Question: backwards paging

[bart-degreed]

Description

Recently IPageService.Backwards was introduced. As I'm implementing my own paging (via Elasticsearch), I wonder what this is intended for and how it can be used.

It would allow for a URL like /api/users?page[number]=-5, but what does that mean? My first thought was to interpret it as "5 pages back from the current position". But the absolute page offset is 1, unless specified explicitly in the url, which would defeat the purpose of having a relative offset.
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Environment

latest master branch

[wisepotato]

AFAIK this fails, and if it does, it would be "n-5"th page. @maurei ?

[maurei]

Backward paging is supported. Effectively it means pagination starts at the end of a result set and moves "backwards" from there, as opposed from moving forward at the beginning of a result set.

Example: Assume n resources with id 1 till n which by default are returned all at once ordered by id , i.e. schematically: { 1 }, { 2 } ... { n -1 }, { n }.

"Normal" forward paging would yield

• for the first page the set { 1 } ... { 10 }, and
• for the third page the set { 21 } ... { 30 }.

Backward paging would start at the end. It would field

• for the first backward page (page[number]=-1) the set { n } ... { n-9 }, and
• for the third backward page (-3) the set { n-20 } ... { n-29 }

Note: the page numbers are based-1, so there is no zero-th page.

"5 pages back from the current position"

Request scopes are stateless: there is no connection between different request scopes. As such there is no such thing as a "current position" relative to a preview request. The requested position is always specified by the client by including the page number (where omitting that parameter implies the first page)

Let me know if that answers your question

[maurei]

See also these functional tests

[bart-degreed]

Interesting. So it actually reverses the order of all individual items, instead of specifying an offset that is relative from the last page number. Thanks for the thorough explanation!

[bart-degreed]

So this is identical to sorting in descending order, right?