Handling of polymorphic class members without a separate repository doesn't work [DATAREST-1186]

[spring-projects-issues]

Fabian Günter opened DATAREST-1186 and commented

Hi,
I have a parent class with a polymorphic child member. Adding entities via a Spring-Data-REST repository works fine, but editing (via PATCH) doesn't change the type of the child member, only its attributes.
The parent code is as follows (without getters/setters and some irrelevant JPA annotations):

@Entity
public class Parent {
    @Id
    private Long id;

    @OneToOne(optional = false, cascade = {CascadeType.PERSIST, CascadeType.MERGE}, orphanRemoval = true)
    @JoinColumn(name = "CHILD")
    private Child child;
}

The code of the child is as follows (again, irrelevant fields omitted):

@JsonTypeInfo(use = JsonTypeInfo.Id.CLASS, include = JsonTypeInfo.As.EXISTING_PROPERTY, property = "@type")
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
public abstract class Child {
    // Some common fields, including an ID

    @JsonProperty("@type")
    public String getType() {
        return getClass().getName();
    }
}

The subclasses don't add anything but some simple fields with no references to other entities.
Upon submitting valid JSON to the ParentRepository (extending CrudRepository<Parent, Long>), all fields get merged but the @type property of the child is ignored. This is because of this code in DomainObjectReader:

if (!mappedProperties.hasPersistentPropertyForField(fieldName)) {
    continue;
}

The @type property is obviously not a persistent property, so it gets ignored.
Is there a fix for this or am I missing anything?

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Affects: 2.6.9 (Ingalls SR9)