1 var result = db.users.findOne({"name":"Tom Wu"},{"address_ids":1,_id:0})
2 
3 var address = db.address.find({"_id":{"$in":result["address_ids"]}})

{
  "_id":ObjectId("52202135882200383568"),
 "contact":"15074966728" ,
 "dob":"1980-10-18",
  "name":"Tom Wu" ,
  "address_ids":[
      ObjectId("52fff20255863zd616862258"),
      ObjectId("6325846682126886335986") 
    ]    
}