t = db.find7;
t.drop();

x = { "_id" : { "d" : 3649, "w" : "signed" }, "u" : { "3649" : 5 } };
t.insert(x );
assert.eq( x , t.findOne() , "A1" );
assert.eq( x , t.findOne( { _id : x._id } ) , "A2" );