Parent Object In Mongoid Embedded Relation Extensions

Question

Given a simple embedded relationship with an extension like this:

class D
  include Mongoid::Document
  embeds_many :es do
    def m
      #...
    end
  end
end

class E
  include Mongoid::Document
  embedded_in :d
end

You can say things like this:

d = D.find(id)
d.es.m

Inside the extension's m method, how do access the specific d that we're working with?

Answer 1

I'm answering this myself for future reference. If anyone has an official and documented way of doing this, please let me know.

---

After an hour or so of Googling and reading (and re-reading) the Mongoid documentation, I turned to the Mongoid source code. A bit of searching and guesswork lead me to @base and its accessor method base:

  embeds_many :es do
    def m
      base
    end
  end

and then you can say this:

d = D.find(id)
d.es.m.id == id # true

base is documented but the documentation is only there because it is defined using attr_reader :base and documentation generated from attr_reader calls isn't terribly useful. base also works with has_many associations.

---

How did I figure this out? The documentation on extensions mentions @target in an example:

embeds_many :addresses do
  #...
  def chinese
    @target.select { |address| address.country == "China"}
  end
end

@target isn't what we're looking for, @target is the array of embedded documents itself but we want what that array is inside of. A bit of grepping about for @target led me to @base (and the corresponding attr_reader :base calls) and a quick experiment verified that base is what I was looking for.