class Build
  include Mongoid::Document
  has_many :bsuites
end

class Bsuite
  include Mongoid::Document
  belongs_to :build
end

bs = Bsuite.new
bs.build #=> stack level too deep!

resolve:
rename Module: Mongoid::Relations::Accessors#build to Module: Mongoid::Relations::Accessors#*build , also change getter,setter method to use *build

because in Module: Mongoid::Relations::Accessors the self is bs, so call build(name, object.substitutable, metadata) will always return nil.