Question

Is there a way to pass a BSON object directly into the .find() in the mongo-ruby-driver?

At the moment I have a basic sinatra app that takes URL encoded JSON and parses it into the .find() but I would ideally like to give it straight BSON:

require 'sinatra'
require 'mongo'
require 'json'

include Mongo
db = MongoClient.new().db('test')

get '/' do
  if request[:query]
    query = JSON.parse(CGI::unescape(request[:query]))
    db.collection('test_collection').find(query).to_a.to_json
  end
end

So essentially have something along the lines of BSON.parse(url-encoded-query) and be able to pass that into a .find() returning the result.

Example URL: http://localhost:4567/?query=%7B%20%22name%22%20%3A%20%22john%20doe%22%20%7D
Current query: { "name" : "john doe" }
BSON query: { name: /.*john.*/, interests: [ 'fishing', 'golf' ]} that I’d like to work

Answer 1

The following test script demonstrates how to use the $elemMatch operator as a projection. Please note that the Collection#find method takes arbitrary documents for both the “selector” formal parameter and for the “opts” :fields option.

MongoDB documents are mapped to/from Ruby Hash objects, and these documents can fully incorporate MongoDB operators.

elemmatch_projection.rb

#!/usr/bin/env ruby

# Ruby translation of example from http://docs.mongodb.org/manual/reference/projection/elemMatch/
require 'mongo'
coll = Mongo::MongoClient.new['test']['students']
coll.remove
coll.insert({
  zipcode: 63109,
  dependents: [
    { name: "john", school: 102, age: 10 },
    { name: "jess", school: 102, age: 11 },
    { name: "jeff", school: 108, age: 15 }
  ]
})
p coll.find( { zipcode: 63109 }, :fields => { dependents: { '$elemMatch' => { school: 102 } } } ).to_a

ruby elemmatch_projection.rb

[{"_id"=>BSON::ObjectId('50eab29929daeb05ae000001'), "dependents"=>[{"name"=>"john", "school"=>102, "age"=>10}]}]

This is another answer because the question has been significantly clarified by the OP.

Hope that this helps you understand how to use MongoDB documents and operators in Ruby.