Default values support in codegen about dotnet-avro HOT 5 OPEN

Sorry for the late reply, I've been sidetracked away from Avro these last few days.
I've got 2 possible suggestions:

1. Handle the "happy" path only, if the default value is null of a scalar, generate the [DefaultValue] attribute correctly. If we're not in a supported scenario, issue a warning and don't produce anything.
2. For the unsupported case like the one you highlighted above, still issue a warning, but decorate the property with a new attribute [DefaultSchemaValueJson], which reproduce the default value as it is defined in the originating schema, and is used when producing the schema from the record class.

Option 1 would be good enough for most cases, and would be enough to ensure we have a good story when one team generate a schema from C# code, and another team wants to produce a C# class from that same schema. The 2nd team would be able to used that class without new, potentially incompatible schemas being published to the registry.

Option 2 would even push this further by allowing a producer to handle schemas that don't come from a generated C# class.

from dotnet-avro.

This would be nice to have, but I’m not sure what we’d do when the default value couldn’t be expressed as a constant. For instance, with a (contrived) schema:

{
  "type": "record",
  "name": "MyRecord",
  "fields": [
    {
      "name": "Value",
      "type": [
        "MyRecord",
        "null"
      ],
      "default": {
        "MyRecord": {
          "Value": null
        }
      }
    }
  ]
}

the code generator would try to express that as:

[DefaultValue(new MyRecord { Value = null })]
public class MyRecord
{
    public MyRecord? Value { get; set; }
}

which would not compile.

from dotnet-avro.

I’d want to give some more thought to Option 2 since that would presumably require generated code to depend on Chr.Avro.Json, but Option 1 definitely seems like a good first step. Codegen is still one big switch statement, but if we refactored a bit to match the schema/serde builder case pattern, that’d give us a mechanism to report warnings.

from dotnet-avro.

Yes I agree. Option 1 seems to me quite valuable even if we take a bit more time fleshing out Option 2.

I don't know whether Option 2 requires any additional dependencies though. Couldn't the default value json be treated as a simple string by the generated code? (and basically ignored until the need to publish a schema arises)

from dotnet-avro.

Yeah, the schema would just be the JSON string, but DefaultSchemaValueJsonAttribute would have to live somewhere.

from dotnet-avro.