Spring Data: JPA repository findAll() to return *Map instead of List?

Question

I have a Spring Data JPA repository interface that looks something like this:

@Repository
public interface DBReportRepository extends JpaRepository<TransactionModel, Long> {

    List<TransactionModel> findAll();
    List<TransactionModel> findByClientId(Long id);
}

Is there a workaround to make the same but for a Collection to be returned of type HashMap<K, V>? I've looked through the Spring Data classes and couldn't find anything other than List<> return values.

Answer 1

I dont think you will find an easier solution as to create a simple one liner to convert your result to a map. It is simple and fast with java 8 lambdas:

Map<Long, Transaction> transactionMap = transactionList.stream()
         .collect(Collectors.toMap(Transaction::getId, Function.identity()));

Answer 2

Just had to solve something similar and Patricks answer helped but it can be improved by indicating where to add it.

To to make it appear like the JPA repo returns a map, an improvement would to wrap this up in a default method in the repository interface. Saves you having to perform a stream in all the consuming classes.

@Repository
public interface DBReportRepository extends JpaRepository<TransactionModel, Long> {

    List<TransactionModel> findAll();

    default Map<Long, TransactionModel> findAllMap() {
        return findAll().stream().collect(Collectors.toMap(TransactionModel::getId, v -> v));
    }

    List<TransactionModel> findByClientId(Long id);

    default Map<Long, TransactionModel> findByClientIdMap(Long id) {
        return findByClientId(id).stream().collect(Collectors.toMap(TransactionModel::getId, v -> v));
    }
}