fix previous remaining calculation error

[idododu]

when back to previous page, remaining should be total - rs rather than rs - models.length

eg: we have 16 records, and we are on the 2nd page(11 - 16) when click previous btn, rs is equal to 10 since we are moving to records(1 - 10), and models.length is also 10 which cause remaining equals to 0, this happens on sql like select * from user order by name asc, id asc

[olavim]

Thank you for the pull request!

However, this is working as expected. The remaining value should tell you how many results there are remaining in this direction.

---

So, let's say we have 25 items, and we are on the first page, viewing items 0-9 (limit is 10):

• Items 0-9
• Direction is "after"
• Remaining should be 15, because there are 15 more items after this page

go to next page

• Items 10-19
• Direction is "after".
• Remaining should be 5, because there are 5 more items after this page.

go to next page

• Items 20-24
• Direction is "after".
• Remaining should be 0, because there are 0 more items after this page.

go to previous page

• Items 15-24
• Direction is "before".
• Remaining should be 15, because there are 15 more items before this page.

go to previous page

• Items 5-14
• Direction is "before".
• Remaining should be 5, because there are 5 more items before this page.

go to previous page

• Items 0-4
• Direction is "before".
• Remaining should be 0, because there are 0 more items before this page.

---

Could you verify if I understood your problem correctly? The expected behavior is currently documented briefly in https://github.com/olavim/objection-cursor#cursorpagecursor-before. If you think the documentation should be improved, let me know.

[idododu]

in my opinion, if we are visiting the same page, api should return the same pageInfo result no matter the direction is after or before. Otherwise we have to implement direction detect in our codes to calculate start position and end position of current page, which is not convinient. Hope below codes make sense.

// we have 25 records in total

// visit 1st page, api returns below info
const pageInfo = {
  remaining: 15,
  hasNext: true,
  hasPrevious: false,
  total: 25
}

// visit 2nd page, api returns below info
const pageInfo = {
  remaining: 5,
  hasNext: true,
  hasPrevious: true,
  total: 25
}

// when back to the 1st page, api returns below info
const pageInfo = {
  remaining: 0,
  hasNext: true,
  hasPrevious: false,
  total: 25
}

// get current page info
const pagesize = 10
const totalPages = Math.ceil(pageInfo.total / pagesize)

let currentPage
if(pageInfo.remaining == 0) {
  // it is the last page
  currentPage = totalPages
} else {
  /**
   * Here we hope we can use below calculation directly rather
   * currentPage = (pageInfo.total - pageInfo.remaining) / pagesize
   */
  if(direction == 'after') {
    currentPage = (pageInfo.total - pageInfo.remaining) / pagesize
  } else {
    currentPage = totalPages - ((pageInfo.total - pageInfo.remaining) / pagesize)
  }
}

const startPosition = currentPage * pagesize - 9
const endPosition = pageInfo.remaining == 0 ? pageInfo.total : currentPage * pagesize

[olavim]

in my opinion, if we are visiting the same page, api should return the same pageInfo result no matter the direction is after or before.

You might not get the same page info for the same logical page, but unless data has changed, the page info will always be the same for a given cursor. Unless data has changed, an input will give the same output.

But I understand the need for direction detection as it stands. We could deprecate the remaining property and introduce remainingBefore and remainingAfter in its stead. Would this work for you?

[idododu]

forget it.

Do we have any plan to support pagination by current page index rather than cursor?

[olavim]

forget it

I don't understand. remainingBefore and remainingAfter wouldn't solve your problem? I just don't want to change the semantics of remaining, and it's working as I intended it to.

Do we have any plan to support pagination by current page index rather than cursor?

Pagination by page should be well supported by objection already https://vincit.github.io/objection.js/recipes/paging.html#paging.

[olavim]

Features discussed here have been implemented in https://github.com/olavim/objection-cursor/pull/7, together with some additional fixes.