In Ruby on Rails 3.2.3, I changed the default value of a database column, so here’s a memo.

change_column_default(table_name, column_name, default)
Sets a new default value for a column.
Examples
change_column_default(:suppliers, :qualification, ‘new’)
change_column_default(:accounts, :authorized, 1)
change_column_default(:users, :email, nil)

・Source: ActiveRecord::ConnectionAdapters::SchemaStatements

For example, if you want to change the articles table’s title column definition from “String type, NOT NULL constraint: yes, default value: empty string” to “String type, NOT NULL constraint: no, default value: NULL”, the migration file would be written as follows:

class ChangeTitleNullToArticles < ActiveRecord::Migration
  def up
    change_column :articles, :title, :string, null: true
    change_column_default :articles, :title, nil
  end

  def down
    change_column :articles, :title, :string, null: false
    change_column_default :articles, :title, ""
  end
end

That’s all from the Gemba.