I found a way to get my record schema so I'm no longer throwing the
same exception. I am now able to put the record indexes for the cloned
record.
GenericRecord castRecord = (GenericRecord) input.getPayloadObject();
final GenericRecord clonedRecord = new GenericData.Record(SCHEMA);
clonedRecord.getSchema().getFields();
int length = SCHEMA.getFields().size();
for (int i = 0; i < length; i++) {
clonedRecord.put(i, castRecord.get(i));
}
GenericDatumWriter<GenericRecord> writer = new
GenericDatumWriter<GenericRecord>(SCHEMA);
ByteArrayOutputStream clonedRecordOutputStream = new ByteArrayOutputStream();
Encoder binaryEncoder =
EncoderFactory.get().binaryEncoder(clonedRecordOutputStream, null);
writer.write(clonedRecord, binaryEncoder);
^^ Throws UnresolvedUnionException ```Caused by:
org.apache.avro.UnresolvedUnionException: Not in union
["null",{"type":"record","name"```
The schema is identical between the records, with the exception of the
name and namespace. Then I don't understand why I'm getting the
exception. I can write with the castRecord and it's schema. Is this a
byte alignment issue caused by the name and namespace? I didn't see
them in the record indexes.
On Sat, Sep 19, 2020 at 3:04 PM Colin Williams
<[email protected]> wrote:
>
> I gave it a shot but from a MapFunction that supposed to be
> serializable. I got an NPE.
>
> I assume I can't create a new Schema.Field from within that
> MapFunction . I didn't seem to have trouble accessing the existing
> schema fields.
>
> > List<Schema.Field> clonedFields = existingFields.stream()
> .map(f -> new Schema.Field(f, f.schema()))
> .collect(Collectors.toList());
>
> On Fri, Sep 18, 2020 at 7:09 PM Colin Williams
> <[email protected]> wrote:
> >
> > Hi Ryan, Thanks for your explanation. I am thinking now that the
> > design of AVRO suggests that data and schemas are very planned things.
> > That changes are planned through versioning and we don't like
> > duplicated schemas (when the positioning makes sense).
> >
> > I have a round about way of learning. Sometimes I am working with data
> > and I think it's convenient to transform my data programmatically and
> > try to obtain a schema from that. Also I think that schemas can become
> > cumbersome when many fields are involved in intricate patterns.
> >
> > I think maybe there are other forms maybe more well suited for that.
> >
> > Regarding your proposals 1,2 seem reasonable to me. But someone like
> > myself might also not fully understand the design of AVRO.
> > A better exception or some kind of lead for armchair programmers to
> > better understand the exception. Thanks for mentioning the copy
> > operation.
> >
> > Finally I do see something about aliases.
> >
> > Thanks,
> >
> > Colin
> >
> >
> >
> > On Fri, Sep 18, 2020 at 5:32 AM Ryan Skraba <[email protected]> wrote:
> > >
> > > Hello Colin, you've hit one bit of fussiness with the Java SDK... you
> > > can't reuse a Schema.Field object in two Records, because a field
> > > knows its own position in the record[1]. If a field were to belong to
> > > two records at different positions, this method would have an
> > > ambiguous response.
> > >
> > > As a workaround, since Avro 1.9, there's a copy constructor that you
> > > can use to clone the field:
> > >
> > > List<Schema.Field> clonedFields = existingFields.stream()
> > > .map(f -> new Schema.Field(f, f.schema()))
> > > .collect(Collectors.toList());
> > >
> > > That being said, I don't see any reason we MUST throw an exception.
> > > There's a couple of alternative strategies we could use in the Java
> > > SDK:
> > >
> > > 1. If the position is the same in both records, allow the field to be
> > > reused (which enables cloning use cases).
> > >
> > > 2. Make a copy of the field to reuse internally if the position is
> > > already set (probably OK, since it's supposed to be immutable).
> > >
> > > 3. Allow the field to be reused, only throw the exception only if
> > > someone calls the position() method later.
> > >
> > > Any of those sound like a useful change for your use case? Don't
> > > hesitate to create a JIRA or contribution if you like!
> > >
> > > All my best, Ryan
> > >
> > > On Fri, Sep 18, 2020 at 8:27 AM Colin Williams
> > > <[email protected]> wrote:
> > > >
> > > > Hello,
> > > >
> > > > I'm trying to understand working with Avro records and schemas,
> > > > programmatically. Then I was first trying to create a new schema and
> > > > records based on existing records, but with a different name /
> > > > namespace. It seems then I don't understand getFields() or
> > > > createRecord(...). Why can't I use the fields obtained from
> > > > getFields() in createRecord()? How would I go about this properly?
> > > >
> > > > // for an existing record already present
> > > > GenericRecord someRecord
> > > >
> > > > // get a list of existing fields
> > > > List<Schema.Field> existingFields = someRecord.getSchema().getFields();
> > > >
> > > > // schema for new record with existing fields
> > > > Schema updatedSchema = createRecord("UpdatedName",
> > > > "","avro.com.example.namespace" , false, existingFields);
> > > >
> > > > ^^ throws an exception ^^
> > > >
> > > > /* Caused by: org.apache.avro.AvroRuntimeException: Field already
> > > > used: eventMetadata type:UNION pos:0
> > > > at org.apache.avro.Schema$RecordSchema.setFields(Schema.java:888)
> > > > at org.apache.avro.Schema$RecordSchema.<init>(Schema.java:856)
> > > > at org.apache.avro.Schema.createRecord(Schema.java:217)
> > > > */
> > > >
> > > > final int length = fields.size();
> > > >
> > > > GenericRecord clonedRecord = new GenericData.Record(updatedSchema);
> > > > for (int i = 0; i < length; i++) {
> > > > final Schema.Field field = existingFields.get(i);
> > > > clonedRecord.put(i, someRecord.get(i));
> > > > }
> > > >
> > > >
> > > > Best Regards,
> > > >
> > > > Colin Williams
