** (UndefinedFunctionError) function Ch.type/0 is undefined or private.

[JVMartyns]

Repo returns an error when trying to retrieve the subfields of a JSON field using square brackets.
It seems to be an issue with Ecto, but I haven't quite figured out why it's happening yet.
I traced the error back to Ecto's Planner module. Suspect in the validate_json_path! function

How to reproduce:

TestRepo.all(
             from(t in TokenInfoSchema,
               order_by: t.mint,
               select: %{
                 mint: t.mint,
                 name: t.data["nested"]["name"],
                 arr: t.data["nested"]["arr"]
               }
             )
           )

     ** (UndefinedFunctionError) function Ch.type/0 is undefined or private. Did you mean:

         * type/1

     code: assert TestRepo.all(
     stacktrace:
       (ch 0.7.1) Ch.type()
       (elixir 1.19.5) lib/enum.ex:1814: Enum. "-map_reduce/3-lists^mapfoldl/2-0-"/3
       (elixir 1.19.5) lib/enum.ex:1814: Enum."-map_reduce/3-lists^mapfoldl/2-0-"/3
       (elixir 1.19.5) lib/enum.ex:2520: Enum."-reduce/3-lists^foldl/2-0-"/3
       (ecto 3.13.5) lib/ecto/repo/queryable.ex:223: Ecto.Repo.Queryable.execute/4
       (ecto 3.13.5) lib/ecto/repo/queryable.ex:19: Ecto.Repo.Queryable.all/3
       test/ecto/integration/json_test.exs:126: (test)

[ruslandoga]

👋 @JVMartyns

Thank you! I'll add a test with a query like this and would try to debug as well.

[ruslandoga]

The problem seems to be coming from https://github.com/elixir-ecto/ecto/blob/0bc7948ee9fbca21872ef5502f4d4c2c2f3e51f1/lib/ecto/query/planner.ex#L1500 where Ecto drops Ch params info.

It first gets called with

Ecto.Query.Planner.validate_json_path!(["nested", "name"], :data, {:parameterized, {Ch, :json}})

and then

Ecto.Query.Planner.validate_json_path!(["nested", "name"], :data, Ch)

and then Ecto.Type.type(Ch) attempts to call Ch.type().

---

I've opened elixir-ecto/ecto#4723.

---

Just a note that if it's fixed, we still run into problems since we use JSON_QUERY for these nested json path syntax and it's not supported on JSON columns. So we'd need to change that as well to dot syntax or maybe to use either JSON_QUERY or dot syntax based on the type somehow.

[ruslandoga]

👋 @JVMartyns

I think Ch.type/0 issue should now be fixed by #270. I've released the fix as v0.9.0 but

TestRepo.all(
  from(t in TokenInfoSchema,
    order_by: t.mint,
    select: %{
      mint: t.mint,
      name: t.data["nested"]["name"],
      arr: t.data["nested"]["arr"]
    }
  )
)

would still fail due to ecto_ch using JSON_QUERY. Changing that would require extra work so I am not closing this issue.