I have to deserialize JSON, where a field can be a...

# serialization

[Lukasz Kalnik]

I have to deserialize JSON, where a field can be any JSON primitive (e.g. null, int, string, double, boolean). Can I just define it in my data model as JsonPrimitive and it will work out-of-the-box?

@Serializable
data class Response(
    val field: JsonPrimitive
)

[Lukasz Kalnik]

Responses can be:

{ "field":134 }
{ "field":false }
{ "field":null }

[Lukasz Kalnik]

Although JsonPrimitive always contains a String, so it doesn't seem to work.

[Lukasz Kalnik]

So I probably need to write a custom serializer for this?

[hellman]

I have such a case and use JsonPrimitive. Works fine. See https://kotlinlang.org/api/kotlinx.serialization/kotlinx-serialization-json/kotlinx.serialization.json/-json-primitive/

[Lukasz Kalnik]

Thanks! Can I somehow check the subtype of the parsed JsonPrimitive?

[Lukasz Kalnik]

If it contains an Int, String etc.

[hellman]

Basically I do

if (jsonPrimitive.contentOrNull == null) {
    // It's null
} else if (jsonPrimitive.booleanOrNull != null) {
    // Boolean
} else if (jsonPrimitive.doubleOrNull != null) {
    // It's a Double
} ...

[Lukasz Kalnik]

ok, that should work as well

[Lukasz Kalnik]

Thanks!

[hellman]

Check MEmbers & Extensions in the docs link.

[Lukasz Kalnik]

Yes, I see there are all extensions which I need

[hellman]

I don't get why the extensions are hidden as default 🙂

[trevjones]

don't forget to shame whoever designed that api enough that they never do it again

[Lukasz Kalnik]

😄

[Lukasz Kalnik]

It's an open source project 😉 Flagsmith

[hellman]

I've seen this enough times to accept that it is some sort of pattern used by some developers.

While cumbersome to work with, you do get to say that your app can handle polymorphic data. 🙂

[trevjones]

I think the pattern is more a byproduct of javascript/node letting people play fast and loose with typing. at least that is what my gut tells me

[trevjones]

and/or python

[hellman]

Maybe. But then I did see this back in the days when we used XML instead. 🙂

<field>12345</field>
<field>some string</field>
<field>true</field>

Handling boolean in those cases was interesting...