Kafka Producer Error: ' Value serializer not specified and there is no default serializer defined for type ...'

Question

I just started using Kafka and hit the following rookie error:

'Value cannot be null.
Parameter name: Value serializer not specified and there is no default serializer defined for type ActMessage.'

It happens when trying to send a class object, ActMessage object, rather then the a simple string that comes with the example. The line of code that raises the erros is:

using (var p = new ProducerBuilder<Null, ActMessage>(config ).Build()

I am using the .net client.

My understanding is that i need to use one of the default serializes in the first type parameter, one that come with Kafka client, as explained here, but can't find them on this .net package. I guess i could build one but that would be a waste of time.

Here a reproducible example:

public class ActMessage  {
    public int SomeId {get;set;}
    public string SomeContent {get;set;}
}

class Tester  {

void send(){

    var config = new ProducerConfig { BootstrapServers = "localhost:9092" };

        using (var p = new ProducerBuilder<Null, ActMessage>(config).Build()) //throws error here
        {
            var dr = p.ProduceAsync("news", new Message<Null, ActMessage>
            {
                Value = new ActMessage { SomeId = 1, SomeContent="hi" },
            }
                ).Result;
        }
    }
}

Answer 1

I suggest checking out the working examples/ dir in that repo to see working code that you can copy into your own projects.

---

If you have your own class, you need to implement the ISerializer and IDeserializer interfaces.

Or you can use the built-in ones

---

However, an alternative is to use Avro

This requires writing an Avro schema file, then using avrogen to create your class, not manually write it. E.g.

dotnet tool install --global Apache.Avro.Tools

avrogen -s User.avsc .

Then you must always add some ValueSerializer in Kafka clients in order to send data