Implement BSON::DBRef support.

closes #50

Author: nelhage-stripe

lib/mosql/schema.rb

@@ -176,6 +176,8 @@ def transform(ns, obj, schema=nil)
           case v
           when BSON::Binary, BSON::ObjectId, Symbol
             v = v.to_s
+          when BSON::DBRef
+            v = v.object_id.to_s
           when Hash
             v = JSON.dump(v)
           when Array

test/unit/lib/mosql/schema.rb

@@ -170,6 +170,13 @@ class MoSQL::Test::SchemaTest < MoSQL::Test
       assert_equal(["row 1", nil, 'stringy', [1,2,3]], out)
     end
 
+    it 'extracts object ids from a DBRef' do
+      oid = BSON::ObjectId.new
+      out = @map.transform('db.collection', {'_id' => "row 1",
+          'str' => BSON::DBRef.new('db.otherns', oid)})
+      assert_equal(["row 1", nil, oid.to_s, nil], out)
+    end
+
     it 'changes NaN to null in extra_props' do
       out = @map.transform('db.with_extra_props', {'_id' => 7, 'nancy' => 0.0/0.0})
       extra = JSON.parse(out[1])