>From the spec:
> A union is encoded by first writing an int value indicating the
zero-based position within the union of the schema of its value. The value
is then encoded per the indicated schema within the union.
In other words 'value' doesn't have a way for the decoder to figure out
which type is in the union.
(Where are you getting this example from?)
J
On Fri, May 21, 2021 at 12:36 AM svend frolund <svendf2...@gmail.com> wrote:
> Hello,
>
> I cannot seem to get avro union types to work properly in the c++ codebase
> that I pulled from your github repo a couple of weeks ago. I want to
> specify that an object attribute can be either null or a string in order to
> capture some notion of optional attributes in my json data. However, when
> decoding data that actually has a string value for the "optional" attribute
> in question, I get the following exception: "Incorrect token in the stream.
> Expected: Object start, found String". Here is a small program that
> replicates the issue:
>
> std::string schema;
> schema += "{";
> schema += " \"name\" : \"simple\", ";
> schema += " \"type\" : \"record\", ";
> schema += " \"fields\" : [ { \"name\" : \"last\", \"type\" : [
> \"null\", \"string\"] } ] ";
> schema += "}";
>
> std::string value;
> value += "{";
> value += " \"last\" : \"dog\" ";
> value += "}";
>
> std::istringstream schemass(schema);
> std::istringstream valuess(value);
>
> avro::ValidSchema cpxSchema;
> avro::compileJsonSchema(schemass, cpxSchema);
>
> std::unique_ptr<avro::InputStream> json_is =
> avro::istreamInputStream(valuess);
>
> /* JSON decoder */
> avro::DecoderPtr json_decoder = avro::jsonDecoder(cpxSchema);
> avro::GenericDatum *datum = new avro::GenericDatum(cpxSchema);
>
> try
> {
> /* Decode JSON to Avro datum */
> json_decoder->init(*json_is);
> avro::decode(*json_decoder, *datum);
> }
> catch(const avro::Exception &_e)
> {
> // throws Incorrect token in the stream. Expected: Object start,
> found String
> }
>
> Do I need to configure the system in a particular way for this to work, or
> does the current implementation simply not support these types of unions.
>
> I sincerely hope someone can help!
>
> All the best,
>
> Svend
>
