rails migration 增長索引

uniq:惟一索引

給已有字段添加 rails generate migration add_index_to_table_name column_name:uniq

or

新增字段時增長索引 rails generate migration add_column_name_to_table_name column_name:string:uniq:index

生成

class AddIndexToModerators < ActiveRecord::Migration
  def change
    add_column :moderators, :username, :string
    add_index :moderators, :username, unique: true
  end
end