Cannot create map from two connected entities in Java

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I have the following entities (unnecessary parts are omitted for brevity):

public class Site {

    private UUID uuid;

    private UUID countryUuid;
}


public class Country {

    private UUID uuid;

    @Column(nullable = false)
    private String name;

    @Column(nullable = false)
    private String code;

    @Column(nullable = false)
    private Currency currency;
}

I have List<UUID> of Site and try to create Map<UUID, Currency> for siteUuid and Currency pair. I have tried something as shown below in order to go by using country list but have not managed.

// get site list
final List<SiteDTO> siteList = siteService.findAllByUuidIn(siteUuidList);

// then get country list
final List<CountryDTO> countryList = siteList.stream()
      .map(SiteDTO::getCountry).collect(Collectors.toList());

// then finall try to map them to Currency
final Map<UUID, CountryDTO> uuidCurrencyMap = countryList
      .stream().collect(Collectors.toMap(CountryDTO::getUuid, Function.identity()));

However, uuidCurrencyMap gives countryUuid - Currency pairs, but I need siteUuid - Currency pairs. So, is it possible?

java-stream hashmap lambda stream java
1 Answers

The following should work:

List<SiteDTO> siteList = siteService.findAllByUuidIn(siteUuidList);
Map<UUID, Currency> siteCurrency = siteList.stream()
  .collect(Collectors.toMap(SiteDTO::getUuid, siteDTO -> siteDTO.getCountry().getCurrency()));
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