refactor(community,tariff): fix code review findings - redundant DB queries, inconsistent imports, overly broad cascade

- TariffService: extract ValidatedUserTariffPoints record from validateUserTariffRequest to eliminate redundant MeteringPoint loads in createUserTariff/updateUserTariff (saves 2 SELECT queries per create call)
- TariffService: move source != target check into validateUserTariffRequest for single-responsibility
- MeteringPoint: restrict CascadeType from ALL to PERSIST/MERGE and remove orphanRemoval to prevent accidental cascade deletes of independent Memberships
- MeteringPointService, MembershipService, MeteringDataService, TariffInviteService, TariffService: replace FQ org.springframework.security.access.AccessDeniedException with imported short form for consistency

eeg_backend/src/main/java/at/mueller/eeg/backend/community/domain/MeteringPoint.java

@@ -48,7 +48,7 @@ public class MeteringPoint {
     @Column(nullable = false)
     private MakoState makoState = MakoState.NEW;
 
-    @OneToMany(mappedBy = "meteringPoint", cascade = CascadeType.ALL, orphanRemoval = true)
+    @OneToMany(mappedBy = "meteringPoint", cascade = {CascadeType.PERSIST, CascadeType.MERGE})
     private List<Membership> memberships;
 
     public void fireTrigger(MakoTrigger trigger) {

eeg_backend/src/main/java/at/mueller/eeg/backend/community/service/MembershipService.java

@@ -16,6 +16,7 @@ import at.mueller.eeg.backend.iam.domain.User;
 import at.mueller.eeg.backend.iam.repository.UserRepository;
 import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
+import org.springframework.security.access.AccessDeniedException;
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
 
@@ -59,7 +60,7 @@ public class MembershipService {
                 .orElseThrow(() -> new IllegalArgumentException("Zählpunkt nicht gefunden"));
 
         if (!point.getUserId().equals(userId)) {
-            throw new org.springframework.security.access.AccessDeniedException("Keine Berechtigung für diesen Zählpunkt.");
+            throw new AccessDeniedException("Keine Berechtigung für diesen Zählpunkt.");
         }
 
         EnergyCommunity community = energyCommunityRepository.findById(request.energyCommunityId())

eeg_backend/src/main/java/at/mueller/eeg/backend/community/service/MeteringDataService.java

@@ -11,6 +11,7 @@ import at.mueller.eeg.backend.community.repository.MeteringDataUploadRepository;
 import at.mueller.eeg.backend.community.repository.MeteringPointRepository;
 import jakarta.persistence.EntityManager;
 import lombok.RequiredArgsConstructor;
+import org.springframework.security.access.AccessDeniedException;
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
 
@@ -113,7 +114,7 @@ public class MeteringDataService {
     private void verifyOwnership(UUID userId, UUID meteringPointId) {
         meteringPointRepository.findById(meteringPointId)
                 .filter(mp -> mp.getUserId().equals(userId))
-                .orElseThrow(() -> new org.springframework.security.access.AccessDeniedException(
+                .orElseThrow(() -> new AccessDeniedException(
                         "Keine Berechtigung zum Zugriff auf diesen Zählpunkt"));
     }
 

eeg_backend/src/main/java/at/mueller/eeg/backend/community/service/MeteringPointService.java

@@ -14,6 +14,7 @@ import at.mueller.eeg.backend.iam.domain.User;
 import at.mueller.eeg.backend.iam.repository.UserRepository;
 import lombok.RequiredArgsConstructor;
 import org.springframework.context.ApplicationEventPublisher;
+import org.springframework.security.access.AccessDeniedException;
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
 
@@ -76,7 +77,7 @@ public class MeteringPointService {
                 .orElseThrow(() -> new IllegalArgumentException("Zählpunkt nicht gefunden"));
 
         if (!point.getUserId().equals(userId)) {
-            throw new org.springframework.security.access.AccessDeniedException("Keine Berechtigung zum Bearbeiten dieses Zählpunkts");
+            throw new AccessDeniedException("Keine Berechtigung zum Bearbeiten dieses Zählpunkts");
         }
 
         if (point.getMakoState() != MakoState.NEW && point.getMakoState() != MakoState.REJECTED && point.getMakoState() != MakoState.ERROR) {
@@ -107,7 +108,7 @@ public class MeteringPointService {
                 .orElseThrow(() -> new IllegalArgumentException("Zählpunkt nicht gefunden"));
 
         if (!point.getUserId().equals(userId)) {
-            throw new org.springframework.security.access.AccessDeniedException("Keine Berechtigung zum Löschen dieses Zählpunkts");
+            throw new AccessDeniedException("Keine Berechtigung zum Löschen dieses Zählpunkts");
         }
 
         if (point.getMakoState() == MakoState.ACTIVE) {

eeg_backend/src/main/java/at/mueller/eeg/backend/tariff/service/TariffInviteService.java

@@ -9,6 +9,7 @@ import at.mueller.eeg.backend.tariff.domain.TariffInvite;
 import at.mueller.eeg.backend.tariff.repository.TariffInviteRepository;
 import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
+import org.springframework.security.access.AccessDeniedException;
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
 
@@ -78,7 +79,7 @@ public class TariffInviteService {
                 .orElseThrow(() -> new IllegalArgumentException("Einladung nicht gefunden: " + inviteId));
 
         if (!invite.getConsumerUserId().equals(consumerUserId)) {
-            throw new org.springframework.security.access.AccessDeniedException(
+            throw new AccessDeniedException(
                     "Keine Berechtigung zum Annehmen dieser Einladung.");
         }
         if (invite.getStatus() != InviteStatus.PENDING) {

eeg_backend/src/main/java/at/mueller/eeg/backend/tariff/service/TariffService.java

@@ -20,6 +20,7 @@ import at.mueller.eeg.backend.tariff.repository.UserTariffRepository;
 import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
 import org.springframework.context.ApplicationEventPublisher;
+import org.springframework.security.access.AccessDeniedException;
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
 
@@ -73,10 +74,6 @@ public class TariffService {
 
     @Transactional
     public UserTariffResponse createUserTariff(UUID userId, UserTariffRequest request) {
-        if (request.sourceMeteringPointId().equals(request.targetMeteringPointId())) {
-            throw new IllegalStateException("Quell- und Ziel-Zählpunkt müssen unterschiedlich sein.");
-        }
-
         userTariffRepository.findBySourceMeteringPointIdAndTargetMeteringPointId(
                 request.sourceMeteringPointId(), request.targetMeteringPointId())
                 .ifPresent(existing -> {
@@ -84,17 +81,10 @@ public class TariffService {
                             "Es existiert bereits ein Tarif zwischen diesen beiden Zählpunkten.");
                 });
 
-        validateUserTariffRequest(request.energyCommunityId(), request);
+        ValidatedUserTariffPoints validated = validateUserTariffRequest(request.energyCommunityId(), request);
-
-        MeteringPoint sourcePoint = meteringPointRepository.findById(request.sourceMeteringPointId())
-                .orElseThrow(() -> new IllegalArgumentException(
-                        "Quell-Zählpunkt nicht gefunden: " + request.sourceMeteringPointId()));
-        MeteringPoint targetPoint = meteringPointRepository.findById(request.targetMeteringPointId())
-                .orElseThrow(() -> new IllegalArgumentException(
-                        "Ziel-Zählpunkt nicht gefunden: " + request.targetMeteringPointId()));
 
         if (!tariffInviteRepository.existsByProducerUserIdAndConsumerUserIdAndEnergyCommunityIdAndStatus(
-                sourcePoint.getUserId(), targetPoint.getUserId(), request.energyCommunityId(), InviteStatus.ACCEPTED)) {
+                validated.source().getUserId(), validated.target().getUserId(), request.energyCommunityId(), InviteStatus.ACCEPTED)) {
             throw new IllegalStateException(
                     "Zwischen Produzent und Konsument muss eine angenommene Einladung bestehen.");
         }
@@ -113,7 +103,7 @@ public class TariffService {
                 request.targetMeteringPointId(), request.pricePerKwhCents());
 
         eventPublisher.publishEvent(new UserTariffChangedEvent(
-                request.energyCommunityId(), sourcePoint.getUserId(), targetPoint.getUserId(), "CREATED"));
+                request.energyCommunityId(), validated.source().getUserId(), validated.target().getUserId(), "CREATED"));
 
         return toUserTariffResponse(saved);
     }
@@ -127,18 +117,11 @@ public class TariffService {
                 .orElseThrow(() -> new IllegalArgumentException("Quell-Zählpunkt nicht gefunden."));
 
         if (!sourcePoint.getUserId().equals(userId)) {
-            throw new org.springframework.security.access.AccessDeniedException(
+            throw new AccessDeniedException(
                     "Keine Berechtigung zum Bearbeiten dieses Tarifs.");
         }
 
-        if (request.sourceMeteringPointId().equals(request.targetMeteringPointId())) {
+        ValidatedUserTariffPoints validated = validateUserTariffRequest(request.energyCommunityId(), request);
-            throw new IllegalStateException("Quell- und Ziel-Zählpunkt müssen unterschiedlich sein.");
-        }
-
-        validateUserTariffRequest(request.energyCommunityId(), request);
-
-        MeteringPoint newTargetPoint = meteringPointRepository.findById(request.targetMeteringPointId())
-                .orElseThrow(() -> new IllegalArgumentException("Ziel-Zählpunkt nicht gefunden."));
 
         tariff.setEnergyCommunityId(request.energyCommunityId());
         tariff.setSourceMeteringPointId(request.sourceMeteringPointId());
@@ -152,7 +135,7 @@ public class TariffService {
                 tariffId, request.pricePerKwhCents());
 
         eventPublisher.publishEvent(new UserTariffChangedEvent(
-                request.energyCommunityId(), sourcePoint.getUserId(), newTargetPoint.getUserId(), "UPDATED"));
+                request.energyCommunityId(), sourcePoint.getUserId(), validated.target().getUserId(), "UPDATED"));
 
         return toUserTariffResponse(saved);
     }
@@ -166,7 +149,7 @@ public class TariffService {
                 .orElseThrow(() -> new IllegalArgumentException("Quell-Zählpunkt nicht gefunden."));
 
         if (!sourcePoint.getUserId().equals(userId)) {
-            throw new org.springframework.security.access.AccessDeniedException(
+            throw new AccessDeniedException(
                     "Keine Berechtigung zum Löschen dieses Tarifs.");
         }
 
@@ -214,7 +197,13 @@ public class TariffService {
         );
     }
 
-    private void validateUserTariffRequest(UUID communityId, UserTariffRequest request) {
+    record ValidatedUserTariffPoints(MeteringPoint source, MeteringPoint target) {}
+
+    private ValidatedUserTariffPoints validateUserTariffRequest(UUID communityId, UserTariffRequest request) {
+        if (request.sourceMeteringPointId().equals(request.targetMeteringPointId())) {
+            throw new IllegalStateException("Quell- und Ziel-Zählpunkt müssen unterschiedlich sein.");
+        }
+
         MeteringPoint sourcePoint = meteringPointRepository.findById(request.sourceMeteringPointId())
                 .orElseThrow(() -> new IllegalArgumentException(
                         "Quell-Zählpunkt nicht gefunden: " + request.sourceMeteringPointId()));
@@ -248,5 +237,7 @@ public class TariffService {
         if (!membershipRepository.isActiveMemberOfCommunity(targetUserId, communityId)) {
             throw new IllegalStateException("Ziel-Benutzer ist kein Mitglied der Energiegemeinschaft.");
         }
+
+        return new ValidatedUserTariffPoints(sourcePoint, targetPoint);
     }
 }