Using actor_id in atomic Change causes sql error

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Hey there I’m giving Ash my first try and like it pretty well so far. I’m trying to implement a bulk update but run into a SQL error and I can only guess the problem. I have the following Change, similar to the one in the book:

defmodule CourseManager.Chat.Changes.AddUserToSeenBy do use Ash.Resource.Change @impl true def init(opts), do: {:ok, opts} @impl true def atomic(_changeset, _opts, context) do if context.actor do actor_id = context.actor.id {:atomic, %{ seen_by: {:atomic, expr( fragment( "array_prepend(?, array_remove(?, ?))", ^actor_id, seen_by, ^actor_id ) )} }} else :ok end end end

And the attribute:

 attribute :seen_by, {:array, :uuid} do description "Array of user IDs who have seen this message" default [] public? true end

The bulk_update didn’t work, so I tried a single update, but I get the following error:

[debug] QUERY ERROR source="messages" db=1.5ms queue=0.3ms idle=25.3ms UPDATE "messages" AS m0 SET "updated_at" = (CASE WHEN (array_prepend($1, array_remove(m0."seen_by"::uuid[], $2)))::uuid[] != m0."seen_by"::uuid[] THEN $3::timestamp ELSE m0."updated_at"::timestamp END)::timestamp, "seen_by" = (array_prepend($4, array_remove(m0."seen_by"::uuid[], $5)))::uuid[] WHERE (m0."id"::uuid = $6::uuid) RETURNING m0."id", m0."message", m0."deleted", m0."reactions", m0."seen_by", m0."inserted_at", m0."updated_at", m0."user_id", m0."course_id", m0."parent_message_id" ["71a3f79a-62f6-49c3-8c43-d7d82ab6fd1c", "71a3f79a-62f6-49c3-8c43-d7d82ab6fd1c", ~U[2025-07-28 16:35:28.369137Z], "71a3f79a-62f6-49c3-8c43-d7d82ab6fd1c", "71a3f79a-62f6-49c3-8c43-d7d82ab6fd1c", "b6a170f6-0373-460f-acef-77ae9e76bb72"]

When I put the query in pgadmin and applying the arguments, I only have to use single quotes to make it work correctly.

Is it possible that the PG typecheck fails because the actor_id is not passed as a uuid but as a string instead?
Can anyone give me some advice how to proceed?

Thanks

2

Hmm…it could be related to that. You don’t see any other errors? Something you can try as an experiment is transforming the actor_id to a binary before providing it. Or you could try:

type(^actor_id, :uuid) in place of just referencing the actor id.

3

Amazing, thanks very much :face_blowing_a_kiss:. It did the trick.

 fragment( "array_prepend(?, array_remove(?, ?))", type(^actor_id, :uuid), seen_by, type(^actor_id, :uuid) )
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