fix bug last_page? wrong when current_page is 1 and total_pages is 0 (version 1.0.1)

[HoangQuan]

I found a bug when when current_page is 1 and total_pages is 0 (There last page is also last page in this case)
When I tried to query like this: User.where(id: 'not_exist').page(1).per(10)
Then last_page? is false But it's should be true.
Please review and comfirm if I am correct. thanks

[yuki24]

Could you elaborate? Theoretically User.where(id: 'not_exist').page(1).per(10) (is this just an example?) would always return 0 and doesn't make sense to use it in production. There is of course a case where there is no record in the table you are trying to load data from, but it's an edge case and I'm typically not concerned about such a case.

[HoangQuan]

@yuki24 , Thank you very much for your replied
In my case, I write an API that check and update the page and display_next_button using last_page? like that:

result[:display_next_button] = false
unless users.last_page?
  result[:page] += 1 
  result[:display_next_button] = true
end

There are 2 scenario below:
1, page = 1 and users has no record. Then total_pages is 0 (as I commented above)
-> In this case my result[:page] is increase and the display_next_button is displayed but It's wrong
2, Suppose that the total_pages is 10 but someone request to server with params[:page] = 11
-> Then the page is increase too, and the display_next_button is still displaying.

How do you think about those two cases?
I don't think it's an edge case.

[sanemat]

This is my case.

#controller
@entries = Entry.where()... #=> Entry.none

#view
json = {}
json[:_links] = {}
json[:_links][:self] = { href: entries_url(page: @entries.current_page, limit: @entries.limit_value) }
json[:_links][:prev] = { href: entries_url(page: @entries.prev_page, limit: @entries.limit_value) } unless @entries.first_page?
json[:_links][:next] = { href: entries_url(page: @entries.next_page, limit: @entries.limit_value) } unless @entries.last_page?

I should use #exists??

json[:_links][:next] = { href: entries_url(page: @entries.next_page, limit: @entries.limit_value) } if @entries.exists? && !@entries.last_page?

[HoangQuan]

@sanemat In your case, I think we only need next_page

json[:_links][:next] = { href: entries_url(page: @entries.next_page, limit: @entries.limit_value) } if @entries.next_page

because @entries.next_page will return number when next_page is exist and return nil if it's not.
Can you try it and comfirm?
anw, I want to use @entries.last_page? but there are some problem as I commented above.

[yuki24]

It seems that you could just the out_of_range? method. Keep in mind that we may deprecate the out_of_range? method since it behaves exactly like the empty? method.

if !users.last_page? || !users.out_of_range?
  result[:page] += 1
  result[:display_next_button] = true
end

Please also have a look at the paginator template for how you could show/hide pagination links. I would also recommend implementing RFC5988 rather than passing flags and page numbers around. I'm not sure about your codebase but I have a hunch that there's a better way of showing a link to the next page.

[yuki24]

I don't think we should change this since this is mathematically incorrect.

[HoangQuan]

@yuki24 Thank you for corrected me.

[yuki24]

I'm closing this issue since kaminari used to behave exactly like the proposed behavior before. Thanks!

[To1ne]

Apparently this is the intended behavior, see #583.

[HoangQuan]

thank you for the information (y)