Hello John, Thanks for your reply! The example is home-brewed. I tried to construct a "minimal" example that illustrates my problem. As far as I understand the situation, the json object that I refer to as "value" ought to comply with the avro schema in "schema". Another value object were the "last" attribute is null should also comply with the schema. I thought the decoder would parse the "value" object against the schema, and determine that the actual type for the attribute "last" is indeed a string (as opposed to null), and decode the union as prescribed by the specification, by encoding a value of 1 (the position of "string" in the union) along with the actual string value. But are you telling me that it is expected behavior when the decoder is unable to decode the "value" object according to "schema"?
--Svend On Fri, May 21, 2021 at 5:02 PM John McClean <[email protected]> wrote: > 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 <[email protected]> > 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 >> >
