Example for schema evolution?

Hi there,

Looking at the docs, you reference “Compatibility and schema evolution”, but I am unable to find any example on how to achieve schema evolution, which is one of the main benefits of using Avro.

For example: I would like new consumers to be able to read old producer data. Does this library support this?

For example:

V1 schema

{
    "type": "record",
    "name": "Foo",
    "fields": [
        {
            "name": "f1",
            "type": "string"
        }
    ]
}

V2 schema

{
    "type": "record",
    "name": "Foo",
    "fields": [
        {
            "name": "f1",
            "type": "string"
        },
        {
            "name": "f2",
            "type": "string",
            "default": "",
        }
    ]
}

I would like V2 consumers to have the property f2 with value "" when reading data produced with schema v1, but this does not happen, since the message is decoded using the old schema

[nick-zh]

I just saw, there is already an open PR for this #137

[ivank]

At our shop we had developed a simpler implementation of schema registry back in the day, since this project was not yet available. Its called Castle (as in "Kafka’s greatest work 😃).

Anyway we’ve recently encountered this issue ourselves, so we did implement reader schemas.

You guys are right, Avsc does support it with createResolver, and it’s pretty easy to implement. I’d be happy to give it a go and try to write a PR for it here too, if I had some guidance where you’d think its best to add it.