We're mid-migration from Moshi to kotlinx.serializ...

# serialization

[Rafał Borcz]

We're mid-migration from Moshi to kotlinx.serialization. Our shared Json uses explicitNulls = false (omit nulls, matching Moshi defaults), which fits almost every model. But a few models need the opposite, they must emit explicit `null`s on encode.

The catch is that explicitNulls = false always drops nulls, before any per-field @Serializable(with=…) or @EncodeDefault can run.

Two options we've found, both with downsides:
1. A second Json (explicitNulls = true) + marker annotation + Retrofit converter routing those models to it. Clean at the model, but adds a whole extra Json + qualifier + dual-delegate routing infra.
2. A custom KSerializer that builds the JSON tree by hand and writes JsonNull. Single Json, transparent through Retrofit but it can't wrap the generated serializer, so it's fully hand-written field-by-field. Lots of boilerplate.
Has anyone hit this and found a third option to flip explicitNulls per field or class? It'd be handy if kotlinx had an @EncodeExplicitNull annotation, similar to the existing @EncodeDefault .

[ephemient]

consider filing a feature request upstream, similar to @EncodeDefault which takes precedence over Json { encodeDefaults }

[ephemient]

but I think you don't actually need to create a complete new serializer, e.g. https://pl.kotl.in/Pc9H0dgH5 should just be a few lines of boilerplate per affected serializable class

[Rafał Borcz]

@ephemient
Wow, I had no idea about @KeepGeneratedSerializer and generatedSerializer(). That's a huge help with my boilerplate problem. I tried it out and it works really well in my case. Thanks a lot for the help. I was starting to lose my mind trying to figure out a better way to do this 😄