ruby-on-rails - Add column to table and fix value for existing records in Rails

Question

I want to add a column called "payment_type" into my "orders" table.

Here is the migration that I have so far:

def change
  add_column :orders, :payment_type, :string
end

I want that payment_type to hold the value "normal" for all the records that currently are in the DB. However, not for the future records. I want no default value for future records. How can I do this?

Answer 1

由于您只想为所有现有记录设置值，因此可以使用update_all，这比遍历所有订单实例要快得多，因为它仅使用数据库语句并且不实例化所有订单：

class Order < ActiveRecord::Base
end

def up
  add_column :orders, :payment_type, :string
  Order.reset_column_information
  Order.update_all(payment_type: 'normal')
end

def down
  remove_column :orders, :payment_type
end

update_all不调用任何验证或触发器。

Answer 2

我认为最简单的方法是：

  class AddStateToSites < ActiveRecord::Migration[5.1]
      def up
        add_column :sites, :state, :string, default: :complete # sets default value for existed records
        change_column :sites, :state, :string, default: nil # changes default value for next
      end

      def down
        remove_column :sites, :state
      end
    end

然后在控制台中检查它：

>> Site.last.state
  Site Load (0.6ms)  SELECT  "sites".* FROM "sites" ORDER BY "sites"."id" DESC LIMIT $1  [["LIMIT", 1]]
=> "complete"
>> Site.new.state
=> nil

Answer 3

def change
  add_column :orders, :payment_type, :string
  Order.all.each do |order|
    order.update_attributes(:payment_type => 'normal')
  end
end

Answer 4

正如其他人所提到的，依赖将来可能会被删除的类并不是一个好习惯，因为它会在那个时候阻止迁移。

相反，我使用直接执行原始 mySQL：

execute "UPDATE `orders` SET `payment_type` = 'normal'"

Answer 5

如果您想通过迁移更新列棒，那么上面的答案很棒， 但是如果您想在自己的机器上本地更新列，以便在共享代码时其他人无法看到更新的属性，只需转到 Rails 控制台并循环...

orders = Order.all

 orders.each do |o|
   o.update_attribute(:payment_type, 'normal')
 end

导轨 4