Mongoid: Creating runtime models for embedding

Question

In my app, we have to create models on the runtime, and embed them within the current model. These created models may also in turn embed models. To get some common ground for these embeddable models, I've created a module that can be included into them.

For example:

module CommonMethods
  def make_self(context)
    if context['nested']
      inner_klass_name = context['name'].classify
      inner_klass = Object.const_set(inner_klass_name, Class.new)
      inner_klass.class_eval <<-ENDSRC
        include Mongoid::Document
        include CommonMethods

        embedded_in :#{@mclass_name.underscore}, :inverse_class_name => "#{@mclass_name}"

        after_initialize :start_make_self

        def start_make_self
          @mclass_name = "#{inner_klass_name}"
          make_self(#{context['nested_context']})
        end
      ENDSRC

      self.class_eval <<-ENDSRC
        embeds_one :#{context['name']}, :inverse_class_name => "#{inner_klass_name}"
      ENDSRC
    else
      self.class_eval <<-ENDSRC
        field :#{context['name']}, :type => String
      ENDSRC
    end
  end
end

class MModel
  include Mongoid::Document
  include CommonMethods

  field :context_id, :type => String
  after_initialize :start_make_self

  def start_make_self
    context = Context.where(:uid => self.context_id)
    @mclass_name = "MModel"
    make_self(context.attributes)
  end
end

So, the fields of MModel and its embedded documents are made with help of the Context model.

The problem here is that, while non-nested fields are made, and can be validated on the fly, nested (embedded) models seem to have a problem: they are not initialized when a new MModel is made, and data is passed to it. The first level works, any level below it simply doesn't.

Any hints on this?

score 0 · Answer 1 · answered Aug 02 '12 at 05:38

I solved this issue partially by overriding the constructor for the classes.

class MModel
  include Mongoid::Document
  include CommonMethods

  field :context_id, :type => String

  def initialize(attrs=nil)
    context = Context.where(:uid => attrs[:context_id])
    @mclass_name = "MModel"
    make_self(context.attributes)
    super
  end
end

Similarly for the inner_klass as well. The only issue that remains is that while the relations and validations work (embeds_one, etc), the runtime field declarations don't seem to work. For example, a field declared with type as an Array is not honored. I've worked around it temporarily by providing custom validations for the same.

Mongoid: Creating runtime models for embedding

1 Answers1