Introduce @Lookup methods on repository

[quaff]

After this commit, we could lookup beans from BeanFactory and use them in default methods.

interface FooRepository extends CrudRepository<Foo, Long> {

	default void doSomething(Long fooId, Long barId) {
		Optional<Foo> foo = findById(fooId);
		Optional<Bar> bar = barRepository().findById(barId);
		//TODO do something with foo and bar
	}

	@Lookup
	BarRepository barRepository();
}

interface BarRepository extends CrudRepository<Bar, Long> {

}

[mp911de]

That's not how we want our code to be used. You're mixing concerns of a bean container with public API. Use custom repository fragments with @Autowired instead.

[quaff]

Or we could narrow the type only accept EntityManager and Repository.

interface FooRepository extends CrudRepository<Foo, Long> {

	default void doSomething(Long fooId) {
		EntityManager entityManager = entityManager();
		//TODO do something with entityManager and fooId
	}

	@Lookup
	EntityManager entityManager();
}

It's more concise compare to custom repository fragments, WDYT?

[quaff]

@mp911de Could you guide me the easiest way to implement such extension at application side, customizing repositoryFactoryBeanClass of @EnableJpaRepositories seems viable but not easy because currently there are not enough extension points, some methods are private and some codes should be extracted to protected method to allow override.