# [rails4][migration][note]migration筆記 ###### tags: `Rails4`,`migration`,`note` ### 修改column預設值 https://stackoverflow.com/questions/8638079/how-to-set-default-value-to-column-in-rails-while-creating-migration ```c! $ rails g migration change_column1_in_table_name_plural ``` migration file ```ruby #... change_column :table_name_plural, :column_name, :integer, :default => 0 #... ``` ### 修改column type https://tosbourn.com/rails-migrate-change-column-type/ ```c! $ rails g migration change_column1_to_be_type_in_table_name_plural ``` ```ruby= class ChangePhoneToBeStringInCustomers < ActiveRecord::Migration def up change_column :customers, :phone, :string end def down change_column :customers, :phone, :integer end end ``` ### 新增unique column或將column設為unique https://stackoverflow.com/questions/1449459/how-do-i-make-a-column-unique-and-index-it-in-a-ruby-on-rails-migration >語法: >rails generate migration add_index_to_table_name column_name:uniq > ex:將username設定為unique ```terminal $ rails generate migration add_index_to_users username:uniq ``` 產生migration後先**不要**執行migrate, 開啟產生的新migration檔： ```ruby class AddIndexToUsers < ActiveRecord::Migration def change add_column :users, :username, :string #<--將此行註解或刪除 add_index :users, :username, unique: true end end ``` 修改後再執行migrate ```terminal $ rake db:migrate ``` >使用add_index語法產生migration檔,雖然只有add_index,migration還是會自動產生add_column,所以必須手動將該行註解或刪除 --- ### 新增欄位至資料表 方1(自動增加欄位) https://stackoverflow.com/questions/4834809/adding-a-column-to-an-existing-table-in-a-rails-migration ```c $ rails generate migration add_fieldname_to_tablename fieldname:string $ rake db:migrate ``` 方2(手動增加欄位) ```c $ rails generate migration add_column_name_in_table_name ``` migration檔範例 ```ruby class AddCatIdInProduct < ActiveRecord::Migration def change add_column :products, :cat_id, :integer add_index :products, :cat_id end end ``` >migration修改完後記得執行rake db:migtrate ### 新增帶有reference的migration https://stackoverflow.com/questions/22815009/add-a-reference-column-migration-in-rails-4 https://stackoverflow.com/questions/31843363/rails-how-to-delete-a-pending-migration/31843442 ```c! $ rails g migration addModelName1ToModelName2 ModelName1:references $ rake db:migrate ``` >上述語法會在ModelName2所對應的table新增ModelName1_id欄位 --- ### 移除尚未執行的migration ```c! $ rails d migration migration_name_without_date_and_time ``` ### 察看migration status ```c! $ rake db:migrate:status ``` ### 將已經執行過的最後一個migration倒回去 ```c! $ rake db:rollback ``` ---