src/main/java/de/zendric/app/xpensely_server/model/Expense.java

@@ -1,6 +1,7 @@
 package de.zendric.app.xpensely_server.model;
 
 import java.time.LocalDate;
+import java.time.LocalDateTime;
 
 import com.fasterxml.jackson.annotation.JsonBackReference;
 
@@ -36,6 +37,7 @@ public class Expense {
     private Double otherPersonAmount;
     private String category;
     private LocalDate date;
+    private LocalDateTime lastModified;
 
     @ManyToOne
     @JoinColumn(name = "expense_list_id", nullable = false)

src/main/java/de/zendric/app/xpensely_server/model/ExpenseHistoryEntry.java

@@ -0,0 +1,52 @@
+package de.zendric.app.xpensely_server.model;
+
+import java.time.LocalDateTime;
+
+import jakarta.persistence.Column;
+import jakarta.persistence.Entity;
+import jakarta.persistence.EnumType;
+import jakarta.persistence.Enumerated;
+import jakarta.persistence.GeneratedValue;
+import jakarta.persistence.GenerationType;
+import jakarta.persistence.Id;
+import jakarta.persistence.Index;
+import jakarta.persistence.JoinColumn;
+import jakarta.persistence.ManyToOne;
+import jakarta.persistence.Table;
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+import lombok.Setter;
+
+@Getter
+@Setter
+@NoArgsConstructor
+@Entity
+@Table(name = "expense_history_entry", indexes = @Index(name = "idx_history_list_timestamp", columnList = "expense_list_id, timestamp DESC"))
+public class ExpenseHistoryEntry {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+
+    @ManyToOne
+    @JoinColumn(name = "expense_list_id", nullable = false)
+    private ExpenseList expenseList;
+
+    /** Plain column on purpose — no FK, so history survives expense deletion. */
+    private Long expenseId;
+
+    /** Denormalized so entries for deleted expenses still render. */
+    private String expenseTitle;
+
+    @ManyToOne
+    private AppUser actor;
+
+    @Enumerated(EnumType.STRING)
+    private HistoryEntryType type;
+
+    private LocalDateTime timestamp;
+
+    /** JSON array of FieldChange; null for CREATED/DELETED. */
+    @Column(columnDefinition = "TEXT")
+    private String changes;
+}

src/main/java/de/zendric/app/xpensely_server/model/FieldChange.java

@@ -0,0 +1,9 @@
+package de.zendric.app.xpensely_server.model;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+
+public record FieldChange(
+        String field,
+        @JsonProperty("old") String oldValue,
+        @JsonProperty("new") String newValue) {
+}

src/main/java/de/zendric/app/xpensely_server/model/HistoryEntryType.java

@@ -0,0 +1,5 @@
+package de.zendric.app.xpensely_server.model;
+
+public enum HistoryEntryType {
+    CREATED, UPDATED, DELETED
+}

src/main/java/de/zendric/app/xpensely_server/repo/ExpenseHistoryRepository.java

@@ -0,0 +1,18 @@
+package de.zendric.app.xpensely_server.repo;
+
+import java.util.List;
+
+import org.springframework.data.domain.Page;
+import org.springframework.data.domain.Pageable;
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.Query;
+
+import de.zendric.app.xpensely_server.model.ExpenseHistoryEntry;
+
+public interface ExpenseHistoryRepository extends JpaRepository<ExpenseHistoryEntry, Long> {
+
+    Page<ExpenseHistoryEntry> findByExpenseListIdOrderByTimestampDescIdDesc(Long expenseListId, Pageable pageable);
+
+    @Query("select h.expenseId from ExpenseHistoryEntry h")
+    List<Long> findAllExpenseIds();
+}

src/main/java/de/zendric/app/xpensely_server/repo/ExpenseRepository.java

@@ -10,4 +10,6 @@ import de.zendric.app.xpensely_server.model.Expense;
 @Repository
 public interface ExpenseRepository extends JpaRepository<Expense, Long> {
     List<Expense> findAllByOrderByDateAsc();
+
+    List<Expense> findByLastModifiedIsNull();
 }