piki-logan

src/main/java/com/yourssu/entitymanager/EntityManager.java

@@ -0,0 +1,6 @@
+package com.yourssu.entitymanager;
+
+public interface EntityManager {
+    public void persist(Object entity);
+    public <T> T merge(T entity);
+}

src/main/java/com/yourssu/entitymanager/EntityManagerImpl.java

@@ -0,0 +1,65 @@
+package com.yourssu.entitymanager;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class EntityManagerImpl implements EntityManager {
+
+    private final Map<Long, User> persistenceContext = new HashMap<>();
+    private long sequence = 1L;
+
+    // id가 null일 때 호출 (비영속 → 영속)
+    @Override
+    public void persist(Object entity) {
+        if (!(entity instanceof User)) {
+            throw new IllegalArgumentException("일단은 User 엔티티만 지원합니다.");
+        }
+
+        User user = (User) entity;
+
+        if (user.getId() != null) {
+            throw new IllegalStateException("이미 ID가 존재하는 엔티티입니다. persist 불가.");
+        }
+
+        user.setId(sequence++);
+
+        persistenceContext.put(user.getId(), user);
+
+        System.out.println("[persist] 저장됨: " + user.getId() + ", " + user.getName());
+    }
+
+    // 이미 ID가 있는 객체일 때 (준영속 → 영속)
+    @Override
+    public <T> T merge(T entity) {
+        if (!(entity instanceof User)) {
+            throw new IllegalArgumentException("일단은 User 엔티티만 지원합니다.");
+        }
+
+        User detached = (User) entity;
+
+        if (detached.getId() == null) {
+            throw new IllegalStateException("ID가 없는 엔티티는 merge할 수 없습니다.");
+        }
+
+        User managed = persistenceContext.get(detached.getId());
+
+        if (managed == null) {
+            managed = new User();
+            managed.setId(detached.getId());
+            persistenceContext.put(managed.getId(), managed);
+        }
+        managed.setName(detached.getName());
+
+        System.out.println("[merge] 병합됨: " + managed.getId() + ", " + managed.getName());
+
+        return (T) managed;
+    }
+
+    public void printStore() {
+        System.out.println("== 현재 영속성 컨텍스트 상태 ==");
+        for (Map.Entry<Long, User> entry : persistenceContext.entrySet()) {
+            User u = entry.getValue();
+            System.out.println("id=" + u.getId() + ", name=" + u.getName());
+        }
+    }
+}

src/main/java/com/yourssu/entitymanager/Main.java

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+package com.yourssu.entitymanager;
+
+public class Main {
+    public static void main(String[] args) {
+
+        EntityManager em = new EntityManagerImpl();
+        UserRespository userRepository = new UserRespository(em);
+
+        User user1 = new User();
+        user1.setName("피키");
+
+        System.out.println("persist test");
+        userRepository.save(user1);
+
+        System.out.println("merge test");
+        User detachedUser = new User(user1.getId(), "이름 수정");
+        userRepository.save(detachedUser);
+
+        System.out.println("또 다른 유저 persist");
+        User user2 = new User();
+        user2.setName("로건");
+        userRepository.save(user2);
+
+        System.out.println("영속성 컨텍스트 전체 출력");
+        ((EntityManagerImpl) em).printStore();
+    }
+}

src/main/java/com/yourssu/entitymanager/User.java

@@ -0,0 +1,19 @@
+package com.yourssu.entitymanager;
+
+public class User {
+    private Long id;
+    private String name;
+
+    public User() {}
+
+    public User(Long id, String name) {
+        this.id = id;
+        this.name = name;
+    }
+
+    public Long getId() { return id; }
+    public void setId(Long id) { this.id = id; }
+
+    public String getName() { return name; }
+    public void setName(String name) { this.name = name; }
+}

src/main/java/com/yourssu/entitymanager/UserRespository.java

@@ -0,0 +1,19 @@
+package com.yourssu.entitymanager;
+
+public class UserRespository {
+
+    private final EntityManager entityManager;
+
+    public UserRespository(EntityManager entityManager) {
+        this.entityManager = entityManager;
+    }
+
+    public void save(User user) {
+        if (user.getId() == null) {
+            entityManager.persist(user);
+        } else {
+            entityManager.merge(user);
+        }
+    }
+
+}

src/test/java/com/yourssu/entitymanager/UserRespositoryTest.java

@@ -0,0 +1,8 @@
+package com.yourssu.entitymanager;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class UserRespositoryTest {
+
+
+}