ducks-emin commit

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

@@ -0,0 +1,14 @@
+package com.yourssu.jpa;
+
+public class EntityManager<T, ID> {
+    private final PersistenceContext<T, ID> persistenceContext = new PersistenceContext<>();
+
+    public T persist(ID id, T entity) {
+        persistenceContext.save(id, entity);
+        return entity;
+    }
+
+    public void merge() {
+        persistenceContext.merge();
+    }
+}

src/main/java/com/yourssu/jpa/PersistenceContext.java

@@ -0,0 +1,34 @@
+package com.yourssu.jpa;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class PersistenceContext<T, ID> {
+    private final Map<ID, T> entityMap = new HashMap<>();
+    private final Map<ID, T> snapshotMap = new HashMap<>();
+
+
+    public void merge() {
+        for (ID id : entityMap.keySet()) {
+            T instance = entityMap.get(id);
+            T original = snapshotMap.get(id);
+
+            if (original == null) {
+                System.out.println("DB에 저장되었습니다. " + instance);
+                RealDB.push(id, instance);
+                continue;
+            }
+
+            if (original.equals(instance)) {
+                continue;
+            }
+            System.out.println("DB에 저장되었습니다. " + instance);
+            RealDB.push(id, instance);
+        }
+    }
+
+    public void save(ID id, T instance) {
+        System.out.println("영속성 컨텍스트에 저장되었습니다. " + instance);
+        entityMap.put(id, instance);
+    }
+}

src/main/java/com/yourssu/jpa/RealDB.java

@@ -0,0 +1,13 @@
+package com.yourssu.jpa;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class RealDB {
+
+    private static final Map<Object, Object> db = new HashMap<>();
+
+    public static void push(Object key, Object instance) {
+        db.put(key, instance);
+    }
+}

src/main/java/com/yourssu/jpa/Repository.java

@@ -0,0 +1,13 @@
+package com.yourssu.jpa;
+
+public class Repository {
+    private final EntityManager<UserEntity, Long> entityManager;
+
+    public Repository(EntityManager<UserEntity, Long> entityManager) {
+        this.entityManager = entityManager;
+    }
+
+    public UserEntity save(UserEntity entity) {
+        return entityManager.persist(entity.getId(), entity);
+    }
+}

src/main/java/com/yourssu/jpa/UserEntity.java

@@ -0,0 +1,31 @@
+package com.yourssu.jpa;
+
+import java.util.Objects;
+
+public class UserEntity {
+    private final Long id;
+    private String name;
+    private String email;
+
+    public UserEntity(Long id, String name, String email) {
+        this.id = id;
+        this.name = name;
+        this.email = email;
+    }
+
+    public Long getId() {
+        return id;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (o == null || getClass() != o.getClass()) return false;
+        UserEntity that = (UserEntity) o;
+        return Objects.equals(id, that.id) && Objects.equals(name, that.name) && Objects.equals(email, that.email);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(id, name, email);
+    }
+}

src/test/java/com/yourssu/EntityManagerTest.java

@@ -0,0 +1,21 @@
+package com.yourssu;
+
+
+import com.yourssu.jpa.EntityManager;
+import com.yourssu.jpa.Repository;
+import com.yourssu.jpa.UserEntity;
+import org.junit.jupiter.api.Test;
+
+class EntityManagerTest {
+    @Test
+    void persist() {
+        EntityManager<UserEntity, Long> entityManager = new EntityManager<>();
+        Repository repository = new Repository(entityManager);
+        // repository save 하고
+        // merge하고
+
+        UserEntity userEntity = new UserEntity(1L, "test", "[email protected]");
+        repository.save(userEntity);
+        entityManager.merge();
+    }
+}