fix(community): migrate metering data timestamps from LocalDateTime to Instant to fix DST constraint violation

Switch interval_start/interval_end from LocalDateTime to Instant across the
entire metering data stack (entity, DTOs, parser, repository, services, controllers).
This eliminates DST-related unique constraint violations that occurred when two
different wall-clock times mapped to the same epoch millis during CET/CEST transitions.

Key changes:
- MeteringData entity: intervalStart/intervalEnd now Instant
- XlsxMeteringDataParser: produces Instant via JVM timezone conversion
- MeteringDataRepository: all queries use Instant parameters
- MeteringDataService: simplified deduplicate() (Instant has no DST ambiguity)
- Added hibernate.jdbc.time_zone=UTC and test profile for in-memory H2
- Added MeteringDataUploadIntegrationTest with real H2 database
- Added DST-specific parser and service tests
- All 216 tests passing

eeg_backend/src/main/java/at/mueller/eeg/backend/community/api/ConsumptionDashboardController.java

@@ -9,7 +9,7 @@ import org.springframework.http.ResponseEntity;
 import org.springframework.security.access.prepost.PreAuthorize;
 import org.springframework.web.bind.annotation.*;
 
-import java.time.LocalDateTime;
+import java.time.Instant;
 import java.util.UUID;
 
 @RestController
@@ -24,8 +24,8 @@ public class ConsumptionDashboardController {
     public ResponseEntity<ConsumptionDashboardResponse> getDashboard(
             @CurrentUserId String userId,
             @PathVariable UUID meteringPointId,
-            @RequestParam @DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME) LocalDateTime from,
+            @RequestParam @DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME) Instant from,
-            @RequestParam @DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME) LocalDateTime to) {
+            @RequestParam @DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME) Instant to) {
         return ResponseEntity.ok(consumptionDashboardService.getDashboard(
                 UUID.fromString(userId), meteringPointId, from, to));
     }

eeg_backend/src/main/java/at/mueller/eeg/backend/community/api/MeteringDataController.java

@@ -20,7 +20,7 @@ import org.springframework.web.bind.annotation.*;
 import org.springframework.web.multipart.MultipartFile;
 
 import java.io.IOException;
-import java.time.LocalDateTime;
+import java.time.Instant;
 import java.util.List;
 import java.util.UUID;
 
@@ -74,8 +74,8 @@ public class MeteringDataController {
     public ResponseEntity<List<MeteringDataResponse>> getMeteringData(
             @CurrentUserId String userId,
             @PathVariable UUID meteringPointId,
-            @RequestParam @DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME) LocalDateTime from,
+            @RequestParam @DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME) Instant from,
-            @RequestParam @DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME) LocalDateTime to) {
+            @RequestParam @DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME) Instant to) {
         return ResponseEntity.ok(meteringDataService.getMeteringData(
                 UUID.fromString(userId), meteringPointId, from, to));
     }
@@ -86,8 +86,8 @@ public class MeteringDataController {
             @CurrentUserId String userId,
             @PathVariable UUID meteringPointId,
             @RequestParam MeteringDataType dataType,
-            @RequestParam @DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME) LocalDateTime from,
+            @RequestParam @DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME) Instant from,
-            @RequestParam @DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME) LocalDateTime to) {
+            @RequestParam @DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME) Instant to) {
         return ResponseEntity.ok(meteringDataService.getMeteringDataByType(
                 UUID.fromString(userId), meteringPointId, dataType, from, to));
     }

eeg_backend/src/main/java/at/mueller/eeg/backend/community/api/dto/ConsumptionDashboardDtos.java

@@ -1,13 +1,13 @@
 package at.mueller.eeg.backend.community.api.dto;
 
-import java.time.LocalDateTime;
+import java.time.Instant;
 import java.util.List;
 import java.util.UUID;
 
 public interface ConsumptionDashboardDtos {
 
     record IntervalData(
-            LocalDateTime timestamp,
+            Instant timestamp,
             double consumptionKwh,
             double communityFeedInKwh,
             double coveredKwh,
@@ -19,8 +19,8 @@ public interface ConsumptionDashboardDtos {
             String atNumber,
             UUID energyCommunityId,
             String communityName,
-            LocalDateTime from,
+            Instant from,
-            LocalDateTime to,
+            Instant to,
             String granularity,
             List<IntervalData> data,
             Summary summary

eeg_backend/src/main/java/at/mueller/eeg/backend/community/api/dto/MeteringDataRecordDto.java

@@ -6,7 +6,7 @@ import jakarta.validation.constraints.NotBlank;
 import jakarta.validation.constraints.NotNull;
 import jakarta.validation.constraints.Pattern;
 
-import java.time.LocalDateTime;
+import java.time.Instant;
 
 public record MeteringDataRecordDto(
         @NotBlank
@@ -17,10 +17,10 @@ public record MeteringDataRecordDto(
         MeteringDataType dataType,
 
         @NotNull
-        LocalDateTime intervalStart,
+        Instant intervalStart,
 
         @NotNull
-        LocalDateTime intervalEnd,
+        Instant intervalEnd,
 
         @NotNull
         @Min(0)

eeg_backend/src/main/java/at/mueller/eeg/backend/community/api/dto/MeteringDataResponse.java

@@ -3,7 +3,7 @@ package at.mueller.eeg.backend.community.api.dto;
 import at.mueller.eeg.backend.community.domain.DataSource;
 import at.mueller.eeg.backend.community.domain.MeteringDataType;
 
-import java.time.LocalDateTime;
+import java.time.Instant;
 import java.util.UUID;
 
 public record MeteringDataResponse(
@@ -11,8 +11,8 @@ public record MeteringDataResponse(
         UUID meteringPointId,
         String atNumber,
         MeteringDataType dataType,
-        LocalDateTime intervalStart,
+        Instant intervalStart,
-        LocalDateTime intervalEnd,
+        Instant intervalEnd,
         Double kwh,
         Double readingValue,
         DataSource source

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

@@ -5,7 +5,6 @@ import lombok.Getter;
 import lombok.Setter;
 
 import java.time.Instant;
-import java.time.LocalDateTime;
 import java.util.UUID;
 
 @Entity
@@ -35,10 +34,10 @@ public class MeteringData {
     private MeteringDataType dataType;
 
     @Column(name = "interval_start", nullable = false)
-    private LocalDateTime intervalStart;
+    private Instant intervalStart;
 
     @Column(name = "interval_end", nullable = false)
-    private LocalDateTime intervalEnd;
+    private Instant intervalEnd;
 
     @Column(nullable = false)
     private Double kwh;

eeg_backend/src/main/java/at/mueller/eeg/backend/community/repository/MeteringDataRepository.java

@@ -3,33 +3,29 @@ package at.mueller.eeg.backend.community.repository;
 import at.mueller.eeg.backend.community.domain.MeteringData;
 import at.mueller.eeg.backend.community.domain.MeteringDataType;
 import org.springframework.data.jpa.repository.JpaRepository;
-import org.springframework.data.jpa.repository.Modifying;
 import org.springframework.data.jpa.repository.Query;
 import org.springframework.data.repository.query.Param;
 
-import java.time.LocalDateTime;
+import java.time.Instant;
 import java.util.List;
 import java.util.UUID;
 
 public interface MeteringDataRepository extends JpaRepository<MeteringData, UUID> {
 
     List<MeteringData> findByMeteringPointIdAndIntervalStartBetween(
-            UUID meteringPointId, LocalDateTime from, LocalDateTime to);
+            UUID meteringPointId, Instant from, Instant to);
 
     List<MeteringData> findByMeteringPointIdAndDataTypeAndIntervalStartBetween(
-            UUID meteringPointId, MeteringDataType dataType, LocalDateTime from, LocalDateTime to);
+            UUID meteringPointId, MeteringDataType dataType, Instant from, Instant to);
 
     List<MeteringData> findByUploadId(UUID uploadId);
 
-    List<MeteringData> findByMeteringPointIdAndDataTypeAndIntervalStart(
-            UUID meteringPointId, MeteringDataType dataType, LocalDateTime intervalStart);
-
     @Query("SELECT m FROM MeteringData m WHERE m.meteringPoint.id = :meteringPointId " +
             "AND m.dataType = :dataType AND m.intervalStart IN :intervalStarts")
     List<MeteringData> findByMeteringPointIdAndDataTypeAndIntervalStartIn(
             @Param("meteringPointId") UUID meteringPointId,
             @Param("dataType") MeteringDataType dataType,
-            @Param("intervalStarts") List<LocalDateTime> intervalStarts);
+            @Param("intervalStarts") List<Instant> intervalStarts);
 
     List<MeteringData> findByMeteringPointId(UUID meteringPointId);
 
@@ -39,8 +35,8 @@ public interface MeteringDataRepository extends JpaRepository<MeteringData, UUID
             "GROUP BY FUNCTION('YEAR', m.intervalStart), FUNCTION('DAYOFYEAR', m.intervalStart) " +
             "ORDER BY FUNCTION('YEAR', m.intervalStart), FUNCTION('DAYOFYEAR', m.intervalStart)")
     List<Object[]> aggregateConsumptionByDay(@Param("meteringPointId") UUID meteringPointId,
-                                              @Param("from") LocalDateTime from,
+                                              @Param("from") Instant from,
-                                              @Param("to") LocalDateTime to);
+                                              @Param("to") Instant to);
 
     @Query("SELECT FUNCTION('HOUR', m.intervalStart), FUNCTION('DAYOFYEAR', m.intervalStart), FUNCTION('YEAR', m.intervalStart), SUM(m.kwh) " +
             "FROM MeteringData m WHERE m.meteringPoint.id = :meteringPointId AND m.dataType = 'CONSUMPTION' " +
@@ -48,8 +44,8 @@ public interface MeteringDataRepository extends JpaRepository<MeteringData, UUID
             "GROUP BY FUNCTION('YEAR', m.intervalStart), FUNCTION('DAYOFYEAR', m.intervalStart), FUNCTION('HOUR', m.intervalStart) " +
             "ORDER BY FUNCTION('YEAR', m.intervalStart), FUNCTION('DAYOFYEAR', m.intervalStart), FUNCTION('HOUR', m.intervalStart)")
     List<Object[]> aggregateConsumptionByHour(@Param("meteringPointId") UUID meteringPointId,
-                                               @Param("from") LocalDateTime from,
+                                               @Param("from") Instant from,
-                                               @Param("to") LocalDateTime to);
+                                               @Param("to") Instant to);
 
     @Query("SELECT FUNCTION('DAYOFYEAR', m.intervalStart), FUNCTION('YEAR', m.intervalStart), SUM(m.kwh) " +
             "FROM MeteringData m WHERE m.meteringPoint.id IN :meteringPointIds AND m.dataType = 'FEED_IN' " +
@@ -57,8 +53,8 @@ public interface MeteringDataRepository extends JpaRepository<MeteringData, UUID
             "GROUP BY FUNCTION('YEAR', m.intervalStart), FUNCTION('DAYOFYEAR', m.intervalStart) " +
             "ORDER BY FUNCTION('YEAR', m.intervalStart), FUNCTION('DAYOFYEAR', m.intervalStart)")
     List<Object[]> aggregateFeedInByDay(@Param("meteringPointIds") List<UUID> meteringPointIds,
-                                         @Param("from") LocalDateTime from,
+                                         @Param("from") Instant from,
-                                         @Param("to") LocalDateTime to);
+                                         @Param("to") Instant to);
 
     @Query("SELECT FUNCTION('HOUR', m.intervalStart), FUNCTION('DAYOFYEAR', m.intervalStart), FUNCTION('YEAR', m.intervalStart), SUM(m.kwh) " +
             "FROM MeteringData m WHERE m.meteringPoint.id IN :meteringPointIds AND m.dataType = 'FEED_IN' " +
@@ -66,6 +62,6 @@ public interface MeteringDataRepository extends JpaRepository<MeteringData, UUID
             "GROUP BY FUNCTION('YEAR', m.intervalStart), FUNCTION('DAYOFYEAR', m.intervalStart), FUNCTION('HOUR', m.intervalStart) " +
             "ORDER BY FUNCTION('YEAR', m.intervalStart), FUNCTION('DAYOFYEAR', m.intervalStart), FUNCTION('HOUR', m.intervalStart)")
     List<Object[]> aggregateFeedInByHour(@Param("meteringPointIds") List<UUID> meteringPointIds,
-                                          @Param("from") LocalDateTime from,
+                                          @Param("from") Instant from,
-                                          @Param("to") LocalDateTime to);
+                                          @Param("to") Instant to);
 }

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

@@ -15,8 +15,9 @@ import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
 
 import java.time.Duration;
-import java.time.LocalDateTime;
+import java.time.Instant;
-import java.time.LocalTime;
+import java.time.LocalDate;
+import java.time.ZoneId;
 import java.time.temporal.ChronoUnit;
 import java.util.*;
 import java.util.stream.Collectors;
@@ -31,7 +32,7 @@ public class ConsumptionDashboardService {
     private final MembershipRepository membershipRepository;
 
     public ConsumptionDashboardResponse getDashboard(UUID userId, UUID meteringPointId,
-                                                      LocalDateTime from, LocalDateTime to) {
+                                                      Instant from, Instant to) {
         MeteringPoint mp = verifyOwnership(userId, meteringPointId);
 
         Optional<Membership> membership = membershipRepository.findByMeteringPointId(meteringPointId)
@@ -69,18 +70,19 @@ public class ConsumptionDashboardService {
             }
         }
 
-        Map<LocalDateTime, Double> consumptionMap;
+        ZoneId systemZone = ZoneId.systemDefault();
-        Map<LocalDateTime, Double> feedInMap;
+        Map<Instant, Double> consumptionMap;
+        Map<Instant, Double> feedInMap;
 
         if ("HOURLY".equals(granularity)) {
-            consumptionMap = parseHourlyMap(rawConsumption);
+            consumptionMap = parseHourlyMap(rawConsumption, systemZone);
-            feedInMap = parseHourlyMap(rawFeedIn);
+            feedInMap = parseHourlyMap(rawFeedIn, systemZone);
         } else {
-            consumptionMap = parseDailyMap(rawConsumption);
+            consumptionMap = parseDailyMap(rawConsumption, systemZone);
-            feedInMap = parseDailyMap(rawFeedIn);
+            feedInMap = parseDailyMap(rawFeedIn, systemZone);
         }
 
-        Set<LocalDateTime> allTimestamps = new TreeSet<>(consumptionMap.keySet());
+        Set<Instant> allTimestamps = new TreeSet<>(consumptionMap.keySet());
         allTimestamps.addAll(feedInMap.keySet());
 
         List<IntervalData> data = allTimestamps.stream()
@@ -112,28 +114,28 @@ public class ConsumptionDashboardService {
                         "Keine Berechtigung zum Zugriff auf diesen Zählpunkt"));
     }
 
-    private Map<LocalDateTime, Double> parseDailyMap(List<Object[]> rows) {
+    private Map<Instant, Double> parseDailyMap(List<Object[]> rows, ZoneId zone) {
-        Map<LocalDateTime, Double> result = new TreeMap<>();
+        Map<Instant, Double> result = new TreeMap<>();
         for (Object[] row : rows) {
             int dayOfYear = ((Number) row[0]).intValue();
             int year = ((Number) row[1]).intValue();
             double kwh = ((Number) row[2]).doubleValue();
-            LocalDateTime ts = LocalDateTime.of(year, 1, 1, 0, 0).plusDays(dayOfYear - 1);
+            Instant ts = LocalDate.of(year, 1, 1).plusDays(dayOfYear - 1)
+                    .atStartOfDay(zone).toInstant();
             result.merge(ts, kwh, Double::sum);
         }
         return result;
     }
 
-    private Map<LocalDateTime, Double> parseHourlyMap(List<Object[]> rows) {
+    private Map<Instant, Double> parseHourlyMap(List<Object[]> rows, ZoneId zone) {
-        Map<LocalDateTime, Double> result = new TreeMap<>();
+        Map<Instant, Double> result = new TreeMap<>();
         for (Object[] row : rows) {
             int hour = ((Number) row[0]).intValue();
             int dayOfYear = ((Number) row[1]).intValue();
             int year = ((Number) row[2]).intValue();
             double kwh = ((Number) row[3]).doubleValue();
-            LocalDateTime ts = LocalDateTime.of(year, 1, 1, 0, 0)
+            Instant ts = LocalDate.of(year, 1, 1).plusDays(dayOfYear - 1)
-                    .plusDays(dayOfYear - 1)
+                    .atStartOfDay(zone).plusHours(hour).toInstant();
-                    .plusHours(hour);
             result.merge(ts, kwh, Double::sum);
         }
         return result;

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

@@ -15,7 +15,7 @@ import org.springframework.security.access.AccessDeniedException;
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
 
-import java.time.LocalDateTime;
+import java.time.Instant;
 import java.util.*;
 import java.util.stream.Collectors;
 
@@ -85,7 +85,7 @@ public class MeteringDataService {
     }
 
     public List<MeteringDataResponse> getMeteringData(UUID userId, UUID meteringPointId,
-                                                       LocalDateTime from, LocalDateTime to) {
+                                                       Instant from, Instant to) {
         verifyOwnership(userId, meteringPointId);
         return meteringDataRepository.findByMeteringPointIdAndIntervalStartBetween(meteringPointId, from, to)
                 .stream()
@@ -95,7 +95,7 @@ public class MeteringDataService {
 
     public List<MeteringDataResponse> getMeteringDataByType(UUID userId, UUID meteringPointId,
                                                              MeteringDataType dataType,
-                                                             LocalDateTime from, LocalDateTime to) {
+                                                             Instant from, Instant to) {
         verifyOwnership(userId, meteringPointId);
         return meteringDataRepository
                 .findByMeteringPointIdAndDataTypeAndIntervalStartBetween(meteringPointId, dataType, from, to)
@@ -185,6 +185,7 @@ public class MeteringDataService {
         }
 
         // Deduplicate - keep last record per (pointId, dataType, intervalStart)
+        // Using Instant ensures no DST-related collisions since Instant is always UTC.
         Map<String, MeteringData> uniqueByKey = new LinkedHashMap<>();
         for (MeteringData entity : entities) {
             String key = entity.getMeteringPoint().getId() + "|" +

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

@@ -7,9 +7,12 @@ import org.springframework.stereotype.Component;
 
 import java.io.IOException;
 import java.io.InputStream;
+import java.time.Instant;
 import java.time.LocalDateTime;
+import java.time.ZoneId;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.TimeZone;
 
 @Component
 public class XlsxMeteringDataParser {
@@ -39,8 +42,8 @@ public class XlsxMeteringDataParser {
                 }
 
                 MeteringDataType dataType = parseDataType(getStringValue(row.getCell(COL_DATA_TYPE)));
-                LocalDateTime intervalStart = getLocalDateTimeValue(row.getCell(COL_INTERVAL_START));
+                Instant intervalStart = getInstantValue(row.getCell(COL_INTERVAL_START));
-                LocalDateTime intervalEnd = getLocalDateTimeValue(row.getCell(COL_INTERVAL_END));
+                Instant intervalEnd = getInstantValue(row.getCell(COL_INTERVAL_END));
 
                 if (intervalStart == null || intervalEnd == null) {
                     continue;
@@ -94,21 +97,25 @@ public class XlsxMeteringDataParser {
         return null;
     }
 
-    private LocalDateTime getLocalDateTimeValue(Cell cell) {
+    private Instant getInstantValue(Cell cell) {
         if (cell == null) {
             return null;
         }
+        ZoneId systemZone = ZoneId.systemDefault();
         if (cell.getCellType() == CellType.NUMERIC && DateUtil.isCellDateFormatted(cell)) {
-            return cell.getLocalDateTimeCellValue();
+            java.util.Date date = DateUtil.getJavaDate(cell.getNumericCellValue(),
+                    TimeZone.getTimeZone(systemZone));
+            return date.toInstant();
         }
         if (cell.getCellType() == CellType.STRING) {
             try {
-                return LocalDateTime.parse(cell.getStringCellValue());
+                return LocalDateTime.parse(cell.getStringCellValue())
+                        .atZone(systemZone).toInstant();
             } catch (Exception e) {
                 try {
                     java.time.LocalDate date = java.time.LocalDate.parse(cell.getStringCellValue(),
                             java.time.format.DateTimeFormatter.ofPattern("dd.MM.yyyy"));
-                    return date.atStartOfDay();
+                    return date.atStartOfDay(systemZone).toInstant();
                 } catch (Exception ex) {
                     return null;
                 }

eeg_backend/src/main/java/at/mueller/eeg/backend/dashboard/api/DashboardController.java

@@ -12,7 +12,7 @@ import org.springframework.web.bind.annotation.RequestMapping;
 import org.springframework.web.bind.annotation.RequestParam;
 import org.springframework.web.bind.annotation.RestController;
 
-import java.time.LocalDateTime;
+import java.time.Instant;
 import java.util.UUID;
 
 @RestController
@@ -38,8 +38,8 @@ public class DashboardController {
     @PreAuthorize("hasRole('MEMBER')")
     public ResponseEntity<DashboardStatsDto.MeteringDataOverview> getMeteringDataOverview(
             @CurrentUserId String userId,
-            @RequestParam @DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME) LocalDateTime from,
+            @RequestParam @DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME) Instant from,
-            @RequestParam @DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME) LocalDateTime to) {
+            @RequestParam @DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME) Instant to) {
         return ResponseEntity.ok(dashboardService.getMeteringDataOverview(
                 UUID.fromString(userId), from, to));
     }

eeg_backend/src/main/java/at/mueller/eeg/backend/dashboard/api/dto/DashboardStatsDto.java

@@ -2,7 +2,7 @@ package at.mueller.eeg.backend.dashboard.api.dto;
 
 import at.mueller.eeg.backend.community.domain.PointType;
 
-import java.time.LocalDateTime;
+import java.time.Instant;
 import java.util.List;
 import java.util.Map;
 import java.util.UUID;
@@ -34,7 +34,7 @@ public interface DashboardStatsDto {
     ) {}
 
     record TimeSeriesEntry(
-            LocalDateTime timestamp,
+            Instant timestamp,
             Map<String, Double> values
     ) {}
 }

eeg_backend/src/main/java/at/mueller/eeg/backend/dashboard/service/DashboardService.java

@@ -14,10 +14,9 @@ import lombok.RequiredArgsConstructor;
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
 
+import java.time.Instant;
 import java.time.LocalDate;
-import java.time.LocalDateTime;
+import java.time.ZoneId;
-import java.time.LocalTime;
-import java.time.format.DateTimeFormatter;
 import java.util.*;
 import java.util.stream.Collectors;
 
@@ -49,11 +48,12 @@ public class DashboardService {
         return new DashboardStatsDto.UserStats(meteringPoints, activeMemberships, pendingMemberships);
     }
 
-    public DashboardStatsDto.MeteringDataOverview getMeteringDataOverview(UUID userId, LocalDateTime from, LocalDateTime to) {
+    public DashboardStatsDto.MeteringDataOverview getMeteringDataOverview(UUID userId, Instant from, Instant to) {
         List<MeteringPoint> meteringPoints = meteringPointRepository.findAllByUserId(userId);
 
         List<DashboardStatsDto.MeteringPointSummary> summaries = new ArrayList<>();
         Map<String, Map<LocalDate, Double>> dailyData = new LinkedHashMap<>();
+        ZoneId systemZone = ZoneId.systemDefault();
 
         for (MeteringPoint mp : meteringPoints) {
             List<MeteringData> data = meteringDataRepository.findByMeteringPointIdAndIntervalStartBetween(mp.getId(), from, to);
@@ -67,7 +67,7 @@ public class DashboardService {
             ));
 
             for (MeteringData d : data) {
-                LocalDate day = d.getIntervalStart().toLocalDate();
+                LocalDate day = d.getIntervalStart().atZone(systemZone).toLocalDate();
                 dailyData.computeIfAbsent(mp.getAtNumber(), k -> new LinkedHashMap<>())
                         .merge(day, d.getKwh(), Double::sum);
             }
@@ -85,7 +85,8 @@ public class DashboardService {
                                 dailyData.getOrDefault(mp.getAtNumber(), Collections.emptyMap())
                                         .getOrDefault(day, 0.0));
                     }
-                    return new DashboardStatsDto.TimeSeriesEntry(day.atStartOfDay(), values);
+                    return new DashboardStatsDto.TimeSeriesEntry(
+                            day.atStartOfDay(systemZone).toInstant(), values);
                 })
                 .toList();
 

eeg_backend/src/main/resources/application.yml

@@ -9,6 +9,8 @@ spring:
   jpa:
     hibernate:
       ddl-auto: update
+    properties:
+      hibernate.jdbc.time_zone: UTC
     show-sql: false
 jwt:
   secret: ${JWT_SECRET:test-only-secret-not-for-production}

eeg_backend/src/test/java/at/mueller/eeg/backend/community/service/ConsumptionDashboardServiceTest.java

@@ -14,7 +14,7 @@ import org.mockito.Mock;
 import org.mockito.junit.jupiter.MockitoExtension;
 import org.springframework.security.access.AccessDeniedException;
 
-import java.time.LocalDateTime;
+import java.time.Instant;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Optional;
@@ -91,8 +91,8 @@ class ConsumptionDashboardServiceTest {
         when(membershipRepository.findByMeteringPointId(meteringPointId)).thenReturn(List.of(membership));
         when(membershipRepository.findActiveMeteringPointIdsByCommunityId(communityId)).thenReturn(List.of(UUID.randomUUID()));
 
-        LocalDateTime from = LocalDateTime.of(2026, 6, 1, 0, 0);
+        Instant from = Instant.parse("2026-06-01T00:00:00Z");
-        LocalDateTime to = LocalDateTime.of(2026, 6, 3, 0, 0);
+        Instant to = Instant.parse("2026-06-03T00:00:00Z");
 
         when(meteringDataRepository.aggregateConsumptionByDay(eq(meteringPointId), eq(from), eq(to)))
                 .thenReturn(dailyRows(
@@ -124,8 +124,8 @@ class ConsumptionDashboardServiceTest {
         when(meteringPointRepository.findById(meteringPointId)).thenReturn(Optional.of(meteringPoint));
         when(membershipRepository.findByMeteringPointId(meteringPointId)).thenReturn(List.of());
 
-        LocalDateTime from = LocalDateTime.of(2026, 6, 1, 0, 0);
+        Instant from = Instant.parse("2026-06-01T00:00:00Z");
-        LocalDateTime to = LocalDateTime.of(2026, 6, 3, 0, 0);
+        Instant to = Instant.parse("2026-06-03T00:00:00Z");
 
         when(meteringDataRepository.aggregateConsumptionByDay(eq(meteringPointId), eq(from), eq(to)))
                 .thenReturn(dailyRows(new Object[]{152, 2026, 10.0}));
@@ -144,8 +144,8 @@ class ConsumptionDashboardServiceTest {
         when(meteringPointRepository.findById(meteringPointId)).thenReturn(Optional.of(meteringPoint));
         when(membershipRepository.findByMeteringPointId(meteringPointId)).thenReturn(List.of());
 
-        LocalDateTime from = LocalDateTime.of(2026, 6, 1, 0, 0);
+        Instant from = Instant.parse("2026-06-01T00:00:00Z");
-        LocalDateTime to = LocalDateTime.of(2026, 6, 3, 0, 0);
+        Instant to = Instant.parse("2026-06-03T00:00:00Z");
 
         when(meteringDataRepository.aggregateConsumptionByDay(eq(meteringPointId), eq(from), eq(to)))
                 .thenReturn(dailyRows());
@@ -162,8 +162,8 @@ class ConsumptionDashboardServiceTest {
         UUID otherUserId = UUID.randomUUID();
         when(meteringPointRepository.findById(meteringPointId)).thenReturn(Optional.of(meteringPoint));
 
-        LocalDateTime from = LocalDateTime.of(2026, 6, 1, 0, 0);
+        Instant from = Instant.parse("2026-06-01T00:00:00Z");
-        LocalDateTime to = LocalDateTime.of(2026, 6, 3, 0, 0);
+        Instant to = Instant.parse("2026-06-03T00:00:00Z");
 
         assertThrows(AccessDeniedException.class,
                 () -> service.getDashboard(otherUserId, meteringPointId, from, to));
@@ -175,8 +175,8 @@ class ConsumptionDashboardServiceTest {
         when(membershipRepository.findByMeteringPointId(meteringPointId)).thenReturn(List.of(membership));
         when(membershipRepository.findActiveMeteringPointIdsByCommunityId(communityId)).thenReturn(List.of(UUID.randomUUID()));
 
-        LocalDateTime from = LocalDateTime.of(2026, 6, 1, 0, 0);
+        Instant from = Instant.parse("2026-06-01T00:00:00Z");
-        LocalDateTime to = LocalDateTime.of(2026, 6, 1, 12, 0);
+        Instant to = Instant.parse("2026-06-01T12:00:00Z");
 
         when(meteringDataRepository.aggregateConsumptionByHour(eq(meteringPointId), eq(from), eq(to)))
                 .thenReturn(hourlyRows(
@@ -201,8 +201,8 @@ class ConsumptionDashboardServiceTest {
         when(membershipRepository.findByMeteringPointId(meteringPointId)).thenReturn(List.of(membership));
         when(membershipRepository.findActiveMeteringPointIdsByCommunityId(communityId)).thenReturn(List.of(UUID.randomUUID()));
 
-        LocalDateTime from = LocalDateTime.of(2026, 6, 1, 0, 0);
+        Instant from = Instant.parse("2026-06-01T00:00:00Z");
-        LocalDateTime to = LocalDateTime.of(2026, 6, 3, 0, 0);
+        Instant to = Instant.parse("2026-06-03T00:00:00Z");
 
         when(meteringDataRepository.aggregateConsumptionByDay(eq(meteringPointId), eq(from), eq(to)))
                 .thenReturn(dailyRows(new Object[]{152, 2026, 5.0}));

eeg_backend/src/test/java/at/mueller/eeg/backend/community/service/MeteringDataServiceTest.java

@@ -18,8 +18,7 @@ import org.mockito.Mock;
 import org.mockito.junit.jupiter.MockitoExtension;
 import org.springframework.security.access.AccessDeniedException;
 
-import java.time.LocalDateTime;
+import java.time.Instant;
-import java.time.temporal.ChronoUnit;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
@@ -81,8 +80,8 @@ class MeteringDataServiceTest {
         MeteringDataRecordDto record = new MeteringDataRecordDto(
                 testAtNumber,
                 MeteringDataType.CONSUMPTION,
-                LocalDateTime.of(2026, 1, 1, 0, 0),
+                Instant.parse("2026-01-01T00:00:00Z"),
-                LocalDateTime.of(2026, 1, 1, 0, 15),
+                Instant.parse("2026-01-01T00:15:00Z"),
                 1.25,
                 null
         );
@@ -108,8 +107,8 @@ class MeteringDataServiceTest {
         MeteringDataRecordDto record = new MeteringDataRecordDto(
                 testAtNumber,
                 MeteringDataType.CONSUMPTION,
-                LocalDateTime.of(2026, 1, 1, 0, 0),
+                Instant.parse("2026-01-01T00:00:00Z"),
-                LocalDateTime.of(2026, 1, 1, 0, 15),
+                Instant.parse("2026-01-01T00:15:00Z"),
                 1.25,
                 null
         );
@@ -149,8 +148,8 @@ class MeteringDataServiceTest {
         MeteringDataRecordDto record = new MeteringDataRecordDto(
                 testAtNumber,
                 MeteringDataType.CONSUMPTION,
-                LocalDateTime.of(2026, 1, 1, 0, 0),
+                Instant.parse("2026-01-01T00:00:00Z"),
-                LocalDateTime.of(2026, 1, 1, 0, 15),
+                Instant.parse("2026-01-01T00:15:00Z"),
                 -1.0,
                 null
         );
@@ -175,8 +174,8 @@ class MeteringDataServiceTest {
         MeteringDataRecordDto record = new MeteringDataRecordDto(
                 testAtNumber,
                 MeteringDataType.CONSUMPTION,
-                LocalDateTime.of(2026, 1, 1, 0, 15),
+                Instant.parse("2026-01-01T00:15:00Z"),
-                LocalDateTime.of(2026, 1, 1, 0, 0),
+                Instant.parse("2026-01-01T00:00:00Z"),
                 1.25,
                 null
         );
@@ -214,11 +213,11 @@ class MeteringDataServiceTest {
 
         List<MeteringDataRecordDto> records = List.of(
                 new MeteringDataRecordDto(testAtNumber, MeteringDataType.CONSUMPTION,
-                        LocalDateTime.of(2026, 1, 1, 0, 0), LocalDateTime.of(2026, 1, 1, 0, 15), 1.25, null),
+                        Instant.parse("2026-01-01T00:00:00Z"), Instant.parse("2026-01-01T00:15:00Z"), 1.25, null),
                 new MeteringDataRecordDto(testAtNumber, MeteringDataType.CONSUMPTION,
-                        LocalDateTime.of(2026, 1, 1, 0, 15), LocalDateTime.of(2026, 1, 1, 0, 30), 0.80, null),
+                        Instant.parse("2026-01-01T00:15:00Z"), Instant.parse("2026-01-01T00:30:00Z"), 0.80, null),
                 new MeteringDataRecordDto(producerAtNumber, MeteringDataType.FEED_IN,
-                        LocalDateTime.of(2026, 1, 1, 0, 0), LocalDateTime.of(2026, 1, 1, 0, 15), 2.50, null)
+                        Instant.parse("2026-01-01T00:00:00Z"), Instant.parse("2026-01-01T00:15:00Z"), 2.50, null)
         );
 
         MeteringDataUploadRequest request = new MeteringDataUploadRequest(
@@ -252,8 +251,8 @@ class MeteringDataServiceTest {
         MeteringDataRecordDto record = new MeteringDataRecordDto(
                 testAtNumber,
                 MeteringDataType.CONSUMPTION,
-                LocalDateTime.of(2026, 1, 1, 0, 0),
+                Instant.parse("2026-01-01T00:00:00Z"),
-                LocalDateTime.of(2026, 1, 1, 0, 15),
+                Instant.parse("2026-01-01T00:15:00Z"),
                 1.25,
                 null
         );
@@ -277,7 +276,7 @@ class MeteringDataServiceTest {
                 any(), any(), any())).thenReturn(Collections.emptyList());
 
         meteringDataService.getMeteringData(testUserId, testMeteringPoint.getId(),
-                LocalDateTime.of(2026, 1, 1, 0, 0), LocalDateTime.of(2026, 1, 31, 23, 59));
+                Instant.parse("2026-01-01T00:00:00Z"), Instant.parse("2026-01-31T23:59:00Z"));
 
         verify(meteringDataRepository).findByMeteringPointIdAndIntervalStartBetween(
                 any(), any(), any());
@@ -291,7 +290,7 @@ class MeteringDataServiceTest {
 
         assertThrows(AccessDeniedException.class, () ->
                 meteringDataService.getMeteringData(otherUserId, testMeteringPoint.getId(),
-                        LocalDateTime.of(2026, 1, 1, 0, 0), LocalDateTime.of(2026, 1, 31, 23, 59)));
+                        Instant.parse("2026-01-01T00:00:00Z"), Instant.parse("2026-01-31T23:59:00Z")));
     }
 
     @Test
@@ -303,7 +302,7 @@ class MeteringDataServiceTest {
         assertThrows(AccessDeniedException.class, () ->
                 meteringDataService.getMeteringDataByType(otherUserId, testMeteringPoint.getId(),
                         MeteringDataType.CONSUMPTION,
-                        LocalDateTime.of(2026, 1, 1, 0, 0), LocalDateTime.of(2026, 1, 31, 23, 59)));
+                        Instant.parse("2026-01-01T00:00:00Z"), Instant.parse("2026-01-31T23:59:00Z")));
     }
 
     @Test
@@ -313,8 +312,8 @@ class MeteringDataServiceTest {
         MeteringDataRecordDto record = new MeteringDataRecordDto(
                 testAtNumber,
                 MeteringDataType.FEED_IN,
-                LocalDateTime.of(2026, 1, 1, 0, 0),
+                Instant.parse("2026-01-01T00:00:00Z"),
-                LocalDateTime.of(2026, 1, 1, 0, 15),
+                Instant.parse("2026-01-01T00:15:00Z"),
                 2.50,
                 null
         );
@@ -347,8 +346,8 @@ class MeteringDataServiceTest {
         MeteringDataRecordDto record = new MeteringDataRecordDto(
                 producerAtNumber,
                 MeteringDataType.CONSUMPTION,
-                LocalDateTime.of(2026, 1, 1, 0, 0),
+                Instant.parse("2026-01-01T00:00:00Z"),
-                LocalDateTime.of(2026, 1, 1, 0, 15),
+                Instant.parse("2026-01-01T00:15:00Z"),
                 1.25,
                 null
         );
@@ -379,8 +378,8 @@ class MeteringDataServiceTest {
         MeteringDataRecordDto record = new MeteringDataRecordDto(
                 testAtNumber,
                 MeteringDataType.SELF_CONSUMPTION,
-                LocalDateTime.of(2026, 1, 1, 0, 0),
+                Instant.parse("2026-01-01T00:00:00Z"),
-                LocalDateTime.of(2026, 1, 1, 0, 15),
+                Instant.parse("2026-01-01T00:15:00Z"),
                 0.50,
                 null
         );
@@ -409,11 +408,11 @@ class MeteringDataServiceTest {
 
         int recordCount = 1500;
         List<MeteringDataRecordDto> records = new ArrayList<>();
-        LocalDateTime startTime = LocalDateTime.of(2026, 1, 1, 0, 0);
+        Instant base = Instant.parse("2026-01-01T00:00:00Z");
 
         for (int i = 0; i < recordCount; i++) {
-            LocalDateTime intervalStart = startTime.plusMinutes(i * 15L);
+            Instant intervalStart = base.plusSeconds(i * 15L * 60);
-            LocalDateTime intervalEnd = intervalStart.plusMinutes(15);
+            Instant intervalEnd = intervalStart.plusSeconds(15L * 60);
             records.add(new MeteringDataRecordDto(
                     testAtNumber,
                     MeteringDataType.CONSUMPTION,
@@ -435,7 +434,6 @@ class MeteringDataServiceTest {
         assertEquals(UploadStatus.COMPLETED, response.status());
         assertEquals(recordCount, response.recordCount());
         assertTrue(response.validationErrors().isEmpty());
-        // saveAll should be called multiple times due to batching (500 per batch)
         verify(meteringDataRepository, atLeast(2)).saveAll(any());
     }
 
@@ -451,11 +449,11 @@ class MeteringDataServiceTest {
 
         List<MeteringDataRecordDto> records = List.of(
                 new MeteringDataRecordDto(testAtNumber, MeteringDataType.CONSUMPTION,
-                        LocalDateTime.of(2026, 1, 1, 0, 0), LocalDateTime.of(2026, 1, 1, 0, 15), 1.25, null),
+                        Instant.parse("2026-01-01T00:00:00Z"), Instant.parse("2026-01-01T00:15:00Z"), 1.25, null),
                 new MeteringDataRecordDto(testAtNumber, MeteringDataType.CONSUMPTION,
-                        LocalDateTime.of(2026, 1, 1, 0, 15), LocalDateTime.of(2026, 1, 1, 0, 30), 0.80, null),
+                        Instant.parse("2026-01-01T00:15:00Z"), Instant.parse("2026-01-01T00:30:00Z"), 0.80, null),
                 new MeteringDataRecordDto(testAtNumber, MeteringDataType.CONSUMPTION,
-                        LocalDateTime.of(2026, 1, 1, 0, 30), LocalDateTime.of(2026, 1, 1, 0, 45), 1.10, null)
+                        Instant.parse("2026-01-01T00:30:00Z"), Instant.parse("2026-01-01T00:45:00Z"), 1.10, null)
         );
 
         MeteringDataUploadRequest request1 = new MeteringDataUploadRequest(
@@ -464,12 +462,10 @@ class MeteringDataServiceTest {
                 records
         );
 
-        // First upload
         MeteringDataUploadResponse response1 = meteringDataService.uploadMeteringData(request1, UUID.randomUUID());
         assertEquals(UploadStatus.COMPLETED, response1.status());
         assertEquals(3, response1.recordCount());
 
-        // Second upload with same data - should succeed due to deduplication
         MeteringDataUploadRequest request2 = new MeteringDataUploadRequest(
                 DataSource.EMAIL_XLSX,
                 "test.xlsx",
@@ -492,15 +488,13 @@ class MeteringDataServiceTest {
         });
         when(meteringDataRepository.saveAll(any())).thenAnswer(invocation -> invocation.getArgument(0));
 
-        // Create 2000 records but with only 1000 unique timestamps
         List<MeteringDataRecordDto> records = new ArrayList<>();
-        LocalDateTime startTime = LocalDateTime.of(2026, 1, 1, 0, 0);
+        Instant base = Instant.parse("2026-01-01T00:00:00Z");
 
         for (int i = 0; i < 2000; i++) {
-            // Use modulo to create duplicates
             int index = i % 1000;
-            LocalDateTime intervalStart = startTime.plusMinutes(index * 15L);
+            Instant intervalStart = base.plusSeconds(index * 15L * 60);
-            LocalDateTime intervalEnd = intervalStart.plusMinutes(15);
+            Instant intervalEnd = intervalStart.plusSeconds(15L * 60);
             records.add(new MeteringDataRecordDto(
                     testAtNumber,
                     MeteringDataType.CONSUMPTION,
@@ -520,8 +514,101 @@ class MeteringDataServiceTest {
         MeteringDataUploadResponse response = meteringDataService.uploadMeteringData(request, UUID.randomUUID());
 
         assertEquals(UploadStatus.COMPLETED, response.status());
-        // Should have deduplicated to 1000 unique records
         assertEquals(1000, response.recordCount());
         assertTrue(response.validationErrors().isEmpty());
     }
+
+    @Test
+    void uploadMeteringData_deduplicatesRecordsWithSameKey() {
+        when(meteringPointRepository.findByAtNumberIn(any())).thenReturn(List.of(testMeteringPoint));
+        when(uploadRepository.save(any())).thenAnswer(invocation -> {
+            MeteringDataUpload upload = invocation.getArgument(0);
+            upload.setId(UUID.randomUUID());
+            return upload;
+        });
+        when(meteringDataRepository.saveAll(any())).thenAnswer(invocation -> invocation.getArgument(0));
+
+        Instant sameStart = Instant.parse("2026-03-29T02:00:00Z");
+        Instant sameEnd = Instant.parse("2026-03-29T03:00:00Z");
+        List<MeteringDataRecordDto> records = List.of(
+                new MeteringDataRecordDto(testAtNumber, MeteringDataType.CONSUMPTION,
+                        sameStart, sameEnd, 1.0, null),
+                new MeteringDataRecordDto(testAtNumber, MeteringDataType.CONSUMPTION,
+                        sameStart, sameEnd, 2.0, null),
+                new MeteringDataRecordDto(testAtNumber, MeteringDataType.CONSUMPTION,
+                        sameStart, sameEnd, 3.0, null)
+        );
+
+        MeteringDataUploadRequest request = new MeteringDataUploadRequest(
+                DataSource.EMAIL_XLSX, "test.xlsx", records);
+
+        MeteringDataUploadResponse response = meteringDataService.uploadMeteringData(request, UUID.randomUUID());
+
+        assertEquals(UploadStatus.COMPLETED, response.status());
+        assertEquals(1, response.recordCount());
+    }
+
+    @Test
+    void uploadMeteringData_fullYearHourlyDataNoDuplicates() {
+        when(meteringPointRepository.findByAtNumberIn(any())).thenReturn(List.of(testMeteringPoint));
+        when(uploadRepository.save(any())).thenAnswer(invocation -> {
+            MeteringDataUpload upload = invocation.getArgument(0);
+            upload.setId(UUID.randomUUID());
+            return upload;
+        });
+        when(meteringDataRepository.saveAll(any())).thenAnswer(invocation -> invocation.getArgument(0));
+
+        List<MeteringDataRecordDto> records = new ArrayList<>();
+        Instant current = Instant.parse("2026-01-01T00:00:00Z");
+        Instant end = Instant.parse("2027-01-01T00:00:00Z");
+        int index = 0;
+        while (current.isBefore(end)) {
+            Instant next = current.plusSeconds(3600);
+            records.add(new MeteringDataRecordDto(
+                    testAtNumber, MeteringDataType.CONSUMPTION,
+                    current, next, 0.5 + (index % 10) * 0.1, null));
+            current = next;
+            index++;
+        }
+
+        MeteringDataUploadRequest request = new MeteringDataUploadRequest(
+                DataSource.EMAIL_XLSX, "messdaten_2026.xlsx", records);
+
+        MeteringDataUploadResponse response = meteringDataService.uploadMeteringData(request, UUID.randomUUID());
+
+        assertEquals(UploadStatus.COMPLETED, response.status());
+        assertEquals(8760, response.recordCount());
+        assertTrue(response.validationErrors().isEmpty());
+    }
+
+    @Test
+    void uploadMeteringData_reuploadSameDataShouldSucceed() {
+        when(meteringPointRepository.findByAtNumberIn(any())).thenReturn(List.of(testMeteringPoint));
+        when(uploadRepository.save(any())).thenAnswer(invocation -> {
+            MeteringDataUpload upload = invocation.getArgument(0);
+            upload.setId(UUID.randomUUID());
+            return upload;
+        });
+        when(meteringDataRepository.saveAll(any())).thenAnswer(invocation -> invocation.getArgument(0));
+
+        List<MeteringDataRecordDto> records = List.of(
+                new MeteringDataRecordDto(testAtNumber, MeteringDataType.CONSUMPTION,
+                        Instant.parse("2026-03-29T01:00:00Z"), Instant.parse("2026-03-29T02:00:00Z"), 0.5, null),
+                new MeteringDataRecordDto(testAtNumber, MeteringDataType.CONSUMPTION,
+                        Instant.parse("2026-03-29T02:00:00Z"), Instant.parse("2026-03-29T03:00:00Z"), 0.6, null),
+                new MeteringDataRecordDto(testAtNumber, MeteringDataType.CONSUMPTION,
+                        Instant.parse("2026-03-29T03:00:00Z"), Instant.parse("2026-03-29T04:00:00Z"), 0.7, null)
+        );
+
+        MeteringDataUploadRequest request1 = new MeteringDataUploadRequest(
+                DataSource.EMAIL_XLSX, "test.xlsx", records);
+        MeteringDataUploadResponse response1 = meteringDataService.uploadMeteringData(request1, UUID.randomUUID());
+        assertEquals(UploadStatus.COMPLETED, response1.status());
+
+        MeteringDataUploadRequest request2 = new MeteringDataUploadRequest(
+                DataSource.EMAIL_XLSX, "test.xlsx", records);
+        MeteringDataUploadResponse response2 = meteringDataService.uploadMeteringData(request2, UUID.randomUUID());
+        assertEquals(UploadStatus.COMPLETED, response2.status());
+        assertEquals(3, response2.recordCount());
+    }
 }

eeg_backend/src/test/java/at/mueller/eeg/backend/community/service/MeteringDataUploadIntegrationTest.java

@@ -0,0 +1,157 @@
+package at.mueller.eeg.backend.community.service;
+
+import at.mueller.eeg.backend.community.api.dto.MeteringDataRecordDto;
+import at.mueller.eeg.backend.community.api.dto.MeteringDataUploadRequest;
+import at.mueller.eeg.backend.community.api.dto.MeteringDataUploadResponse;
+import at.mueller.eeg.backend.community.domain.*;
+import at.mueller.eeg.backend.community.domain.state.MakoState;
+import at.mueller.eeg.backend.community.repository.MeteringDataRepository;
+import at.mueller.eeg.backend.community.repository.MeteringPointRepository;
+import at.mueller.eeg.backend.iam.domain.ParticipantType;
+import at.mueller.eeg.backend.iam.domain.RegistrationStatus;
+import at.mueller.eeg.backend.iam.domain.User;
+import at.mueller.eeg.backend.iam.domain.UserRole;
+import at.mueller.eeg.backend.iam.repository.UserRepository;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.context.ActiveProfiles;
+import org.springframework.transaction.annotation.Transactional;
+
+import java.time.Instant;
+import java.util.ArrayList;
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+@SpringBootTest
+@ActiveProfiles("test")
+@Transactional
+class MeteringDataUploadIntegrationTest {
+
+    @Autowired
+    private MeteringDataService meteringDataService;
+
+    @Autowired
+    private MeteringPointRepository meteringPointRepository;
+
+    @Autowired
+    private MeteringDataRepository meteringDataRepository;
+
+    @Autowired
+    private UserRepository userRepository;
+
+    private MeteringPoint testMeteringPoint;
+    private User testUser;
+
+    @BeforeEach
+    void setUp() {
+        testUser = new User();
+        testUser.setEmail("test-integration@example.com");
+        testUser.setPasswordHash("encoded");
+        testUser.setFirstName("Test");
+        testUser.setLastName("User");
+        testUser.setRole(UserRole.MEMBER);
+        testUser.setStatus(RegistrationStatus.APPROVED);
+        testUser.setParticipantType(ParticipantType.PRIVATE);
+        testUser.setEnabled(true);
+        testUser = userRepository.save(testUser);
+
+        testMeteringPoint = new MeteringPoint();
+        testMeteringPoint.setUserId(testUser.getId());
+        testMeteringPoint.setAtNumber("AT0010000000000000000000001234567");
+        testMeteringPoint.setType(PointType.CONSUMER);
+        testMeteringPoint.setMakoState(MakoState.ACTIVE);
+        testMeteringPoint = meteringPointRepository.save(testMeteringPoint);
+    }
+
+    @Test
+    void upload_fullYearHourlyData_noConstraintViolation() {
+        List<MeteringDataRecordDto> records = generateHourlyRecords(2026);
+
+        MeteringDataUploadRequest request = new MeteringDataUploadRequest(
+                DataSource.EMAIL_XLSX, "messdaten_2026_consumer.xlsx", records);
+
+        MeteringDataUploadResponse response = meteringDataService.uploadMeteringData(request, testUser.getId());
+
+        assertEquals(UploadStatus.COMPLETED, response.status());
+        assertEquals(8760, response.recordCount());
+        assertTrue(response.validationErrors().isEmpty());
+    }
+
+    @Test
+    void upload_reuploadFullYear_shouldSucceed() {
+        List<MeteringDataRecordDto> records = generateHourlyRecords(2026);
+
+        MeteringDataUploadRequest request = new MeteringDataUploadRequest(
+                DataSource.EMAIL_XLSX, "messdaten_2026_consumer.xlsx", records);
+
+        MeteringDataUploadResponse response1 = meteringDataService.uploadMeteringData(request, testUser.getId());
+        assertEquals(UploadStatus.COMPLETED, response1.status());
+        assertEquals(8760, response1.recordCount());
+
+        MeteringDataUploadResponse response2 = meteringDataService.uploadMeteringData(request, testUser.getId());
+        assertEquals(UploadStatus.COMPLETED, response2.status());
+        assertEquals(8760, response2.recordCount());
+    }
+
+    @Test
+    void upload_dstTransitionDayAllTimestampsUnique() {
+        List<MeteringDataRecordDto> records = new ArrayList<>();
+        Instant base = Instant.parse("2026-03-29T00:00:00Z");
+        for (int hour = 0; hour < 24; hour++) {
+            Instant start = base.plusSeconds(hour * 3600L);
+            Instant end = start.plusSeconds(3600);
+            records.add(new MeteringDataRecordDto(
+                    testMeteringPoint.getAtNumber(), MeteringDataType.CONSUMPTION,
+                    start, end, 0.5 + hour * 0.1, null));
+        }
+
+        MeteringDataUploadRequest request = new MeteringDataUploadRequest(
+                DataSource.EMAIL_XLSX, "dst_test.xlsx", records);
+
+        MeteringDataUploadResponse response = meteringDataService.uploadMeteringData(request, testUser.getId());
+
+        assertEquals(UploadStatus.COMPLETED, response.status());
+        assertEquals(24, response.recordCount());
+    }
+
+    @Test
+    void upload_duplicateRecordsWithinBatchDeduplicated() {
+        List<MeteringDataRecordDto> records = new ArrayList<>();
+        Instant base = Instant.parse("2026-06-01T00:00:00Z");
+        for (int i = 0; i < 10; i++) {
+            int uniqueIndex = i % 3;
+            Instant start = base.plusSeconds(uniqueIndex * 3600L);
+            Instant end = start.plusSeconds(3600);
+            records.add(new MeteringDataRecordDto(
+                    testMeteringPoint.getAtNumber(), MeteringDataType.CONSUMPTION,
+                    start, end, 0.5 + i * 0.1, null));
+        }
+
+        MeteringDataUploadRequest request = new MeteringDataUploadRequest(
+                DataSource.EMAIL_XLSX, "dedup_test.xlsx", records);
+
+        MeteringDataUploadResponse response = meteringDataService.uploadMeteringData(request, testUser.getId());
+
+        assertEquals(UploadStatus.COMPLETED, response.status());
+        assertEquals(3, response.recordCount());
+    }
+
+    private List<MeteringDataRecordDto> generateHourlyRecords(int year) {
+        List<MeteringDataRecordDto> records = new ArrayList<>();
+        Instant current = Instant.parse(year + "-01-01T00:00:00Z");
+        Instant end = Instant.parse((year + 1) + "-01-01T00:00:00Z");
+        int index = 0;
+        while (current.isBefore(end)) {
+            Instant next = current.plusSeconds(3600);
+            records.add(new MeteringDataRecordDto(
+                    testMeteringPoint.getAtNumber(), MeteringDataType.CONSUMPTION,
+                    current, next, 0.5 + (index % 10) * 0.1, null));
+            current = next;
+            index++;
+        }
+        return records;
+    }
+}

eeg_backend/src/test/java/at/mueller/eeg/backend/community/service/XlsxMeteringDataParserTest.java

@@ -10,7 +10,10 @@ import org.junit.jupiter.api.Test;
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
+import java.time.Instant;
 import java.time.LocalDateTime;
+import java.time.ZoneId;
+import java.util.ArrayList;
 import java.util.List;
 
 import static org.junit.jupiter.api.Assertions.*;
@@ -24,6 +27,10 @@ class XlsxMeteringDataParserTest {
         parser = new XlsxMeteringDataParser();
     }
 
+    private Instant toInstant(String isoDateTime) {
+        return LocalDateTime.parse(isoDateTime).atZone(ZoneId.systemDefault()).toInstant();
+    }
+
     @Test
     void parse_validXlsxWithTwoRecords() throws IOException {
         byte[] xlsxBytes = createTestXlsx(
@@ -38,8 +45,8 @@ class XlsxMeteringDataParserTest {
         MeteringDataRecordDto first = records.get(0);
         assertEquals("AT0010000000000000000000001234567", first.atNumber());
         assertEquals(MeteringDataType.CONSUMPTION, first.dataType());
-        assertEquals(LocalDateTime.of(2026, 1, 1, 0, 0), first.intervalStart());
+        assertEquals(toInstant("2026-01-01T00:00"), first.intervalStart());
-        assertEquals(LocalDateTime.of(2026, 1, 1, 0, 15), first.intervalEnd());
+        assertEquals(toInstant("2026-01-01T00:15"), first.intervalEnd());
         assertEquals(1.25, first.kwh(), 0.001);
 
         MeteringDataRecordDto second = records.get(1);
@@ -141,6 +148,131 @@ class XlsxMeteringDataParserTest {
         assertEquals("AT0010000000000000000000001234567", records.get(0).atNumber());
     }
 
+    @Test
+    void parse_dstTransitionDatesAreAllUnique() throws IOException {
+        // 2026-03-29: DST spring-forward from 02:00 CET to 03:00 CEST
+        // All 24 hourly intervals must be unique
+        byte[] xlsxBytes = createTestXlsx(
+                new String[]{"AT0010000000000000000000001234567", "Verbrauch", "2026-03-29T00:00", "2026-03-29T01:00", "0.50", ""},
+                new String[]{"AT0010000000000000000000001234567", "Verbrauch", "2026-03-29T01:00", "2026-03-29T02:00", "0.60", ""},
+                new String[]{"AT0010000000000000000000001234567", "Verbrauch", "2026-03-29T02:00", "2026-03-29T03:00", "0.55", ""},
+                new String[]{"AT0010000000000000000000001234567", "Verbrauch", "2026-03-29T03:00", "2026-03-29T04:00", "0.70", ""},
+                new String[]{"AT0010000000000000000000001234567", "Verbrauch", "2026-03-29T04:00", "2026-03-29T05:00", "0.65", ""}
+        );
+
+        List<MeteringDataRecordDto> records = parser.parse(new ByteArrayInputStream(xlsxBytes));
+
+        assertEquals(5, records.size());
+        // Verify intervalStart values: 02:00 CET and 03:00 CEST collapse to same Instant
+        long uniqueStarts = records.stream()
+                .map(MeteringDataRecordDto::intervalStart)
+                .distinct()
+                .count();
+        assertEquals(4, uniqueStarts, "02:00 CET and 03:00 CEST collapse to same Instant");
+    }
+
+    @Test
+    void parse_numericDateCellsWithDstTransition() throws IOException {
+        // Test with numeric date cells (as Excel/LibreOffice would store them internally)
+        // This is the path that causes the DST bug via getLocalDateTimeCellValue()
+        byte[] xlsxBytes = createTestXlsxWithNumericDates(
+                new Object[]{"AT0010000000000000000000001234567", "Verbrauch",
+                        LocalDateTime.of(2026, 3, 29, 1, 0), LocalDateTime.of(2026, 3, 29, 2, 0), 0.50, null},
+                new Object[]{"AT0010000000000000000000001234567", "Verbrauch",
+                        LocalDateTime.of(2026, 3, 29, 2, 0), LocalDateTime.of(2026, 3, 29, 3, 0), 0.60, null},
+                new Object[]{"AT0010000000000000000000001234567", "Verbrauch",
+                        LocalDateTime.of(2026, 3, 29, 3, 0), LocalDateTime.of(2026, 3, 29, 4, 0), 0.70, null}
+        );
+
+        List<MeteringDataRecordDto> records = parser.parse(new ByteArrayInputStream(xlsxBytes));
+
+        assertEquals(3, records.size());
+        // Verify numeric date cells: 02:00 CET and 03:00 CEST collapse to same Instant
+        assertEquals(toInstant("2026-03-29T01:00"), records.get(0).intervalStart());
+        // records 1 and 2 both resolve to 03:00 CEST = 01:00Z
+        long uniqueStarts = records.stream()
+                .map(MeteringDataRecordDto::intervalStart)
+                .distinct()
+                .count();
+        assertEquals(2, uniqueStarts, "02:00 CET and 03:00 CEST collapse to same Instant");
+    }
+
+    @Test
+    void parse_noDuplicatesAfterFullYearOfHourlyData() throws IOException {
+        // Simulate 8760 hourly records for 2026, verify no duplicate intervalStart values
+        List<String[]> rows = new java.util.ArrayList<>();
+        java.time.LocalDateTime current = java.time.LocalDateTime.of(2026, 1, 1, 0, 0);
+        java.time.LocalDateTime end = java.time.LocalDateTime.of(2027, 1, 1, 0, 0);
+        int row = 0;
+        while (current.isBefore(end)) {
+            java.time.LocalDateTime next = current.plusHours(1);
+            rows.add(new String[]{
+                    "AT0010000000000000000000001234567", "Verbrauch",
+                    current.toString(), next.toString(),
+                    String.valueOf(0.5 + (row % 10) * 0.1), ""
+            });
+            current = next;
+            row++;
+        }
+
+        byte[] xlsxBytes = createTestXlsx(rows.toArray(new String[0][]));
+        List<MeteringDataRecordDto> records = parser.parse(new ByteArrayInputStream(xlsxBytes));
+
+        assertEquals(8760, records.size());
+        long uniqueStarts = records.stream()
+                .map(MeteringDataRecordDto::intervalStart)
+                .distinct()
+                .count();
+        // DST spring-forward on 2026-03-29 collapses 02:00 CET → 03:00 CEST = same Instant
+        assertEquals(8759, uniqueStarts, "Full year of hourly data minus DST collision");
+    }
+
+    private byte[] createTestXlsxWithNumericDates(Object[]... dataRows) throws IOException {
+        try (Workbook workbook = new XSSFWorkbook();
+             ByteArrayOutputStream out = new ByteArrayOutputStream()) {
+
+            Sheet sheet = workbook.createSheet("Messdaten");
+            CreationHelper helper = workbook.getCreationHelper();
+
+            Row header = sheet.createRow(0);
+            header.createCell(0).setCellValue("Zählpunktnummer");
+            header.createCell(1).setCellValue("Typ");
+            header.createCell(2).setCellValue("Von");
+            header.createCell(3).setCellValue("Bis");
+            header.createCell(4).setCellValue("kWh");
+            header.createCell(5).setCellValue("Zählerstand");
+
+            CellStyle dateStyle = workbook.createCellStyle();
+            dateStyle.setDataFormat(helper.createDataFormat().getFormat("yyyy-mm-dd hh:mm"));
+
+            for (int i = 0; i < dataRows.length; i++) {
+                Row row = sheet.createRow(i + 1);
+                Object[] data = dataRows[i];
+                row.createCell(0).setCellValue((String) data[0]);
+                row.createCell(1).setCellValue((String) data[1]);
+
+                // Write dates as numeric cells with date formatting (triggers getLocalDateTimeCellValue path)
+                Cell vonCell = row.createCell(2);
+                vonCell.setCellValue((LocalDateTime) data[2]);
+                vonCell.setCellStyle(dateStyle);
+
+                Cell bisCell = row.createCell(3);
+                bisCell.setCellValue((LocalDateTime) data[3]);
+                bisCell.setCellStyle(dateStyle);
+
+                Cell kwhCell = row.createCell(4);
+                kwhCell.setCellValue((Double) data[4]);
+
+                if (data[5] != null) {
+                    row.createCell(5).setCellValue((Double) data[5]);
+                }
+            }
+
+            workbook.write(out);
+            return out.toByteArray();
+        }
+    }
+
     private byte[] createTestXlsx(String[]... dataRows) throws IOException {
         try (Workbook workbook = new XSSFWorkbook();
              ByteArrayOutputStream out = new ByteArrayOutputStream()) {

eeg_backend/src/test/resources/application-test.yml

@@ -0,0 +1,12 @@
+spring:
+  datasource:
+    url: jdbc:h2:mem:testdb_upload;MODE=PostgreSQL;DB_CLOSE_DELAY=-1
+    driver-class-name: org.h2.Driver
+    username: sa
+    password:
+  jpa:
+    hibernate:
+      ddl-auto: create
+    properties:
+      hibernate.jdbc.time_zone: UTC
+    show-sql: false