title: How to build an $in query of ObjectIds using QueryBuilder with MongoDB
body: <p>I am trying to build an $in query with QueryBuilder (MongoDB Java API 2.9.1).  I have no problem when the query is an array of strings but when I try with an array of ObjectIds it doesn't work (returns nothing).</p>
  
  <p>I am able to run the query successfully and get a result from the console:</p>
  
  <p>Query in console:
  db.collection.find({removed:false,app_id: {$in : [ObjectId("4f75c533ac99d845186e19b2"), ObjectId("4f75c533ac99d845186e19b3")]}})</p>
  
  <p>Query created by QueryBuilder (MongoDB Java API 2.9.1):</p>
  
  <p>Object[] ids;</p>
  
  <p>Java code:
  DBObject query = QueryBuilder.start("app_id").in(ids).and("removed").is(false).get();</p>
  
  <p>ToString on DBObject produces:
  { "app_id" : { "$in" : [ { "$oid" : "4f75c533ac99d845186e19b2"}]} , "removed" : false}</p>
  
  <p>Not sure if I am doing something wrong or the API doesn't support and $in query of type ObjectId.  Any ideas? </p>