How to set polymorphic relations using Fabricator-gem?

Question

I am trying to setup fabricator-gem to handle my models for testing. The problem I am running into is that it doesn't seem to be able to handle polymorphic relations. I am using MongoDB as my database and Mongoid as my ORM. Consider this example:

class Description
  include Mongoid::Document
  include Mongoid::Timestamps

  embeds_many :images, as: :photo, cascade_callbacks: true
end

class Image
  include Mongoid::Document
  include Mongoid::Timestamps

  embedded_in :photo, polymorphic: true
end

Using this code, you can embed Image documents into many different types of documents, because you set polymorphic: true. This turns out to be a problem when using fabricator, because you would like to do something like this:

Fabricator(:description) do |f|
  f.images(count: 1) { |description, i| Fabricate(:image, photo: description) }
end

But Fabricator-gem automatically assumes there must be a class named Photo. Therefore, when you run your tests, the following error is thrown:

NameError:
       uninitialized constant Photo

How do I tell Fabricator that this is a polymorphic association?

EDIT: Stacktrace Here:

NameError: uninitialized constant PhotoOf
    from /Users/max/.rvm/gems/ruby-1.9.3-p362/gems/activesupport-3.2.11/lib/active_support/inflector/methods.rb:230:in `block in constantize'
    from /Users/max/.rvm/gems/ruby-1.9.3-p362/gems/activesupport-3.2.11/lib/active_support/inflector/methods.rb:229:in `each'
    from /Users/max/.rvm/gems/ruby-1.9.3-p362/gems/activesupport-3.2.11/lib/active_support/inflector/methods.rb:229:in `constantize'
    from /Users/max/.rvm/gems/ruby-1.9.3-p362/gems/activesupport-3.2.11/lib/active_support/core_ext/string/inflections.rb:54:in `constantize'
    from /Users/max/.rvm/gems/ruby-1.9.3-p362/gems/mongoid-3.0.17/lib/mongoid/relations/metadata.rb:602:in `klass'
    from /Users/max/.rvm/gems/ruby-1.9.3-p362/gems/mongoid-3.0.17/lib/mongoid/relations/builders/nested_attributes/one.rb:33:in `build'
    from /Users/max/.rvm/gems/ruby-1.9.3-p362/gems/mongoid-3.0.17/lib/mongoid/attributes/processing.rb:170:in `block in process_relations'
    from /Users/max/.rvm/gems/ruby-1.9.3-p362/gems/mongoid-3.0.17/lib/mongoid/attributes/processing.rb:167:in `each_pair'
    from /Users/max/.rvm/gems/ruby-1.9.3-p362/gems/mongoid-3.0.17/lib/mongoid/attributes/processing.rb:167:in `process_relations'
    from /Users/max/.rvm/gems/ruby-1.9.3-p362/gems/mongoid-3.0.17/lib/mongoid/attributes/processing.rb:153:in `process_pending'
    from /Users/max/.rvm/gems/ruby-1.9.3-p362/gems/mongoid-3.0.17/lib/mongoid/attributes/processing.rb:32:in `block in process_attributes'
    from /Users/max/.rvm/gems/ruby-1.9.3-p362/gems/mongoid-3.0.17/lib/mongoid/attributes/processing.rb:193:in `with_mass_assignment'
    from /Users/max/.rvm/gems/ruby-1.9.3-p362/gems/mongoid-3.0.17/lib/mongoid/attributes/processing.rb:22:in `process_attributes'
    from /Users/max/.rvm/gems/ruby-1.9.3-p362/gems/mongoid-3.0.17/lib/mongoid/document.rb:148:in `block in initialize'
    from /Users/max/.rvm/gems/ruby-1.9.3-p362/gems/mongoid-3.0.17/lib/mongoid/threaded/lifecycle.rb:84:in `_building'
    from /Users/max/.rvm/gems/ruby-1.9.3-p362/gems/mongoid-3.0.17/lib/mongoid/document.rb:143:in `initialize'
... 33 levels...
    from /Users/max/.rvm/gems/ruby-1.9.3-p362/gems/fabrication-2.5.4/lib/fabrication/generator/base.rb:91:in `block in process_attributes'
    from /Users/max/.rvm/gems/ruby-1.9.3-p362/gems/fabrication-2.5.4/lib/fabrication/generator/base.rb:90:in `each'
    from /Users/max/.rvm/gems/ruby-1.9.3-p362/gems/fabrication-2.5.4/lib/fabrication/generator/base.rb:90:in `process_attributes'
    from /Users/max/.rvm/gems/ruby-1.9.3-p362/gems/fabrication-2.5.4/lib/fabrication/generator/base.rb:6:in `build'
    from /Users/max/.rvm/gems/ruby-1.9.3-p362/gems/fabrication-2.5.4/lib/fabrication/generator/base.rb:26:in `create'
    from /Users/max/.rvm/gems/ruby-1.9.3-p362/gems/fabrication-2.5.4/lib/fabrication/schematic/definition.rb:62:in `block in fabricate'
    from /Users/max/.rvm/gems/ruby-1.9.3-p362/gems/fabrication-2.5.4/lib/fabrication/schematic/definition.rb:61:in `instance_eval'
    from /Users/max/.rvm/gems/ruby-1.9.3-p362/gems/fabrication-2.5.4/lib/fabrication/schematic/definition.rb:61:in `fabricate'
    from /Users/max/.rvm/gems/ruby-1.9.3-p362/gems/fabrication-2.5.4/lib/fabrication/fabricator.rb:10:in `fabricate'
    from /Users/max/.rvm/gems/ruby-1.9.3-p362/gems/fabrication-2.5.4/lib/fabrication.rb:51:in `Fabricate'
    from (irb):1
    from /Users/max/.rvm/gems/ruby-1.9.3-p362/gems/railties-3.2.11/lib/rails/commands/console.rb:47:in `start'
    from /Users/max/.rvm/gems/ruby-1.9.3-p362/gems/railties-3.2.11/lib/rails/commands/console.rb:8:in `start'
    from /Users/max/.rvm/gems/ruby-1.9.3-p362/gems/railties-3.2.11/lib/rails/commands.rb:41:in `<top (required)>'
    from script/rails:6:in `require'
    from script/rails:6:in `<main>'

Answer 1

I think the issue is actually with how you defined your embeds_many association. Try removing the "as" option completely and see if that fixes the issue.

class Description
  include Mongoid::Document
  include Mongoid::Timestamps

  embeds_many :images, cascade_callbacks: true
end

class Image
  include Mongoid::Document
  include Mongoid::Timestamps

  embedded_in :photo, polymorphic: true
end

Fabrication doesn't attempt to turn attribute names to classes. As long as you have a Fabricator(:image) defined, preferably without the photo association in it, then you should just be able to do this:

Fabricator(:description) do
  images(count: 1)
end