[
https://issues.apache.org/jira/browse/AVRO-3520?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17539481#comment-17539481
]
Christophe Le Saec commented on AVRO-3520:
------------------------------------------
For the existing encoded binaries (that are already exits), as it does not
embed schema information, i suggest the reader try to get information for added
field :
{code:java}
@Override
protected MyCustomv2 read(Object object, Decoder in) {
// ... fill in field of first version
// For fields in new version, potentially non exists
try {
mc.setNewField(in.readString());
}
catch (IOException ex) {}
}
{code}
(This imply that new fields are added at end of Record, and support no other
kind of change)
For futur encoded binaries, you could put schema information on record itself,
{code:java}
final Field version = new Field("version", Schema.create(Schema.Type.INT),
"schelma version", 0);
...
Schema.createRecord("record", "doc", "namespace", false, Arrays.asList(version,
...));
{code}
Then, use this "metadata" field to store object version
For instance, with second version
{code:java}
@Override
protected void write(Object datum, Encoder out) throws IOException {
...
out.writeInt(2); // version 2
...
}
@Override
protected MyCustom_versionX read(Object reuse, Decoder in) throws
IOException {
....
int version = in.readInt();
// So, you can have an adapted code to the version
}
@Override
protected Schema getSchema() {
// return version 2
}
{code}
(This allow more modification than simply add field, but also, change field
type (from int to float for example ...))
Hope it will help.
> CustomEncoding doesn't expose the read schema
> ---------------------------------------------
>
> Key: AVRO-3520
> URL: https://issues.apache.org/jira/browse/AVRO-3520
> Project: Apache Avro
> Issue Type: Bug
> Components: java
> Affects Versions: 1.11.0
> Reporter: Colin
> Priority: Major
>
> Currently it is not possible to detect a schema change when using
> `CustomEncoding<T>`.
--
This message was sent by Atlassian Jira
(v8.20.7#820007)
