activerecord and mongo / mongo-mapper bridge

Question

I have a project which I have used Active Record and which I'd like to add some new features using MongoDB. Rather than re-invent the wheel and re-write my entire site, how can I integrate 2 models together, one which use MongoMapper and the other ActiveRecord (postgres).

I've found that others have done it successfully, but no examples:

http://groups.google.com/group/mongomapper/browse_thread/thread/ec5ad00e18e7dd2c/887b8b0b904a8f73?lnk=gst&q=activerecord#887b8b0b904a8f73

For example, I have an STI Mongo model(s) of Places which I want to relate to an existing ActiveRecord model of Locations... ie Cities. and a User model based on Authlogic... how can I use them in concert? I'd be grateful for a pointer or two in the right direction.

Thanks,

Answer 1

This worked beautifully

places model

  key :location_id, Integer, :required => true

    def location
        Location.find(location_id)
    end

locations model

  def self.find_places(id)
    Property.find_by_location_id(id)
  end

  def find_places
    Property.find_by_location_id(id)
  end

Answer 2

You can also use typecasting.

Instead of just storing the location_id in mongodb, you can implement to class methods, from_mongo and to_mongo, in the Location class to allow mongomapper to serialize each Location instance in a mongo safe-and-friendly manner.

Simple(istc) example:

Places model

key :location, Location, :required => true

Location model

def self.to_mongo(location)
  location[:id]
end

def self.from_mongo(location_id)
  find(location_id)
end

This, of course, is exactly the same example as in the previous answer. The cool thing here is that you can serialize a full string, with more data if needed, thus making it easier to query and retrieve data from mongo.

For instance, the location_id and coordinates, so you can mimic a geodb and map/reduce for places in the same latitude. (stupid example, I know)

Reference: More MongoMapper Awesomenes