Inheritance with Mongoid models

Here you can see an example of inheritance using 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, _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 pair will create embedded subdocuments 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.

More examples on CRUD operations will follow in the next chapter.