Unable to deserialize (extended) Schema

[sebfz1]

Hi,

It appears that it's not possible to deserialize a schema into an extended ObjectSchema class (ie: class MySchema extends ObjectSchema)

java.lang.IllegalArgumentException: Class com.fasterxml.jackson.module.jsonSchema.types.ObjectSchema is not assignable to com.github.issue.MySchema
    at com.fasterxml.jackson.databind.JavaType._assertSubclass(JavaType.java:408)
    at com.fasterxml.jackson.databind.JavaType.narrowBy(JavaType.java:148)
    at com.fasterxml.jackson.databind.jsontype.impl.TypeDeserializerBase._findDeserializer(TypeDeserializerBase.java:179)
    at com.fasterxml.jackson.databind.jsontype.impl.AsPropertyTypeDeserializer._deserializeTypedForId(AsPropertyTypeDeserializer.java:99)
    at com.fasterxml.jackson.databind.jsontype.impl.AsPropertyTypeDeserializer.deserializeTypedFromObject(AsPropertyTypeDeserializer.java:84)
    at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeWithType(BeanDeserializerBase.java:948)
    at com.fasterxml.jackson.databind.deser.impl.TypeWrappedDeserializer.deserialize(TypeWrappedDeserializer.java:41)
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:3051)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2146)
    at com.github.issue.TestSchema.testSchema(TestSchema.java:28)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)

Thanks!
Sebastien

[sebfz1]

Here is the unit test:
https://github.com/sebfz1/jackson-issues/tree/master/issue-67

[cowtowncoder]

Ok, first things first: the immediate reason for failure is use of type 'object', which will result in basic ObjectSchema being deserialized.

But adding handling of this new type is more involved. I'll see if I can figure that out, and if so, will add instructions for doing that.

[cowtowncoder]

Sample implementation will be found from 'src/test/java/com/fasterxml/jackson/module/jsonSchema/CustomSchemaReadTest.java'. Here are the things needed:

    @JsonTypeIdResolver(MyResolver.class)
    public static class MySchema extends ObjectSchema { }

    static class MyResolver extends JsonSchemaIdResolver
    {
        @Override
        public String idFromValue(Object value) {
            if (value instanceof MySchema) {
                return "CUSTOM";
            }
            return super.idFromValue(value);
        }

        @Override
        public String idFromValueAndType(Object value, Class<?> suggestedType) {
            if (value instanceof MySchema) {
                return "CUSTOM";
            }
            return super.idFromValueAndType(value, suggestedType);
        }

        @Override
        public JavaType typeFromId(DatabindContext ctxt, String id) {
            if ("CUSTOM".equals(id)) {
                return ctxt.constructType(MySchema.class);
            }
            return super.typeFromId(ctxt, id);
        }
    }

so it just boils down to adding handling for custom type; you can choose whatever id you want, and it would be possible to make this bit more general.

What I do not know is why handling was done this way: standard Jackson mechanism would have been to instead of basic @JsonTypeName without custom id handler. But the original author (this is a contribution) for some reason chose a bit more complex (and less extensible) route.
Perhaps this should be revisited in future.

[sebfz1]

Hi Tatu,

Thank you very much for this!

Best regards,
Sebastien