Backfill data page - question on "next_page = results |> Enum.reverse() |> List.first()"

[lovebes]

Hi, in https://fly.io/phoenix-files/backfilling-data/#batching-deterministic-data - The code in getting the next_page id, this seems to imply that Repo.update_all would return the results in an ordered list, and in reversed order.

Would that be true? I wonder if you'd need to do some sorting on the result to get the tail of the result?

[dbernheisel]

That's a good catch! I suspect adding an order during update could make it deterministic, otherwise sorting application-side is fine too.

[lovebes]

Ah thanks for confirming! Would it be possible to edit the example in the article? The migration series of articles is imho a very important document that I refer to time and time again at work. Really appreciate the work put into the article!!

[dbernheisel]

Will do!

[dbernheisel]

I haven't forgotten about this. FWIW, I think adding a CTE to ensure order is the right solution (or sorting Elixir-side), just need to write the example and test it.

[lovebes]

@dbernheisel no worries thank you!
Really appreciate ThinkingElixir podcast and thanks for all the time and effort to bring quality news about Elixir to the listeners! 👍