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Avro, mail # user - Schema resolution failure when the writer's schema is a primitive type and the reader's schema is a union


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Re: Schema resolution failure when the writer's schema is a primitive type and the reader's schema is a union
Scott Carey 2012-08-31, 16:23
Yes, please file a bug in JIRA.  It will get more attention there.

On 8/30/12 11:06 PM, "Alexandre Normand" <[EMAIL PROTECTED]>
wrote:

> That's one of the things I've tried already. I've reversed the order to
> ["int", "null"] but I get the same result.
>
> Should I file a bug in Jira?
>
> --
> Alex
>
>
> On Thursday, August 30, 2012 at 11:01 PM, Scott Carey wrote:
>>
>> My understanding of the spec is that promotion to a union should work as
>> long as the prior type is a member of the union.
>>
>> What happens if the union in the reader schema union order is reversed?
>>
>> This may be a bug.
>>
>> -Scott
>>
>> On 8/16/12 5:59 PM, "Alexandre Normand" <[EMAIL PROTECTED]>
>> wrote:
>>
>>
>>> Hey,
>>> I've been running into this case where I have a field of type int but I
>>> need to allow for null values. To do this, I now have a new schema that
>>> defines that field as a union of
>>> null and int such as:
>>> type: [ "null", "int" ]
>>> According to my interpretation of the spec, avro should resolve this
>>> correctly. For reference, this reads like this (from
>>> http://avro.apache.org/docs/current/spec.html#Schema+Resolution):
>>>
>>> if
>>> reader's is a union, but writer's is not
>>> The first schema in the reader's union that matches the writer's schema
>>> is recursively resolved against it. If none match, an error is signaled.)
>>>
>>>
>>> However, when trying to do this, I get this:
>>> org.apache.avro.AvroTypeException: Attempt to process a int when a union
>>> was expected.
>>>
>>> I've written a simple test that illustrates what I'm saying:
>>> @Test
>>> public void testReadingUnionFromValueWrittenAsPrimitive() throws
>>> Exception {
>>> Schema writerSchema = new Schema.Parser().parse("{\n" +
>>> " \"type\":\"record\",\n" +
>>> " \"name\":\"NeighborComparisons\",\n" +
>>> " \"fields\": [\n" +
>>> " {\"name\": \"test\",\n" +
>>> " \"type\": \"int\" }]} ");
>>> Schema readersSchema = new Schema.Parser().parse(" {\n" +
>>> " \"type\":\"record\",\n" +
>>> " \"name\":\"NeighborComparisons\",\n" +
>>> " \"fields\": [ {\n" +
>>> " \"name\": \"test\",\n" +
>>> " \"type\": [\"null\", \"int\"],\n" +
>>> " \"default\": null } ] }");
>>> GenericData.Record record = new GenericData.Record(writerSchema);
>>> record.put("test", Integer.valueOf(10));
>>>
>>> ByteArrayOutputStream output = new ByteArrayOutputStream();
>>> JsonEncoder jsonEncoder >>> EncoderFactory.get().jsonEncoder(writerSchema, output);
>>> GenericDatumWriter<GenericData.Record> writer = new
>>> GenericDatumWriter<GenericData.Record>(writerSchema);
>>> writer.write(record, jsonEncoder);
>>> jsonEncoder.flush();
>>> output.flush();
>>>
>>> System.out.println(output.toString());
>>>
>>> JsonDecoder jsonDecoder >>> DecoderFactory.get().jsonDecoder(readersSchema, output.toString());
>>> GenericDatumReader<GenericData.Record> reader >>> new GenericDatumReader<GenericData.Record>(writerSchema,
>>> readersSchema);
>>> GenericData.Record read = reader.read(null, jsonDecoder);
>>> assertEquals(10, read.get("test"));
>>> }
>>>
>>> Am I misunderstanding how avro should handle such a case of schema
>>> resolution or is the problem in the implementation?
>>>
>>> Cheers!
>>>
>>> --
>>> Alex
>