enum field 怎样保存nil 值

我只是想在 enum 字段保存一个 nil 值, 居然报错 enum is not valid industry

Env:

Rails version = 4.0.13

migration

  create_table :model_table do |t|
     t.industry :integer
  end

model

  class ModelName < ActiveRecord::Base
    INDUSTRY = {"online_travel" => 100 ,"entertainment" => 110 ,"other" => 120}
    enum industry: INDUSTRY
  end

执行的 action

　def create
    model = ModelName.new
    model.industry = nil
  end

居然报错 enum is not valid industry

查了文档 enum 方法, 居然没有 allow_blank: true 之类的设置.

官方给的best practice 是加一个 default: 0, here. 可是之前同事发布时, mysql执行default时间太长的引发了故障，不敢用这个。

意淫了一把，把 model 弄成这样：

solution:

model

  class ModelName < ActiveRecord::Base
    INDUSTRY = {"online_travel" => 100 ,"entertainment" => 110 ,"other" => 120,  '' => nil}
    enum industry: INDUSTRY
  end

设置 model.industry = nil，竟然可以!!

action

  model = ModelName.new
  model.industry = ''   # good
  model.industry = nil  # good