Ecto query with case fragment is not casting my enum type correctly

I’m trying to do a grouped count of achievements by using a Postgres CASE statement (I’ll be adding a couple more clauses once I get the query to work), but I’m having trouble with the data casting.

Here’s my query:

from a in Schemas.Achievement,
  where: a.user_id == ^user_id,
         WHEN ? IN (?) THEN 'a'
       END as "type"
       type(^slugs, {:array, AchievementEnum})
     ), count()},
  group_by: fragment("type")

AchievementEnum is a postgres enum type (achievement)

This results in the following error:

[error] Task #PID<0.3036.0> started from #PID<0.2534.0> terminating
** (Postgrex.Error) ERROR 42883 (undefined_function) operator does not exist: achievement = achievement[]

I’m guessing that ecto isn’t sending the list of slugs as a list (so it is sent as achievement instead of achievement[]).

But if I manually put WHEN ? = ('slug1', 'slug2') THEN 'a', it works

Changing the fragment to WHEN ? = ANY(?) THEN 'a' did the trick.

Although I am still interested if anyone has suggested improvements/cleanups.