add @EmbeddableResult

[gavinking]

Section 3.10.16.1 of the spec specifies that embeddable objects returned by native queries are handled by specifying a property path using the name member of @FieldResult. For example:

@SqlResultSetMapping(name=”CustomerResults”, 
    entities=@EntityResult(entityClass=Customer.class, 
        fields={@FieldResult(name="id", column="customer_id"),
                @FieldResult(name="address.street", column="customer_street"),
                @FieldResult(name="address.city", column="customer_city"),
                @FieldResult(name="address.state", column="customer_state"),
                @FieldResult(name="status", column="customer_status")}
)

This works but somehow I always found it slightly weird, bordering on inelegant, that, given that @Embeddable objects are a basic construct in the type system of JPA, there was no corresponding @EmbeddableResult annotation.

@SqlResultSetMapping(name=”CustomerResults”, 
    entities=@EntityResult(entityClass=Customer.class, 
        fields={@FieldResult(name="id", column="customer_id"),
                @FieldResult(name="status", column="customer_status")},
        embeddables=@EmbeddableResult(name = address,
            fields={@FieldResult(name="street", column="customer_street"),
                    @FieldResult(name="city", column="customer_city"),
                    @FieldResult(name="state", column="customer_state")}))
)

Is that better? Maybe not. We all hate nested annotations in Java!

But in light of #459, this code example can easily be made typesafe, whereas the first cannot:

@SqlResultSetMapping(name=”CustomerResults”, 
    entities=@EntityResult(entityClass=Customer.class, 
        fields={@FieldResult(name=Customer_.ID, column="customer_id"),
                @FieldResult(name=Customer_.STATUS, column="customer_status")},
        embeddables=@EmbeddableResult(name = address,
            fields={@FieldResult(name=Address_.STREET, column="customer_street"),
                    @FieldResult(name=Address_.CITY, column="customer_city"),
                    @FieldResult(name=Address_.STATE, column="customer_state")}))
)

And this is, in my opinion, sufficient reason to add such an annotation to JPA.

[gavinking]

Note that this enhancement is also, IMO, needed in order to do #9 in an elegant way.

[gavinking]

A limitation here, and, perhaps, an argument against doing it all, is that due to Java language limitations, nested @EmbeddableResults would not be allowed. That's annoying.