MongoDB中的NumberLong（）&& PHP

db.projects.find()
{ 
  "_id" : ObjectId("508d4028e60d8c2154a2eb36"), 
  "date" : NumberLong(1351432927), 
  "deadline" : "2012-12-31", 
  "payment" : "100500", 
  "title" : "Project", 
  "userid" : ObjectId("5083677d2f5c849509c3aae6") 
}

All right, but in PHP print_r($find_result) doesn't show the key "date" at all!
Why? And how I can extract value from NumberLong() in PHP?