Option for decoding with tagged union values about avrora HOT 7 CLOSED

Hi @LostKobrakai do you have a specific example of when is it needed? I'm trying to keep the library small but functional, so some features definitely not 1:1 with erlavro

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My current case is for permission handling, where a user can have only a single role, but each role has it's own set of additional metadata. I'd like to encode that in a single union of multiple different named records (name == role). That way I'm not encoding the role twice (e.g. in an enum + a separate union of records).

If you don't want to include specific union handling how about a generic way to customize the decoder hook used? This would be even more flexible.

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Since I'm not eating my own dog food anymore, may I ask you to share a made-up example of data and schema that I can take a look at and see what is exactly happening? We can work around to see what could be done to achieve that.

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That's the test I wrote to figure it out. Consider record_1 and record_2 to be role names, and each record can have role specific fields, which might or might not overlap. Not sure if this is actually a good way to compose hooks though.

test "decode with tagged tuple" do
    template = """
    {
      "type": "record",
      "name": "credit_wallet_payment_event",
      "namespace": "io.slim",
      "fields": [
        {
          "name": "record_union",
          "type": [
            {
              "type": "record",
              "name": "record_1",
              "fields": [
                {
                  "name": "start",
                  "type": "int"
                }
              ]
            },
            {
              "type": "record",
              "name": "record_2",
              "fields": [
                {
                  "name": "start",
                  "type": "int"
                }
              ]
            }
          ]
        }
      ]
    }
    """

    {:ok, schema} = Avrora.Schema.Encoder.from_json(template)

    data = %{record_union: {"io.slim.record_2", %{start: 12}}}

    {:ok, payload} = Avrora.Codec.Plain.encode(data, schema: schema)

    opts =
      Map.update!(Avrora.AvroDecoderOptions.options(), :hook, fn avrora_hook ->
        tagged_union_hook = :avro_decoder_hooks.tag_unions()

        fn type, sub_name_or_index, data, decode_fun ->
          tagged_union_hook.(type, sub_name_or_index, data, fn data ->
            avrora_hook.(type, sub_name_or_index, data, decode_fun)
          end)
        end
      end)

    assert %{"record_union" => {"io.slim.record_2", %{"start" => 12}}} ==
             :avro_binary_decoder.decode(payload, schema.full_name, schema.lookup_table, opts)

    assert {:ok, %{"record_union" => %{"start" => 12}}} =
             Avrora.Codec.Plain.decode(payload, schema: schema)
  end

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Hey @LostKobrakai sorry for a long silence, have some IRL things, I will take a look on your example this week and try to share my thoughts

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Evening @LostKobrakai I think I'm back to my nightlife and I've checked the erlavro and its tag union hook. Initially I have no interest to open access to the hook system (I don't have a good usage example), but with your case I think time comes and it makes sense to reconsider.

But instead of opening way to tag unions, I would rather open access to define custom hook which will be called inside of current Avrora.AvroDecoderOptions.__hook__/4 and result will be amended to handle null as nil (same as you did)

And any functionality could be injected (I'm also worried about debugging and will check how can I expose erlavro hooks traces. WDYT?

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Thanks for your help, I really appreciate it, the new configuration option decoder_hook was released as a part of v0.24.0 release 🎉

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