blob is String in Ruby?


Column Flag


t.datatype :columnname, :flagname => value





Flag
Description




:limit
Limitation number




:default
Default value




:null
null is allowed?




:precision
Total digit




:scale
digit under a decimal point





Example


t.string :name, :limit => 17, :null => false
t.string :title :limit => 100, :null => false
t.decimal :price, :precision => 5, :scale => 0
t.string publish, :limit => 20, :default => 'ABC出版'



Migration Methods


You can use following methods





Name
Description




add_column
Add new column




add_index
Add new index




add_timestamps
Add created_at, updated_at




change_column
Change definition of column




change_column_default
Change default value




change_table
Change table definition




column_exists?
Check column is existed or not




create_table
Create new table




drop_table
Delete table




index_exists?
Check index is existed or not




remove_column
Delete column




remove_index
Delete index




remove_timestamps
Delete existed created_at, update_at, there are added by default




rename_column
Change column name




rename_index
Change index name




rename_table
Change table name




execute
Execute SQL directly





Change table definition


Use change_table

Table layout, index add/delete etc…


Example


change_table :books do |t~
   t.string :author # Add author column(string)
   t.remove :publish, :cd   # Delete publish, cd column
   t.index :title   # Add index to title
   t.rename :isbn, :isbn_code   # Change column name from isbn to isbn_code
end



Methods


There are methods we can use in change_table


    

  • index
    • 

  • change
    • 

  • change_default
    • 

  • rename
    • 

  • remove
    • 

  • remove_references
    • 

  • remove_index
    • 

  • remove_timestamps
    • 



Index(add_index, remove_index)


Options





Option
Description




:unique
Add unique constraint or not




:name
Index name




:length
Length included index(not for SQLite)





Example


add_index :books, title
add_index :books, [:publish, :title]    # multi column index
add_index :books, [:publish, :title], :unique => true, :name => 'idx_pub_title'
remove_index :books
remove_index :[:publish, :title]



SQL(execute)


Execute SQL directly.


Situation


    

  • Add special data type
    • 

  • Foreign key constraint
    • 

  • Check constraint
    • 

  • Other database special setting
    • 



Example


execute "CREATE VIEW view_books AS SELECT * FROM books WHERE title = 'ABC'"



Be careful to execute SQL because sometimes doesn’t work after changeing!

  					

 			 
	
			 
					   					

										

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