rails check_used for destroy

check_used.rb

# customer.rb

before_destroy :check_used

def allow_destroy?
  @allow_destory ||= LoadingBill.exists?(:author_id => self.id)
end

protected
  def check_used
    unless self.allow_destroy?
      self.errors.add_to_base("此客户已经有提单了, 不能删除")
      raise ActiveRecord::RecordInvalid.new(self)
    end
  end
  
# test_customer.rb

test "destroy a customer that has loading_bills" do
  assert_raise(ActiveRecord::RecordInvalid) do
    customers(:ibm).destroy
  end
  assert_match(/已经有提单/, customers(:ibm).errors.full_messages.to_s)
end
  
# test_customers_controller.rb  

test "destroy success" do
  customer = Customer.last
  customer.loading_bills.delete_all
  delete :destroy, :id => customer
  assert_redirected_to customers_url
  assert !Customer.exists?(customer.id)
end

test "destroy invalid" do
  customer = Customer.last
  assert_raise(ActiveRecord::RecordInvalid) do
    delete :destroy, :id => customer
  end
end

# 最在 index.html.erb 

<%= link_to_if user.allow_destroy?, "删除", user, :confirm => "你确定删除吗?", :method => :delete %>