爲什麼nil：試圖訪問model.rb中的self.attribute時發生NilClass錯誤？

Question

我想在Employee模型上寫一個date_of_birth attr我自己的驗證，我沒有看到我的錯誤，我敢肯定這是真正愚蠢的，在我的鼻子下面。代碼如下，我的錯誤信息是;

NoMethodError: 
    undefined method `<' for nil:NilClass 

employee.rb

class Employee < ApplicationRecord 
    belongs_to :quote 

    validates_presence_of :first_name, :last_name, :email, :gender, :date_of_birth, :salary 
    validates :first_name, length: { minimum: 2, message: "minimum of 2 chars" } 
    validates :last_name, length: { minimum: 2, message: "minimum of 2 chars" } 
    validates_email_format_of :email, :message => 'incorrect email format' 
    validate :older_than_16 

    enum gender: [ :m, :f ] 

    private 

    def older_than_16 
     self.date_of_birth < Time.now-16.years 
    end 

end 

schema.rb

ActiveRecord::Schema.define(version: 20170620125346) do 

    # These are extensions that must be enabled in order to support this database 
    enable_extension "plpgsql" 

    create_table "employees", force: :cascade do |t| 
    t.string "first_name" 
    t.string "last_name" 
    t.string "email" 
    t.string "initial" 
    t.integer "gender" 
    t.date  "date_of_birth" 
    t.integer "salary" 
    t.integer "quote_id" 
    t.datetime "created_at", null: false 
    t.datetime "updated_at", null: false 
    t.index ["quote_id"], name: "index_employees_on_quote_id", using: :btree 
    end 

employee_spec.rb

RSpec.describe Employee, type: :model do 
    describe 'validations' do 

     it { should validate_presence_of(:date_of_birth) } 
     it { should_not allow_value(Date.today-15.years).for(:date_of_birth) } 
     # it { should allow_value(Date.today-17.years).for(:date_of_birth) } 
    end 
end 

Answer 1

您的自定義方法匹配甚至第一次測試，但self.date_of_birth叫實際上是nil所以你看到這個錯誤。
在比較之前，您必須檢查date_of_birth是否不是nil。
如果您認爲模型無效，您還必須將add a new entry設置爲errors集合。
（還要檢查你的情況，我用>，而不是<，讓您的測試通過）

def older_than_16 
     return if self.date_of_birth.nil? 
     if self.date_of_birth > Time.now-16.years 
      errors.add(:date_of_birth, "Should be at least 16 years old") 
     end 
    end