DATAJDBC-557 - Save entity only have id and collections throws exception.

[lseeker]

DATAJDBC-557

Entity like

class DummyEntity {
	@Id private Long id;
	Set<Element> content = new HashSet<>();
}

generates invalid sql on InsertRoot and UpdateRoot.

This pull request fixes by include id column when no columns exists on aggregate root.

[schauder]

This doesn't work so easy.

At least some databases don't allow to provide null for a generated field, e.g. Postgress will try to write the null value actually to the database. DEFAULT probably does the trick there. See https://stackoverflow.com/a/12836448/66686

Therefore I guess we need to extend the dialect to provide information how to handle this case and then act accordingly when performing inserts/updates.

I rebased the current PR and pushed it as https://github.com/spring-projects/spring-data-jdbc/tree/pr/datajdbc-557

See https://github.com/spring-projects/spring-data-jdbc/tree/pr/datajdbc-557#running-integration-tests for how to run integration tests locally.

[schauder]

As mentioned in the previous comment, the current approach does not work.