EXTERNAL_PROPERTY doesn't work with @JsonIgnoreProperties

[ashlanderr]

I am using polymorphic deserialization with Kotlin data classes like this:

@JsonIgnoreProperties(ignoreUnknown = true)
data class Value(
    val type: String,

    @JsonTypeInfo(
        use = JsonTypeInfo.Id.NAME,
        include = JsonTypeInfo.As.EXTERNAL_PROPERTY,
        property = "type",
        defaultImpl = Default::class
    )
    val data: Default
)

object Default

trying to deserialize:

val data = """[{"type": "test","data": {},"additional": {}}]"""

val mapper = ObjectMapper()
    .registerModule(KotlinModule())

val result = mapper.readValue<List<Value>>(data)

and I get this error:

Exception in thread "main" com.fasterxml.jackson.module.kotlin.MissingKotlinParameterException: Instantiation of [simple type, class app.Value] value failed for JSON property type due to missing (therefore NULL) value for creator parameter type which is a non-nullable type
 at [Source: (String)"[{"type": "test","data": {},"additional": {}}]"; line: 1, column: 45] (through reference chain: java.util.ArrayList[1]->app.Value["type"])
	at com.fasterxml.jackson.module.kotlin.KotlinValueInstantiator.createFromObjectWith(KotlinValueInstantiator.kt:112)
	at com.fasterxml.jackson.databind.deser.impl.PropertyBasedCreator.build(PropertyBasedCreator.java:198)
	at com.fasterxml.jackson.databind.deser.impl.ExternalTypeHandler.complete(ExternalTypeHandler.java:316)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeUsingPropertyBasedWithExternalTypeId(BeanDeserializer.java:1001)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeWithExternalTypeId(BeanDeserializer.java:853)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:324)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeOther(BeanDeserializer.java:194)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:161)
	at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:286)
	at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:245)
	at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:27)
	at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4202)
	at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3205)
	at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3188)
	at app.ApplicationKt.main(Application.kt:52)

If I will remove "additional" property from serialized JSON, add "additional" property to the Value class, or remove polymorphic deserialization, then the error will go away. I am using @JsonIgnoreProperties(ignoreUnknown = true) annotation, so I expected that the original case would work.

Jackson Version: 2.10.2

[cowtowncoder]

I think this is Kotlin-specific, as data classes handling of creators, null checks, is quite customized.
Will transfer.

May be transferred back if Java-only reproduction exists (if so let me know and I can move it).

[ashlanderr]

Yes, it is not reproducible with Java. At least with my test code:

@JsonIgnoreProperties(ignoreUnknown = true)
class Value {
    String type;

    @JsonTypeInfo(
            use = JsonTypeInfo.Id.NAME,
            include = JsonTypeInfo.As.EXTERNAL_PROPERTY,
            property = "type",
            defaultImpl = Default.class
    )
    Default data;
}

class Default {}

String data = "[{\"type\": \"test\",\"data\": {},\"additional\": {}}]";
ObjectMapper mapper = new ObjectMapper();
List<Value> result = mapper.readValue(data, new TypeReference<List<Value>>() {});

[cowtowncoder]

Thank you for verifying: this should help in pinpointing the problem.

[ashlanderr]

I think the problem is here. This forEach loop reads only fields required for constructor invocation. So if an object contains other fields, then they will not be read, and JsonParser will be at END_OBJECT token. The CollectionDeserializer higher in the call stack (here) don't expect that and tries to read another object.

I'll try to submit a pull request that fixes it.

[ashlanderr]

I was wrong. It the KotlinValueInstantiator there is no way to read the object to the end. That must happen here, but it is not checking for ignoreAllUnknown value.

[ashlanderr]

With this new knowledge I was able to reproduce the issue with Java:

@JsonIgnoreProperties(ignoreUnknown = true)
class Value {
    private String type;

    @JsonTypeInfo(
        use = JsonTypeInfo.Id.NAME,
        include = JsonTypeInfo.As.EXTERNAL_PROPERTY,
        property = "type",
        defaultImpl = Default.class
    )
    private Default data;

    @JsonCreator
    public Value(
        @JsonProperty(value = "type", required = true) String type,
        @JsonProperty(value = "data", required = true) Default data
    ) {
        this.type = type;
        this.data = data;
    }
}

class Default {}

String data = "[{\"type\": \"test\",\"data\": {},\"additional\": {}}]";
ObjectMapper mapper = new ObjectMapper();
List<Value> result = mapper.readValue(data, new TypeReference<List<Value>>() {});

The key difference here is to use the constructor for deserialization and require all properties. If properties are not required then the deserializer will put the second empty Value object in the result list, that still is an error.

So it's a Java issue. @cowtowncoder could you transfer it back?

[cowtowncoder]

@ashlanderr Yes, thank you for reproduction, will transfer.