Encode GenericData.Record field separately as encoded key

I am trying to use Avro to encode key / value pairs, but can't figure out how to encode just a single field in a schema / GenericData.Record in order to make the key.

Take this simple schema:

{"name":"TestRecord", "type":"record", "fields":[
  {"name":"id", "type":"long"},
  {"name":"name", "type":"string"},
  {"name":"desc", "default":null, "type":["null","string"]}
]}

I am encoding records like this:

val testRecordSchema = schemaParser.parse(testRecordSchemaString)
val writer = new GenericDatumWriter[GenericRecord](testRecordSchema)
val baos = new ByteArrayOutputStream()
val encoder = EncoderFactory.get().binaryEncoder(baos, null)
val record = new org.apache.avro.generic.GenericData.Record(schema)
record.put("id", 1L)
record.put("name", "test")
writer.write(record, encoder)
encoder.flush

But now say I wanted to encode separately just the id field, to use as the key, and I want to do it by name because sometimes I want to use the name field as the key instead of the id.

I tried multiple permutations of GenericDatumWriter. GenericDatumWriter has a method called writeField that looks promising, but it is protected. Otherwise it looks like you have to write complete records.

I could wrap my field in a new record type defined in a new schema, for example:

{"name":"TestRecordKey", "type":"record", "fields":[
  {"name":"id", "type":"long"}
]}

I'm 100% sure I can make that work, but then I have to create a new record type and manage it for every key field. That's not minor, and it really seems like there should be some more simple way to do this.

Solution

As it turns out, it wasn't that difficult just to create a new record-type schema with only one field -- the field I want to use as the key, like the example I have above:

{"name":"TestRecordKey", "type":"record", "fields":[
  {"name":"id", "type":"long"}
]}

I do it on the fly, as I initialize my Schema.Parser with the payload schemas -- I just create the key schema based on the payload schema programmatically.

Was hoping for a less long-hand solution, but this works. I'll still upvote and accept any solution that is cleaner.