How to use Enum and Custom Scalars together in Absinthe?

Hello, welcome to the forum.

I use simple atoms, without as when I don’t need to use db, like so

  enum :sort_order do
    value :asc
    value :asc_nulls_last
    value :asc_nulls_first
    value :desc
    value :desc_nulls_last
    value :desc_nulls_first
  end

But if You want to persists Int in the DB and keep nice looking status, I would use a scalar. Nothing really complicate, You just need a parse and a serialize functions.

I use this for json.

  scalar :json do
    parse fn input ->
      case Jason.decode(input.value) do
        {:ok, result} -> result
        _ -> :error
      end
    end
    serialize &Jason.encode!/1
  end

And with your Enum requirement, it would be simple to write those 2 functions. For example…

scalar :status do
  parse fn 1 -> :green; 2 -> :yellow; 3 -> :amber; 4 -> :red; _ -> :error end
  serialize fn :green -> 1; :yellow -> 2; :amber -> 3; :red -> 4; _ -> :error end
end

Thanks @kokolegorille! I’m really enjoying Elixir and the forum so far.

Would a scalar be a straight swap out for an enum? From my understanding of your reply it is one or the other and not a way to combine the two.

I tried as per your guidance and am stuck. In my top level schema.ex I took my enum definition of:

  @desc "Current riding status of the trail (defined as an enum)"
  enum :trail_status do
    value :green, as: 1, description: "Green: Clear"
    value :yellow, as: 2, description: "Yellow: Minor Issue"
    value :amber, as: 3, description: "Amber: Significant Issue"
    value :red, as: 4, description: "Red: Major Issue"
  end

and replaced it with your scalar definition (altering it slightly to be trail_status to fit my actual code)

  @desc "Current riding status of the trail (defined as a type)"
  scalar :trail_status do
    parse fn 1 -> :green; 2 -> :yellow; 3 -> :amber; 4 -> :red; _ -> :error end
    serialize fn :green -> 1; :yellow -> 2; :amber -> 3; :red -> 4; _ -> :error end
  end

It probably helps to see my resolver as well…

  def list_trails(%{having_status: status_id}) do
    Trail
    |> where([t], t.status == ^status_id)
    |> Repo.all
  end

Before the switch I was able to run the following query

query {
  trails(havingStatus: GREEN) {
    id
    name
    status
    description
  }
}

It ran without issue and I had the nice constrained/type-ahead completion in GraphiQL that only GREEN, YELLOW, AMBER and RED were allowed.

Now I no longer have the nice type-ahead completion constrained to the valid enum values in GraphiQL but also I’m not able to pass a value to havingStatus: in my query query which results in anything other than an error message saying "Argument \"havingStatus\" has invalid value <VALUE>." where I’ve tried all the following for <VALUE>:

• raw int: 1
• int as string: “1”
• raw values: green, Green, GREEN
• raw values as strings: “green”, “Green”, “GREEN”

With some more experimentation I found out where my issue was with getting an enum to work the way I expected, in my object data type definitions I had missed changing a field from :integer to :trail_status. Once I did that I see values like GREEN in my responses instead of 1 and I was able to even use them in a mutation call.

Something still feels a little off because the enum is defined in the GraphQL schema and it does a nice mapping to integer values in the database schema I was given but if I were to do more complex business logic with conditions on the status of a trail then it seems like I’d want some sort of entity to reflect the trail status – but that could be my OO brain still trying to wrap my head around how to do things in Elixir.

You might want to have a look at EctoEnum, it will probably provide the casting from/to integers in ecto that you are searching for.