Kotlinx.serialization: Convert Int to Boolean with custom serializer

[xdma]

Hi, I've already spent a lot of time trying to write custom serializer, to replace Int (TINYINT from mysql) to Boolean.

Using Gson I do it without problems, something like this (java):
` public class BooleanSerializer implements JsonSerializer, JsonDeserializer {

    @Override
    public JsonElement serialize(Boolean arg0, Type arg1, JsonSerializationContext arg2) {
        return new JsonPrimitive(arg0 ? 1 : 0);
    }

    @Override
    public Boolean deserialize(JsonElement arg0, Type arg1, JsonDeserializationContext arg2) throws JsonParseException {
        return arg0.getAsInt() == 1;
    }
}

GsonBuilder().registerTypeAdapter(Boolean.class, serializer)
`

Is it possible to achieve the same result here and how?
Thank you.

[Skeptick]

As I understand it, this is not possible at the moment. I use for this:

@Serializable
data class BooleanInt(val value: Boolean) {

    @Serializer(forClass = BooleanInt::class)
    companion object : KSerializer<BooleanInt> {
        override fun save(output: KOutput, obj: BooleanInt) =
            output.writeIntValue(if (obj.value) 1 else 0)

        override fun load(input: KInput): BooleanInt =
            BooleanInt(input.readNullable(IntSerializer) == 1)
    }
}

And:

@Serializable
data class Example(
    @SerialName("my_bool") val myBool: BooleanInt
)

[xdma]

Yes, I did the same, but it's not very convenient

[sandwwraith]

Or you can use @Serializable(with=...) on boolean properties which you need to convert with custom serializer.

Currently, indeed, there is no option to override default serializers globally.

[pdvrieze]

Given the way the serialization code is generated by the plugin overriding the only straightforward way is to have a delegating writer and reader where the boolean option is redirected.

[qwwdfsad]

@xdma
Even though globally one can't override Boolean serializer, it's possible to achieve locally.
For your custom serialization format, it's possible to write custom KInput/KOutput, which can hook into writeBooleanValue and readBooleanValue.

If you need such feature in JSON (do you?), we can provide different implementation/builder which allows to hookup into specific serialization points by target ::class or KSerialClassDesc

[xdma]

@qwwdfsad

Thanks, I already solved the problem, as @Skeptick advised, it's less convenient, but it works and I don't want to go back to that part of project now :)

[sandwwraith]

You can now also use @file:UseSerializers to override default serializers on a per-file basis.