title: how to use populate and aggregate in same statement?
body: <p>This is my appointment collection:</p>
  
  <pre><code>{ _id: ObjectId("518ee0bc9be1909012000002"), date: ISODate("2013-05-13T22:00:00Z"), patient:ObjectId("518ee0bc9be1909012000002") }
  
  { _id: ObjectId("518ee0bc9be1909012000002"), date: ISODate("2013-05-13T22:00:00Z"), patient:ObjectId("518ee0bc9be1909012000002") }
  
  { _id: ObjectId("518ee0bc9be1909012000002"), date: ISODate("2013-05-13T22:00:00Z"), patient:ObjectId("518ee0bc9be1909012000002") }
  </code></pre>
  
  <p>I used aggregate to get the following result</p>
  
  <pre><code>{date: ISODate("2013-05-13T22:00:00Z"),
  patients:[ObjectId("518ee0bc9be1909012000002"),ObjectId("518ee0bc9be1909012000002"),ObjectId("518ee0bc9be1909012000002")] }
  </code></pre>
  
  <p>like this:</p>
  
  <pre><code>Appointments.aggregate([
  {$group: {_id: '$date', patients: {$push: '$patient'}}},
  {$project: {date: '$_id', patients: 1, _id: 0}}
  ], ...)
  </code></pre>
  
  <p>How can I populate the patient document
  I trued this but it doesn't work ... <code>Appointments.find({}).populate("patient").aggregate</code>....</p>
  
  <p>In other words, can i use populate and aggregate at the same statement</p>
  
  <p>any help please</p>