mongodb - Problem using then after mongoose save operation

Question

This is my save operation, but the output order of the print statements is
B: undefined A: 正确内容

router.post('/reply', (req, res, next) => {
  let topic_id = req.body.topic_id,
      content  = req.body.content

  let replyEntity = new replyModel({
    author: req._id,
    topic: topic_id,
    content
  })
  replyEntity.save((err, _new_reply) => {
    if (err) {
      return res.json({
        status: -1
      })
    }
    console.log('A: '+_new_reply)
    return _new_reply
  })
  .then((reply) => {
    console.log('B:  '+reply)
    return res.json({
      status: 0
    })
  })
})

Why is the then operation executed first? Shouldn’t it be executed after my save promise returns?
I have specified mongoose.Promise = Promise;
I hope someone can help me solve it = =

Answer 1

You got it mixed up,

 replyEntity.save((err, _new_reply) => {
    if (err) {
      return res.json({
        status: -1
      })
    }
    console.log('A: '+_new_reply)
    return _new_reply
  })
  .then((reply) => {
    console.log('B:  '+reply)
    return res.json({
      status: 0
    })
  })
})

You put callback and promise together

Link description

Answer 2

Use return Promise.resolve(_new_replay) after successful save, do not return directly