title: find() and findOne() methods in MongoDB showing different results
body: <p>I have a Mongo database where in the users collection I have just 1 document.
  I do a <code>find()</code> and a <code>findOne()</code> operations using the username filter.
  I get what I think is an incorrect result from <code>find()</code> operation.</p>
  
  <pre><code>MongoDB shell version: 3.2.10
  connecting to: test
  Server has startup warnings: 
  2016-10-20T20:37:32.681-0700 I CONTROL  [initandlisten] 
  2016-10-20T20:37:32.681-0700 I CONTROL  [initandlisten] ** WARNING: /sys/kernel/mm/transparent_hugepage/enabled is 'always'.
  2016-10-20T20:37:32.681-0700 I CONTROL  [initandlisten] **        We suggest setting it to 'never'
  2016-10-20T20:37:32.681-0700 I CONTROL  [initandlisten] 
  2016-10-20T20:37:32.681-0700 I CONTROL  [initandlisten] ** WARNING: /sys/kernel/mm/transparent_hugepage/defrag is 'always'.
  2016-10-20T20:37:32.681-0700 I CONTROL  [initandlisten] **        We suggest setting it to 'never'
  2016-10-20T20:37:32.681-0700 I CONTROL  [initandlisten] 
  &gt; use lab2
  switched to db lab2
  &gt; db.users.find()
  { "_id" : ObjectId("5807ac0765f24dd0660e4332"), "username" : "avtrulzz", "fname" : "Abc", "lname" : "Def", "email" : "test@yahoo.co.in", "password" : "rootuser", "mobile" : NumberLong(1234567890) }
  &gt; db.users.findOne()
  {
      "_id" : ObjectId("5807ac0765f24dd0660e4332"),
      "username" : "avtrulzz",
      "fname" : "Abc",
      "lname" : "Def",
      "email" : "test@yahoo.co.in",
      "password" : "rootuser",
      "mobile" : NumberLong(1234567890)
  }
  &gt; if (db.users.find({username : "noSuchUsername"})) {
  ... print ("Username exists"); 
  ... } else {
  ... print ("User does not exist"); }
  Username exists
  &gt; if (db.users.findOne({username : "noSuchUsername"})) { print ("Username exists");  } else { print ("User does not exist"); }
  User does not exist
  &gt; if (db.users.findOne({username : "avtrulzz"})) { print ("Username exists");  } else { print ("User does not exist"); }
  Username exists
  </code></pre>
  
  <blockquote>
    <p></p>
  </blockquote>
  
  <p>See the <code>find()</code> operation is returning user exists which is not true. <code>findOne()</code> is behaving correctly.<a href="https://i.stack.imgur.com/Q6nIn.png" rel="noreferrer"><img src="https://i.stack.imgur.com/Q6nIn.png" alt="enter image description here"></a></p>