Add support for basic operations on Repository interface

[gabrieldn]

It would be useful if the library provided basic operations like count, exists, delete, findOne and findAll given a criteria, sort or pageable. The interface could look something like this:

public interface R2dbcRepository<T, ID> extends ReactiveCrudRepository<T, ID> {
    Mono<Long> count(Criteria criteria);

    Mono<Boolean> exists(Criteria criteria);

    Mono<Void> delete(Criteria criteria);

    Mono<T> findOne(Criteria criteria);

    Flux<T> findAll(Criteria criteria);

    Flux<T> findAll(Sort sort);

    Flux<T> findAll(Criteria criteria, Sort sort);

    Mono<Page<T>> findAll(Pageable pageable);

    Mono<Page<T>> findAll(Criteria criteria, Pageable pageable);
}

There is support for this kind of methods on spring-data-jpa. It would be cool if r2dbc also supported it. The implementation should be pretty straight forward using the api available on R2dbcEntityOperations, which is already available on the SimpleR2dbcRepository.

[odrotbohm]

Criteria is a store specific type and thus shouldn't appear in the repositories interface as it would leak the underlying data access technology into clients. The repositories responsibility is to avoid that exactly. R2dbcEntityOperations are basically that and can be used to implement an API like that inside a repository.

[mp911de]

Closing as per Ollie's comment.

[gabrieldn]

I see, I didn't notice it. In that case, would it be considered to provide such functionality with Example?

Also, as this is related to the issue, is there any reason why Sort and Pageable are not provided in the repository interfaces?

If any of those are acceptable I can create separated issues for them, so the issues are more focussed.

[mp911de]

We have a reactive QueryByExample executor so we could add support for query by example. Can you file a new ticket to start with a fresh history? We would add query by example support also for Spring Data JDBC.

[ogomaemmanuel]

Criteria is a store specific type and thus shouldn't appear in the repositories interface as it would leak the underlying data access technology into clients. The repositories responsibility is to avoid that exactly. R2dbcEntityOperations are basically that and can be used to implement an API like that inside a repository

Just for Curiosity sake, I am learning DDD, does this mean that using Specification as used mostly in spring data JPA is not right