如何从 mongodb 获取最后 10 条消息？

Question

In my project has some chat module. I need to create request for every N messages. How correctly create request in frontend-node-mongo. For example I got 10 last messages and scroll up for watching previous messages, how can I skip them and get next 5 messages? Now I get all messages without limit.

Node

router.get(
  '/messages',
  async (req, res) => {
    try {
      const {user, destination} = req.query
      let userFrom = await User.findOne({email: user})
      let userTo = await User.findOne({email: destination})
      let messages = await Message.find({
        $or: [{senderId: userFrom, recipientId: userTo}, {senderId: userTo, recipientId: userFrom}]
      })
      return messages ? res.status(200).json(messages) : res.status(204)
    } catch (e) {
      res.status(500).json({message: "Error"})
    }
  })

Answer 1

With mongoose model, you can use pipe functions like skip and limit for pagination.

Message.find({criteria}).skip(number_of_records_to_skip).limit(number_of_records_to_fetch)

Just calculate, based on your page size on UI, how much you need to skip, and pass this via query parameter to the backend. And for complete pagination with mongoose solution just search the net or stackoverflow. Here is one: Mongoose pagination from server side

Answer 2

I suppose you are already calculating the limit (Number of records to display) and skip (Number of records to skip).

You can simply use the aggregate pipeline as below.

let aggregatePipelines = [
    {
        $match: {
            $or: [
                {
                    senderId: userFrom,
                    recipientId: userTo
                },
                {
                    senderId: userTo,
                    recipientId: userFrom
                }
            ]
        }
    }
]

if (skip != 0)
    aggregatePipline.push({ $skip: skip });

if (pageLimit != 0)
    aggregatePipline.push({ $limit: pageLimit });

let messages = await Message.aggregate(aggregatePipelines);

The above query will simply return all the records if skip and limit are not specified.