title: How to create a factory where two objects belong to the same parent?
body: <p>I have the following factory:</p>
  
  <pre><code>factory :user do
      name 'Henk'
      email 'foo@bar.co'
      password 'foobar'
      password_confirmation { |u| u.password }
  end
  
  factory :photo do |ph|
      user
      ph.subtitle 'abc'
      ph.photo { fixture_file_upload( Rails.root.join( 'spec', 'fixtures', 'files', 'test-file-one.png' ), 'image/png') }
  end
  
  factory :ad do |ad|
      user
      name 'Kip'
      reason 'Ik wil gewoon hele mooie nieuwe, om een beetje van te eten.'
      price 69.15
  end
  </code></pre>
  
  <p>Both Photo and Ad belong to a User, however a Photo also belongs to an Ad. This is a problem, because whenever I test the relation between Photo and Add the user validation complains, correctly, that a user with that email is already in use. How do I tell rspec to use that same user again, and not try to create another user with the same factory?</p>