title: Mongoose populate single item in array
body: <p>I have a model that has an array of dynamic references.</p>
  
  <pre><code>var postSchema = new Schema({
    name: String,
    targets: [{
      kind: String,
      item: { type: ObjectId, refPath: 'targets.kind' }
    }]
  }); 
  </code></pre>
  
  <p>I am using the targets property to store references to multiple different models, users, thread, attachments, etc.</p>
  
  <p>Is it possible to populate only the references that I want?</p>
  
  <pre><code>Post.find({}).populate({
    // Does not work
    // match: { 'targets.kind': 'Thread' }, // I want to populate only the references that match. ex: Thread, User, Attachment
    path: 'targets.item',
    model: 'targets.kind',
    select: '_id title',
  });
  </code></pre>
  
  <p>Thanks</p>