Deserialization of @JsonTypeInfo annotated type fails with missing type id even for explicit concrete subtypes · Issue #2968 · FasterXML/jackson-databind (original) (raw)

When attempting to deserialize to a concrete class that is part of a polymorphic type hierarchy, an InvalidTypeIdException is thrown if the JSON does not contain the type id field. Example:

@JsonTypeInfo( use = JsonTypeInfo.Id.NAME, property = "type") @JsonSubTypes({ @JsonSubTypes.Type(value = Foo.class, name = "foo"), @JsonSubTypes.Type(value = Bar.class, name = "bar")}) public interface Base {}

public class Foo implements Base {}

public class Bar implements Base {}

ObjectMapper mapper = new ObjectMapper();

mapper.readerFor(Foo.class).readValue("{}"); // throws InvalidTypeIdException mapper.readValue("{}", Foo.class); // throws InvalidTypeIdException

While I understand why this happens, as Jackson is finding the JsonTypeInfo / JsonSubTypes annotations on the interface, it is counterintuitive to me. In this instance, I am instructing the mapper as to the specific concrete class to deserialize to, so consulting those annotations seems unnecessary. Perhaps checking if the class / type supplied to readerFor / readValue matches exactly one of the classes listed in JsonSubType could be a fallback if the type id property is not found?

So far, the only workaround I've found is to do something like this:

@JsonTypeInfo(use = JsonTypeInfo.Id.NONE) public class Foo implements Base {}

but then that means serializing a Foo instance would not get the type id property. Perhaps a custom TypeIdResolver or SubTypeResolver could also be used, but having the described behavior baked in seems like a sensible default to me. Thoughts?