default enums avro

[LiorPel]

while I did see in the code source that default is not allowed for enums in avro. this presents a big issue with backward compatibly between versions.
If I decide to add any new required field a next version of the schema, a new enum field in the contract would fail the backwards compatibly check unless not required

[jochenchrist]

Are we talking about avro export or avro testing?

Can you make an example what you would like to have in avro?

[SabineGl]

Hi @jochenchrist ! I have the same issue and here is an example:

this is translated correctly:

{
  "name": "sadaType",
  "type": {
    "type": "enum",
    "name": "SadaType",
    "symbols": ["customer", "prospect", "churn"]
  }
}

into:

sadaType:
  title: SadaType
  type: string
  required: true
  enum:
    - customer
    - prospect
    - churn
  config:
    avroType: enum

BUT this here is not:

{
  "name": "customerAccountCodeType",
  "type": [
    "null",
    {
      "type": "enum",
      "name": "CodeType",
      "symbols": ["bscs", "backoffice", "tmsp"]
    }
  ],
  "default": null
}

It looks like this after importing avro to data contract:

customerAccountCodeType:
  type: string
  required: false

I asked chat CPT --> I got this :-)

So what's the difference?
🔹 1. The type is wrapped in a union (["null", enum]) in Case 2
The main difference is:

Case 1: pure enum type

Case 2: union of null and enum, i.e., optional enum

This union structure causes many Avro parsers (including datacontract-cli) to lose track of the inner enum metadata, unless they explicitly handle unioned complex types.

🔹 2. The default value null makes it optional, which some tools interpret as "non-enum"
The default: null and ["null", {...}] imply that the field is nullable — some tools interpret this as a generic optional string, and don't descend into the union to inspect the enum type properly.

✅ How to Fix It
You have a few options:

🔧 Option 1: Improve your tool’s parsing logic (if you control it)
You could patch or extend the logic in datacontract-cli to detect when:

"type": ["null", { "type": "enum", ... }]

...and still preserve the enum type in the YAML output. This is technically correct and should be supported.

Can this be fixed soon? :-)

Thx!

[jochenchrist]

@SabineGl and @LiorPel I prepared PR $843. Would you like to review it?

[SabineGl]

thanks a lot, @jochenchrist! I would like too but I’m currently on vacation and can’t manage right away. I will forward it to my colleagues 😀