【问Mongoose】我应该如何处理分页？

// 获取列表-不分组

const getBooks = async (ctx, next) => {

  let { size = 10, page = 1 } = ctx.query

  let optiOns= {

    skip: Number((page - 1) * size),

    limit: Number(size)

  }

  let res = await Book.find({}, null, options)

  let total = await Book.countDocuments()

  let data = {

    list: res,

    pagination: {

      total,

      page,

      size

    }

  }

  ctx.body = {

    data,

    code: 0

  }

}

// 获取列表-如何分组

const getMyBooks = async (ctx, next) => {

  let authorId = ctx.authorId

  let { size = 10, page = 1 } = ctx.query

  let optiOns= {

    skip: Number((page - 1) * size),

    limit: Number(size)

  }

  let res = await Book.find({ author: authorId }, null, options)

  // ???????????

  let total = await Book.countDocuments() // 这个总数应该如何获取比较好？是按authorId查到全部的book，取数组length么？

  let data = {

    list: res,

    pagination: {

      total,

      page,

      size

    }

  }

  ctx.body = {

    data,

    code: 0

  }

}