Generic classes lead to serialisation issues

[upMKuhn]

Hello,

I have a class called DatedValue of type String and Double. The schema for this class is generated wrongly. As you can see the first definition says the value is of type string and then this reference is wrongly repeated. Is this a bug in avro4k or a limitation in avro schemas?

Thank you!

java.lang.ClassCastException: value 638.2585562648774 (a java.lang.Double) cannot be cast to expected type string at [v1, v1, v1, v1, v1, v1, v1, v1][v1].owners[0].quantity[0].value at org.apache.avro.path.TracingClassCastException.summarize(TracingClassCastException.java:79) at org.apache.avro.path.TracingClassCastException.summarize(TracingClassCastException.java:30) at org.apache.avro.generic.GenericDatumWriter.write(GenericDatumWriter.java:84) at com.github.avrokotlin.avro4k.io.DefaultAvroOutputStream.write(DefaultAvroOutputStream.kt:32) at com.github.avrokotlin.avro4k.io.AvroOutputStream$DefaultImpls.write(AvroOutputStream.kt:22) at com.github.avrokotlin.avro4k.io.DefaultAvroOutputStream.write(DefaultAvroOutputStream.kt:15)

@Serializable
data class Owner(
    val brokerId: String,
    val type: Int,
    val name: List<DatedValue<String>>,
    val quantity: List<DatedValue<Double>>
) {
    companion object
}

@Serializable
data class DatedValue<T>(
    @Serializable(with = LocalDateSerializer::class)
    val asOfDate: LocalDate,
    val value: T
) {
    companion object
}

Schema

        {
          "name": "owners",
          "type":
            {
              "type": "array",
              "items":
                {
                  "type": "record",
                  "name": "Owner",
                  "namespace": "com.mk.trading.broker.models.contracts.fundamentals",
                  "fields":
                    [
                      { "name": "brokerId", "type": "string" },
                      { "name": "type", "type": "int" },
                      {
                        "name": "name",
                        "type":
                          {
                            "type": "array",
                            "items":
                              {
                                "type": "record",
                                "name": "DatedValue",
                                "fields":
                                  [
                                    { "name": "asOfDate", "type": "string" },
                                    { "name": "value", "type": "string" },
                                  ],
                              },
                          },
                      },
                      {
                        "name": "quantity",
                        "type": { "type": "array", "items": "DatedValue" },
                      },
                    ],
                },
            },
        },

[thake]

Hey @upMKuhn, this seems to be a bug in avro4k. Thanks for bringing it up. Can you provide a branch with a Junit-Testcase? This helps a lot to track down the cause.

[upMKuhn]

Done, I added a schema test :)

fyi: @thake

https://github.com/avro-kotlin/avro4k/pull/154

[thake]

Thanks, I will have a look into it!

[thake]

Hey @upMKuhn, I've dug a little bit deeper and found an Avro-Issue that states that Avro, as of now, does not support parameterized types. Until this issue is resolved, I wouldn't know how to correctly generate a schema for a parameterized type.

As a workaround, you could do the following:

```kotlin
@Serializable
data class Owner(
  val brokerId: String,
  val type: Int,
  val name: List<StringDatedValue>,
  val quantity: List<DoubleDatedValue>
)
interface DatedValue<T> {  
  val asOfDate: LocalDate
  val value:  T
}
@Serializable
data class StringDatedValue(
  @Serializable(with = LocalDateSerializer::class)
  override val asOfDate: LocalDate,
  override val value: String
) : DatedValue<String>

@Serializable
data class DoubleDatedValue(
  @Serializable(with = LocalDateSerializer::class)
  override val asOfDate: LocalDate,
  override val value: Double
) : DatedValue<Double>

[upMKuhn]

Nice thank you!

[Chuckame]

But in parallel, kotlinx serialization should handle nested generics, another feature to take into account in #148

[thake]

Closing this issue for now. If parameterized types are supported in avro, we'll open a new issue.