Add RecordUnmapper construction API

[lukaseder]

This feature extends #2520:

It should be possible to implement an "unmapper" by pairing Field and Function as such:

// R is the target record type, E is the user POJO type
interface RecordUnmapper<E, R extends Record> {
  <T> RecordUnmapper<E, R> add(Field<T> field, Function<E, T> function);
}

This can then be used as such:

unMapper
    .add(field("COL1"), e -> e.getCol1().value)
    .add(field("COL2"), PojoClass::getCol2);

---

See also:
https://groups.google.com/d/msg/jooq-user/7hfDlmEwfQI/Z_F86FM0CAAJ

[steinard]

I am very interested in this functionality.

[thomasgillet]

I would be interested too. I use my own TwoWayFieldMapper, which is both a RecorMapper and RecordUnmapper. Could help if the unmapping part was natively supported by jOOQ.

Here a simplified version:

public interface TwoWayMapper<R extends Record, E> extends RecordMapper<R, E> {
	public R unmap(E e);
}

public class TwoWayFieldMapper<R extends Record, E> implements TwoWayMapper<R, E> {
	
	private final Supplier<R> rFactory;
	private final Supplier<E> eFactory;
	private BiConsumer<R, E> r2e = null;
	private BiConsumer<E, R> e2r = null;
	
	public TwoWayFieldMapper(Supplier<R> rFactory, Supplier<E> eFactory) {
		this.rFactory = rFactory;
		this.eFactory = eFactory;
	}

	public <T> TwoWayFieldMapper<R, E> add(Field<T> field, Function<E, T> getter, BiConsumer<E, T> setter) {
		return add(
			(r, e) -> setter.accept(e, r.get(field)),
			(e, r) -> r.set(field, getter.apply(e))
		);
	}
	
	// Here there is room for various helpers:
	// - converter support (since Converter already works both ways),
	// - "embedded" classes (which already exists to some degree in DefaultRecordMapper),
	// - nested results...
	
	private TwoWayFieldMapper<R, E> add(BiConsumer<R, E> from, BiConsumer<E, R> to) {
		r2e = r2e == null ? from : r2e.andThen(from);
		e2r = e2r == null ? to : e2r.andThen(to);
		return this;
	}
	
	@Override
	public E map(R record) {
		E e = eFactory.get();
		r2e.accept(record, e);
		return e;
	}

	@Override
	public R unmap(E e) {
		R r = rFactory.get();
		e2r.accept(e, r);
		return r;
	}
}

[lukaseder]

Yeah, perhaps that sort of utility will be useful later on. Thanks for sharing.

[lukaseder]

#2520 is now implemented for 3.10. We can now look into implementing this.