PropertyNamingStrategy doesn't work during deserialization

simple kotlin snippet to reproduce:

class JacksonTest {

    @Test
    fun testSnakeCaseDeserialization() {
        val json = """{"my_camel_case":10001}"""
        val objectMapper = jacksonObjectMapper().findAndRegisterModules()
        val obj = objectMapper.readValue<TestSnakeCase>(json)
        println(obj)
        assertEquals(10001, obj.myCamelCase)
    }

    @Test
    fun testSnakeCaseSerialization() {
        val objectMapper = jacksonObjectMapper().findAndRegisterModules()
        val obj = TestSnakeCase(10001)
        println(objectMapper.writeValueAsString(obj))
    }

    @JsonNaming(PropertyNamingStrategy.SnakeCaseStrategy::class)
    data class TestSnakeCase(val myCamelCase: Int)
}

also happens in Java

[unlimitedsola]

Oops, This is interesting, I didn’t notice it only happens on POJO that has exactly one property. add @JsonCreator(mode = JsonCreator.Mode.PROPERTIES) and everything works fine. Thanks!

[cowtowncoder]

@unlimitedsola Yes this is… sort of unfortunate thing, and commonly stumbled upon. So there are two interpretations here: with just 1 property, one could either consider mapping exact value (“delegating”), or JSON Object of just one property (“property-based”). Jackson tries to use heuristics if not explicitly specified but I don’t think there is anything that can ultimately tell it, short of allowing configuration for defaulting (mode used if not annotated) and allowing overrides.

mode property was added to allow explicit annotation: if you had added explicit name annotation with @JsonProperty this would also have happened. It is only ambiguous if name is derived from bytecode.