Rails Active Record在before_create回调中取消（保存或创建）而不引发异常

Question

Actually, I want to test a model callback.

system_details.rb (Model)

class SystemDetail < ActiveRecord::Base
  belongs_to :user
  attr_accessible :user_agent

  before_create :prevent_if_same    

  def agent
    Browser.new(ua: user_agent, accept_language: 'en-us')
  end

  def prevent_if_same
    rec = user.system_details.order('updated_at desc').first
    return true unless rec
    if rec.user_agent == user_agent
      rec.touch
      return false
    end
  end
end

prevent_if_same method is working fine and working as expected but it raises exception ActiveRecord::RecordNotSaved when it returns false, and the exception breaks the rspec test .what I want is, It should silently cancel save without raising an exception.

system_detail_spec.rb (rspec)

require 'rails_helper'

RSpec.describe SystemDetail, :type => :model do      

  context '#agent' do
    it 'Checks browser instance' do
      expect(SystemDetail.new.agent).to be_an_instance_of(Browser)
    end
  end

  context '#callback' do    
    it 'Ensure not creating consecutive duplicate records' do
      user = create :end_user
      system_detail = create :system_detail, :similar_agent, user_id: user.id
      updated_at  = system_detail.updated_at
      system_detail2 = create :system_detail, :similar_agent, user_id: user.id
      system_detail.reload

      expect(system_detail2.id).to be_nil
      expect(system_detail.updated_at).to be > updated_at
    end
  end        
end

The 2nd test #callback was failing because of exception.

Failures:

1) SystemDetail#callback ensure not creating duplicate records Failure/Error: system_detail2 = create :system_detail, :similar_agent, user_id: user.id ActiveRecord::RecordNotSaved: ActiveRecord::RecordNotSaved

Is there any way to silently cancel save without raising an exception?

Answer 1

I think in this case is better to use validate :prevent_if_same because basically your method is kind of validation rule. Also it would prevent from creation silently. You can always add error if you want to notify user about unsuccessful creation