DATAMONGO-2153 - Aggregation support for repositories.

[christophstrobl]

The repository layer offers means interact with the aggregation framework via annotated repository finder methods. Similar to the JSON based queries a pipeline can be defined via the @Aggregation annotation. The definition may contain simple placeholders like ?0 as well as SpEL expression markers ?#{ ... }.

Sync

public interface PersonRepository extends CrudRepository<Person, String> {

  @Aggregation("{ $group: { _id : $lastname, names : { $addToSet : $?0 } } }")
  List<PersonAggregate> groupByLastnameAnd(String property);

  @Aggregation("{ $group: { _id : $lastname, names : { $addToSet : $firstname } } }")
  List<PersonAggregate> groupByLastnameAndFirstnames(Sort sort);

  @Aggregation("{ $group: { _id : $lastname, names : { $addToSet : $?0 } } }")
  List<PersonAggregate> groupByLastnameAnd(String property, Pageable page);

  @Aggregation("{ $group : { _id : null, total : { $sum : $age } } }")
  SumValue sumAgeUsingValueWrapper();

  @Aggregation("{ $group : { _id : null, total : { $sum : $age } } }")
  Long sumAge();

  @Aggregation("{ $group : { _id : null, total : { $sum : $age } } }")
  AggregationResults<SumValue> sumAgeRaw();

  @Aggregation("{ '$project': { '_id' : '$lastname' } }")
  List<String> findAllLastnames();
}

Reactive

public interface ReactivePersonRepository extends ReactiveCrudReppsitory<Person, String> {

  @Aggregation("{ $group: { _id : $lastname, names : { $addToSet : $?0 } } }")
  Flux<PersonAggregate> groupByLastnameAnd(String property);

  @Aggregation("{ $group : { _id : null, total : { $sum : $age } } }")
  Mono<Long> sumAge();

  @Aggregation("{ '$project': { '_id' : '$lastname' } }")
  Flux<String> findAllLastnames();
}

[mp911de]

That's merged and polished now.