• The Problems of database migration.
• How ruby on rails handle the table changes
• How our team to handle the database changes

databasemigration1.png

Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.

Agile requires us to embrace changes, but:

1. It is difficult to get the change sets of the release.
2. It is difficult to get the dependence between web and ods.
3. If we need reload a table or UDF, we must drop the related UDF first.
4. We can not roll back table or stored procedure easily.
5. It is difficult to prepare replication change request.
6. It is difficult to identify which stored procedure will be impacted by a specific CR.

The design of Rails was driven by a couple of key concepts: DRY and convention over configuration.

Rails uses the power of Ruby to bring that to life. You'll find very little duplication in a Rails application; you say what you need to say in one place-a place often suggested by the conventions of the MVC architecture-and then move on. For programmers used to other web frameworks, where a simple change to the schema could involve them in half-a-dozen or more code changes, this was a revelation.

ActiveRecordMigration 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.

This has many uses, including:

• Teams of developers - if one person makes a schema change, the other developers just need to update, and run "rake db:migrate".
• Production servers - run "rake db: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.

Run the generator:

ruby script/generate migration add_a_new_table

This will create the file db/migrate/001_add_a_new_table.rb

The method self.up is used when migrating to a new version, self.down is used to roll back any changes if needed.

 class AddANewTable < ActiveRecord::Migration
   def self.up
     create_table :users do |table|
       table.column :name, :string
       table.column :password, :string, :limit => 32, :null => false
      end
   end
   def self.down
     drop_table :users
   end
end

There is a table in database to track the version.

<#+BEGIN_SRC > rake db:migrate #+END_SRC

<#+BEGIN_SRC > rake db:migrate VERSION=17 #+END_SRC

1. Change Set

Copy the changed files since the last release.

1. Dependence and impacted store procedure

Using shell script to query the catalog table to get the relationship of the DB object.

1. Rollback and table changes

It is not very necessary to support rollback. Use alter to change the table.