PG :: InvalidDatetimeFormat：錯誤：類型日期無效的輸入語法：「」

Question

數據庫PostgreSQL的

我有以下遷移：

class AlterBirthdayInUsers < ActiveRecord::Migration[5.0] 
    def change 
    change_column :users, :birthday, 'date USING CAST(birthday AS date)', default: Date.today 
    end 
end 

遷移已啓動的錯誤：

rake stdout: == 20170201162913 AlterBirthdayInUsers: migrating ======================= 
-- change_column(:users, :birthday, "date USING CAST(birthday AS date)", {:default=>Sat, 18 Feb 2017}) 
rake stderr: rake aborted! 
StandardError: An error has occurred, this and all later migrations canceled: 

PG::InvalidDatetimeFormat: ERROR: invalid input syntax for type date: "" 
: ALTER TABLE "users" ALTER COLUMN "birthday" TYPE date USING CAST(birthday AS date) 

date類型的遷移字段中的postgrees的正確點是什麼？

在此先感謝您的答覆。

Answer 1

但是卻沒有嘗試空字符串轉換爲日期， 變化

USING CAST(birthday AS date) 

到

USING CAST(case when birthday = '' then null else birthday end AS date)