[AVRO-1490] GenericDatumWriter throws exception for nullable schema fields

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Cannot Reproduce
• Affects Version/s: 1.7.6
• Component/s: csharp

Environment

Windows, C#, .Net 4.5

• Assignee: Unassigned
• Reporter: Johan Sundstrom
• Created: 31/Mar/14 18:29
• Updated: 17/Mar/22 14:23
• Resolved: 17/Mar/22 14:23

Description

providing sample code and fix

Sample Schema:

{"namespace": "AvroSample",
 "type": "record",
 "name": "User",
 "fields": [
     {"name": "name", "type": "string"},
     {"name": "favorite_number",  "type": ["int", "null"]},
     {"name": "favorite_color", "type": ["string", "null"]}
 ]
}

Sample code to recreate

namespace AvroSample
{
    class Program
    {
        static void Main(string[] args)
        {
            Schema schema = LoadSchemaFromFile(@"user.avpr");

            GenericRecord user1 = new GenericRecord((RecordSchema)schema);
            user1.Add("name", "Alyssa");
            user1.Add("favorite_number", 256);
            // Leave favorite color null

            GenericRecord user2 = new GenericRecord((RecordSchema)schema);
            user2.Add("name", "Ben");
            user2.Add("favorite_number", 7);
            user2.Add("favorite_color", "red");

            // Serialize user1 and user2 to disk
            String outPath = @"C:\\users.avro";

            GenericDatumWriter<GenericRecord> datumWriter = new GenericDatumWriter<GenericRecord>(schema);
            IFileWriter<GenericRecord> dataFileWriter = DataFileWriter<GenericRecord>.OpenWriter(datumWriter, outPath);

            dataFileWriter.Append(user1);
            dataFileWriter.Append(user2);
            dataFileWriter.Dispose();

            // Deserialize users from disk
            
            IFileReader<User> dataFileReader = DataFileReader<User>.OpenReader(outPath);//, schema);
            User user = null;
            while (dataFileReader.HasNext())
            {
                // Reuse user object by passing it to next(). This saves us from
                // allocating and garbage collecting many objects for files with
                // many items.
                user = dataFileReader.Next();
                Console.WriteLine("Name={0}", user.name);  
                Console.WriteLine(user.ToString());
            }

            Console.WriteLine("Press any key to continue...");
            Console.ReadKey();
        }

        static Schema LoadSchema(string json)
        {
            Schema schema = Schema.Parse(json);
            return schema;
        }

        static Schema LoadSchemaFromFile(string filePath)
        {
            String json = File.ReadAllText(filePath, Encoding.UTF8);
            return LoadSchema(json);
        }
    }
}

Code that fixes issue:

protected override void WriteRecordFields(object recordObj, RecordFieldWriter[] writers, Encoder encoder)
        {
            var record = (GenericRecord) recordObj;
            foreach (var writer in writers)
            {
                  // Change from 
                  // writer.WriteField(record[writer.Field.Name], encoder);
                  // to
                object result = null;
                record.TryGetValue(writer.Field.Name, out result);
                writer.WriteField(result, encoder);
            }
        }
}