Decoding Json data to Avro classes

Question

I have some files records in which are stored as plain text Json. A sample records:

{
      "datasetID": "Orders",
      "recordID": "rid1",
      "recordGroupID":"asdf1",
      "recordType":"asdf1",
      "recordTimestamp": 100,
      "recordPartitionTimestamp": 100,
      "recordData":{
        "customerID": "cid1",
        "marketplaceID": "mid1",
        "quantity": 10,
        "buyingDate": "1481353448",
        "orderID" : "oid1"
      }
}

For each record, recordData may be null. If recordData is present, orderID may be null.

I write the following Avro schema to represent the structure:

[{
  "namespace":"model",
  "name":"OrderRecordData",
  "type":"record",
  "fields":[
    {"name":"marketplaceID","type":"string"},
    {"name":"customerID","type":"string"},
    {"name":"quantity","type":"long"},
    {"name":"buyingDate","type":"string"},
    {"name":"orderID","type":["null", "string"]}
  ]
},
{
  "namespace":"model",
  "name":"Order",
  "type":"record",
  "fields":[
    {"name":"datasetID","type":"string"},
    {"name":"recordID","type":"string"},
    {"name":"recordGroupID","type":"string"},
    {"name":"recordType","type":"string"},
    {"name":"recordTimestamp","type":"long"},
    {"name":"recordPartitionTimestamp","type":"long"},
    {"name":"recordData","type": ["null", "model.OrderRecordData"]}
  ]
}]

Ans finally, I use the following method to de-serialize each String record into my Avro class:

Order jsonDecodeToAvro(String inputString) {
        return new SpecificDatumReader<Order>(Order.class)
           .read(null, DecoderFactory.get().jsonDecoder(Order.SCHEMA$, inputString));
}

But I keep getting the exception when trying to reach the above record:

org.apache.avro.AvroTypeException: Unknown union branch customerID
    at org.apache.avro.io.JsonDecoder.readIndex(JsonDecoder.java:445)

What am I doing wrong? I am using JDK8 and Avro 1.7.7

score 1 · Answer 1 · edited May 23 '17 at 11:45

The json input must be in the form

{
  "datasetID": "Orders",
  "recordID": "rid1",
  "recordGroupID":"asdf1",
  "recordType":"asdf1",
  "recordTimestamp": 100,
  "recordPartitionTimestamp": 100,
  "recordData":{
  "model.OrderRecordData" :{
    "orderID" : null,
    "customerID": "cid1",
    "marketplaceID": "mid1",
    "quantity": 10,
    "buyingDate": "1481353448"
    } 
  }
}

This is because of the way Avro's JSON encoding handles unions and nulls.

Take a look at this:

How to fix Expected start-union. Got VALUE_NUMBER_INT when converting JSON to Avro on the command line?

There is also an open issue regarding this: https://issues.apache.org/jira/browse/AVRO-1582

Decoding Json data to Avro classes

1 Answers1