dncuug/X.PagedList

Document that you have to order your IQueryable

GeeWee opened this issue · 2 comments

GeeWee commented

Is your feature request related to a problem? Please describe.
In the documentation you simply pass an IQueryable to the PagedList without any sort of keyselector. However if you e.g. pass an IQueryable from a database without any keyselector, then the results aren't guaranteed.

The generated SQL (For sql server) is as follows

SELECT [a].[WtgId], [a].[TimeOnUtc], [a].[Code], [a].[AlarmType], [a].[Controller], [a].[Guid], [a].[SourceId], [a].[StationId], [a].[Text], [a].[TimeOffLocal], [a].[TimeOffUtc], [a].[TimeOnLocal], [a].[Vendor], [a].[VendorData], [a].[Version], [a].[WindFarmId]
FROM [alarms] AS [a]
ORDER BY (SELECT 1)
OFFSET @__p_0 ROWS FETCH NEXT @__p_0 ROWS ONLY

where ORDER BY (SELECT 1) doesn't actually enforce any ordering.

This means that if I use the same queryable multiple times, the results are non-deterministic. As the paginated list just seems to use skip & take, this means that the paginated list will be out of order, and you can get duplicated values while paginating through.

I think a keyselector should be forced if you don't pass in an IOrderedQueryable, so we're sure that we always have a working pagination.

axtox commented

maybe you should force orderby in your library when creating paginglist just before skip and take? is there any concerns doing so? it will actually fix the problem