t = db.factories
t.drop()
t.insert( { name: "xyz", metro: { city: "New York", state: "NY" } } )
t.ensureIndex( { metro : 1 } )

assert( db.factories.find().count() )

assert.eq( 1, db.factories.find( { metro: { city: "New York", state: "NY" } } )
                          .hint({metro: 1})
                          .count() )

assert.eq( 1, db.factories.find( { metro: { $gte : { city: "New York" } } } )
                          .hint({metro: 1})
                          .count() )