The following code is an example of inheritance using the Mongoid models:

class Canvas
  include Mongoid::Document
  field :name, type: String
  embeds_many :shapes
end

class Shape
  include Mongoid::Document
  field :x, type: Integer
  field :y, type: Integer
  embedded_in :canvas
end
 
class Circle < Shape
  field :radius, type: Float
end
 
class Rectangle < Shape
  field :width, type: Float
  field :height, type: Float
end

Now, we have a Canvas class with many Shape objects embedded in it. Mongoid will automatically create a field, which is _type, to distinguish between parent and child node fields. In scenarios where documents are inherited from their fields, relationships, validations, and scopes get copied down into their child documents, but not vice-versa.

embeds_many and embedded_in pairs will create embedded sub-documents to store the relationships. If we want to store these via referencing to ObjectId, we can do so by substituting these with has_many and belongs_to.