Write avro file to a memory stream, then read it out again, using reflection.

WriteAndReadAvroFileUsingReflection.cs

// Write avro file to a memory stream, then read it out again, using reflection.
// Based on the very sparse C# docs from https://avro.apache.org/docs/1.11.1/api/csharp/html/md_src_apache_main_Reflect_README.html
// combined with the Java docs from https://avro.apache.org/docs/1.11.1/getting-started-java/

var baseClassSchema = @"
    [
        { ""type"" : ""record"", ""name"" : ""Derived1"", ""fields"" :
            [
                { ""name"" : ""A"", ""type"" : ""string""},
                { ""name"" : ""B"", ""type"" : ""int""}
            ]
        },
        { ""type"" : ""record"", ""name"" : ""Derived2"", ""fields"" :
            [
                { ""name"" : ""A"", ""type"" : ""string""},
                { ""name"" : ""C"", ""type"" : ""double""}
            ]
        },
 
    ]
    ";

var schema = Schema.Parse(baseClassSchema);
var derived1write = new Derived1() { A = "derived1", B = 7 };
var derived2write = new Derived2() { A = "derived2", C = 3.14 };

// union types (except for [null, type]) need to be manually registered
var unionSchema = schema as UnionSchema;
var cache = new ClassCache();
cache.LoadClassCache(typeof(Derived1), unionSchema[0]);
cache.LoadClassCache(typeof(Derived2), unionSchema[1]);
var x = schema as RecordSchema;

var writer = new ReflectWriter<BaseClass>(schema, cache);

using (var stream = new MemoryStream(256))
{
    using (var fileWriter = DataFileWriter<BaseClass>.OpenWriter(writer, stream, leaveOpen: true))
    {
        fileWriter.Append(derived1write);
        fileWriter.Append(derived2write);
        fileWriter.Flush();
    }
    
    stream.Position = 0;
    foreach(var item in ReadAvroFileStreamUsingReflection<BaseClass>(stream))
    {
        Console.WriteLine(item);
    }
}

IEnumerable<T> ReadAvroFileStreamUsingReflection<T>(Stream stream)
{
    using (var fileReader = DataFileReader<T>.OpenReader(stream, null, (writerSchema, readerSchema) => new ReflectReader<T>(writerSchema, readerSchema, cache)))
    {
        while (fileReader.HasNext())
        {
            var nextItem = fileReader.Next();
            yield return nextItem;
        }
    }
}


public class BaseClass
{
    public string A { get; set; }
}

public class Derived1 : BaseClass
{
    public int B { get; set; }
}

public class Derived2 : BaseClass
{
    public double C { get; set; }
}