如何验证和测试Rails 4中关联对象的串联创建？

Question

In my app, when a User is initialized, I want them to build 5 items. I've seen tests that assert there are, for example, expect(@user.items.count).to eq(5) . However, I've been trying to validate the length of items and test the validation itself, not the number of objects associated with a user. Is this even possible? If so, what's the best way of going about this?

Here is the relevant code I have so far.

class User < ActiveRecord::Base
  ITEMS_ALLOWED = 5
  has_many :items

  validates :items, length: {is: ITEMS_ALLOWED}
  after_initialize :init_items

  def init_items
    ITEMS_ALLOWED.times { items.build }
  end
...

My relevant test, using RSpec, Faker and FactoryGirl

describe User do
  before :each do
    @user = build(:user, username: "bob")
    @user.save
  end

  it "is invalid with more than 5 items" do
    user3 = build(:user)
    user3.save
    expect(user3.items.create(name: "test")).not_to be_valid
  end
end

Currently the test tries to validate the item that's created. I tried to move the validation to the Item class instead, but I'm receiving the error, undefined method items for nil on the line that tries to call user.items.count .

class Item < ActiveRecord::Base
  belongs_to :user

  validates :number_of_items, length: {is: 5}

  def number_of_items
    errors.add("User must have exactly 5 items.") unless user.items.count == 5
  end
end

================ Update: Failure Message when there are no validations in the Item class.

Failures:

  1) User initialization is invalid with more than 5 items
     Failure/Error: expect(user3.items.create(name: "test")).not_to be_valid
       expected #<Item id: 16, name: "test", user_id: 3, photo: nil, created_at: "2014-01-14 00:24:11", updated_at: "2014-01-14 00:24:11", photo_file_name: nil, photo_content_type: nil, photo_file_size: nil, photo_updated_at: nil, description: nil> not to be valid

Answer 1

When you create your User instance, the init_items is being called and the Item instances are being created. However, the user's id is not defined at that point, so the user_id value of the created items is nil . This in turn results in the table's user method returning nil in your number_of_items validation.

When you remove the Item validations, then you're RSpec example will fail because you're doing a validation on an Item (ie the result of user3.items.create ) rather than validating the resulting User . Instead, you can do something like this:

user3.items.create(name: "test")
expect(user3).to_not be_valid

Answer 2

I'd avoid using after_initialize . It is called whenever an object is instantiated, even after merely calling User.find . If you must use it, add a test for new_record? so that the items are only added for new User 's.

An alternative approach is to write a builder method to use instead of User.new.

class User < ActiveRecord::Baae
  ITEMS_ALLOWED = 5
  has_many :items

  validates :items, length { is: ITEMS_ALLOWED }

  def self.build_with_items
    new.tap do |user|
      user.init_items
    end
  end

  def init_items
    ITEMS_ALLOWED.times { items.build }
  end
end

describe User do
  context "when built without items" do
    let(:user) { User.new }

    it "is invalid" do
      expect(user.items.size).to eq 0
      expect(user.valid?).to be_false
    end
  end

  context "when built with items" do
    let(:user) { User.build_with_items }

    it "is valid" do
      expect(user.items.size).to eq 5
      expect(user.valid?).to be_true
    end
  end
end

This allows you to separate the item initialization from the user initialization, in case you end up wanting to have a User without items. In my experience, this works out better than requiring all newed up objects to be built the same way. The tradeoff is that you now need to use User.build_with_items in the new action in the controller.