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https://issues.apache.org/jira/browse/AVRO-1905?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Sean Busbey resolved AVRO-1905.
-------------------------------
Resolution: Information Provided
Assignee: Sean Busbey
When using Apache Avro as a serialization format, you must always know what
schema was used to write the data and present that schema to the library as a
part of reading.
In your examples above, it appears you are attempting to read data written with
_old_schema_ using only _new_schema_, which will not work. Avro will need to
know both _old_schemea_ and _new_schema_.
Please use the user@avro mailing list for help with getting started using Avro:
http://avro.apache.org/mailing_lists.html#Users. It is easiest to do so by
first subscribing to the user list and then posting your question.
> Backward and forward compatible
> -------------------------------
>
> Key: AVRO-1905
> URL: https://issues.apache.org/jira/browse/AVRO-1905
> Project: Avro
> Issue Type: Bug
> Components: java
> Reporter: Amod Kumar Pandey
> Assignee: Sean Busbey
>
> I am under the understanding that Avro is both backward and forward
> compatible (for certain schema changes). But as per my test it is neither
> backward nor forward compatible.
> Maven project with avro
> {code}
> {"namespace": "example.avro",
> "type": "record",
> "name": "user",
> "fields": [
> {"name": "name", "type": "string"},
> {"name": "favorite_number", "type": "int"}
> ]
> }
> {code}
> Producer
> {code}
> public class Producer {
> public static void main(String[] args) throws IOException {
> try (ByteArrayOutputStream outputStream = new ByteArrayOutputStream()) {
> user u1 =
> user.newBuilder().setFavoriteNumber(1).setName("Amod").build();
> writeBinaryEncodedAvro(u1, outputStream);
> user u2 =
> user.newBuilder().setFavoriteNumber(2).setName("Pandey").build();
> writeBinaryEncodedAvro(u2, outputStream);
> System.out.println(Arrays.toString(outputStream.toByteArray()));
> }
> }
> static void writeBinaryEncodedAvro(SpecificRecord specificRecord,
> OutputStream os) throws IOException {
> BinaryEncoder binaryEncoder = EncoderFactory.get().binaryEncoder(os,
> null);
> @SuppressWarnings("unchecked")
> DatumWriter<SpecificRecord> datumWriter =
> new SpecificDatumWriter<SpecificRecord>((Class<SpecificRecord>)
> specificRecord.getClass());
> datumWriter.write(specificRecord, binaryEncoder);
> binaryEncoder.flush();
> }
> }
> {code}
> Consumer
> {code}
> public class Consumer {
> public static void main(String[] args) throws IOException {
> byte[] data = {8, 65, 109, 111, 100, 2, 10, 103, 114, 101, 101, 110};
> try (ByteArrayInputStream inputStream = new ByteArrayInputStream(data)) {
> System.out.println(fromBinaryMulti(inputStream));
> }
> }
> static user fromBinary(InputStream is) throws IOException {
> BinaryDecoder binaryDecoder = DecoderFactory.get().binaryDecoder(is,
> null);
> DatumReader<user> datumReader = new SpecificDatumReader<user>(user.class);
> return datumReader.read(null, binaryDecoder);
> }
> static List<user> fromBinaryMulti(InputStream is) throws IOException {
> List<user> users = new ArrayList<user>();
> BinaryDecoder binaryDecoder = DecoderFactory.get().binaryDecoder(is,
> null);
> while (!binaryDecoder.isEnd()) {
> DatumReader<user> datumReader = new
> SpecificDatumReader<user>(user.class);
> users.add(datumReader.read(null, binaryDecoder));
> }
> return users;
> }
> }
> {code}
> I changed the schema to
> {code}
> {"namespace": "example.avro",
> "type": "record",
> "name": "user",
> "fields": [
> {"name": "name", "type": "string"},
> {"name": "favorite_number", "type": "int"},
> {"name": "favorite_color", "type": "string", "default": "green"}
> ]
> }
> {code}
> The following does not work.
> Consume code using new schema generated code cannot consume byte array
> generated by old schema.
> Consume code using old schema generated code cannot consume byte array
> generated with new schema.
> Is there a problem in the way I am trying to understand the forward or
> backward compatibility.
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