Required files
mongoid/relations/builder
mongoid/relations/nested_builder
mongoid/relations/builders/embedded/in
mongoid/relations/builders/embedded/many
mongoid/relations/builders/embedded/one
mongoid/relations/builders/nested_attributes/one
mongoid/relations/builders/nested_attributes/many
mongoid/relations/builders/referenced/in
mongoid/relations/builders/referenced/many
mongoid/relations/builders/referenced/many_to_many
mongoid/relations/builders/referenced/one