填充'；s使用mongoose填充的ID数组

我有一个像这样的对象：

Topic
 {
    "posts": [
        "5baabfeb87a1401432791534",
        "5bac21814a0f9a2262a77f1b"
    ],
    "_id": "5ba06e74dbc05f039490438c",
    "topic": "new topic",
    "description": "this is the description",
    "date": "2018-09-18T03:18:12.062Z",
    "__v": 2
}

我正在尝试使用mongoose的populate将Topic.posts作为记录数组返回。这就是我正在尝试的

router.get('/:topicId/posts', (req,res) => {
  const {topicId} = req.params
  Topic.findById(topicId)
  .then(topic => res.json(topic.posts.populate('posts')) 
     )
  .catch(err => res.send(err))
});
//getting a {} blank object its not even an array?

如果可能，我希望它返回整个主题对象，并填充数组

Topic
  {
    "posts": [
        {
        "_id": "5bac21814a0f9a2262a77f1b",
         "post": "post 2",
         "description": "blah blah",
        },
        {
          "_id": "5baabfeb87a1401432791534",
           "post": " this is a post",
           "description": "blah blah blah"
          }
    ],
    "_id": "5ba06e74dbc05f039490438c",
    "topic": "new topic",
    "description": "this is the description",
    "date": "2018-09-18T03:18:12.062Z",
    "__v": 2
}

我的选择是什么？

找到了答案

router.get('/:topicId/posts', (req,res) => {
  const {topicId} = req.params
  Topic.findById(topicId) //I thought you had to map the array but populate iterates for you
  .populate('posts')
  .then(topic => res.json(topic))
  .catch(err => res.send(err))
});