Can't do geo query on embedded document using Mongoid and Geocoder - ruby-on-rails

Question

(Ruby 1.9.3, MongoDB 2.0.4, Rails 3.2, Mongoid 2.4, Geocoder 1.1.1)
I have the following models:
class Company
include Mongoid::Document
embeds_one :office
index [[ "office.coordinates", Mongo::GEO2D ]]
end
class Office
include Mongoid::Document
include Geocoder::Model::Mongoid
geocoded_by :address
field :city, :type => String
field :state, :type => String
field :coordinates, :type => Array
embedded_in :company
after_validation :geocode
def address
"#{city}, #{state}"
end
end
I do this in the console:
> c = Company.new
=> #<Company _id: 4f885aa56d20f03898000003, _type: nil>
> c.office = Office.new(:city => "San Francisco", :state => "CA")
=> #<Office _id: 4f885ab66d20f03898000004, _type: nil, city: "San Francisco", state: "CA", coordinates: nil>
> c.save
=> true
So far so good. But then I try to retrieve the company by doing a geoquery on its embedded document (office):
> Company.where(:office.near => Company.first.office.to_coordinates).first
Mongo::OperationFailure: can't find special index: 2d for: { office: { $near: [ -122.4194155, 37.7749295 ] } }
from /Users/raphael/.rvm/gems/ruby-1.9.3-p125/gems/mongo-1.6.2/lib/mongo/cursor.rb:144:in `next'
from /Users/raphael/.rvm/gems/ruby-1.9.3-p125/gems/mongo-1.6.2/lib/mongo/collection.rb:288:in `find_one'
from /Users/raphael/.rvm/gems/ruby-1.9.3-p125/gems/mongoid-2.4.8/lib/mongoid/collections/master.rb:25:in `block in find_one'
from /Users/raphael/.rvm/gems/ruby-1.9.3-p125/gems/mongoid-2.4.8/lib/mongoid/collections/retry.rb:29:in `retry_on_connection_failure'
from /Users/raphael/.rvm/gems/ruby-1.9.3-p125/gems/mongoid-2.4.8/lib/mongoid/collections/master.rb:24:in `find_one'
from /Users/raphael/.rvm/gems/ruby-1.9.3-p125/gems/mongoid-2.4.8/lib/mongoid/collection.rb:60:in `find_one'
from /Users/raphael/.rvm/gems/ruby-1.9.3-p125/gems/mongoid-2.4.8/lib/mongoid/contexts/mongo.rb:203:in `first'
from /Users/raphael/.rvm/gems/ruby-1.9.3-p125/gems/mongoid-2.4.8/lib/mongoid/criteria.rb:45:in `first'
from (irb):2
from /Users/raphael/.rvm/gems/ruby-1.9.3-p125/gems/railties-3.2.3/lib/rails/commands/console.rb:47:in `start'
from /Users/raphael/.rvm/gems/ruby-1.9.3-p125/gems/railties-3.2.3/lib/rails/commands/console.rb:8:in `start'
from /Users/raphael/.rvm/gems/ruby-1.9.3-p125/gems/railties-3.2.3/lib/rails/commands.rb:41:in `<top (required)>'
from script/rails:6:in `require'
from script/rails:6:in `<main>'
What am I doing wrong? I've run rake db:mongoid:create_indexes.

Answer 1

You need to run the query against the embedded field:
Company.where(:'office.coordinates'.near => Company.first.office.to_coordinates).first
If you want to leverage the near scope created by the geocoder gem under Office, you can do something like the following:
# in Company.rb
self.near(office, radius = 20, conditions = {})
self.where(conditions).tap do |criteria|
near_criteria = Office.scopes[:near].conditions.call(office, radius)
criteria.selector[:'office.coordinates'] = near_criteria.selector[:coordinates]
end
end
This creates Company#near which takes an Office object. It will inject the query created by the Office#near scope into a query for a company.