Step1: EntityLoader 구현

src/main/java/persistence/entity/CustomJpaRepository.java

@@ -7,10 +7,12 @@ public CustomJpaRepository(EntityManager entityManager) {
  this.entityManager = entityManager;
  }
 
- public T save(T t) {
- if (entityManager.isDirty(t)) {
- entityManager.merge(t);
+ public T save(T entity) {
+ if (entityManager.isNew(entity)) {
+ entityManager.persist(entity);
+ } else if (entityManager.isDirty(entity)) {
+ entityManager.merge(entity);
  }
- return t;
+ return entity;
  }
 }

src/main/java/persistence/entity/EntityLoader.java

@@ -0,0 +1,49 @@
+package persistence.entity;
+
+import jdbc.RowMapper;
+import jdbc.exception.RowMapException;
+import persistence.sql.util.ColumnFields;
+import persistence.sql.util.ColumnName;
+
+import java.lang.reflect.Field;
+import java.sql.ResultSet;
+import java.sql.ResultSetMetaData;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+public class EntityLoader<T> implements RowMapper<T> {
+ private final Class<T> clazz;
+ private final Map<String, Field> fieldsByName;
+
+ public EntityLoader(Class<T> clazz) {
+ this.clazz = clazz;
+ this.fieldsByName = ColumnFields.forQuery(clazz)
+ .stream().collect(Collectors.toMap(
+ ColumnName::build,
+ field -> {
+ field.setAccessible(true);
+ return field;
+ }
+ ));
+ }
+
+ @Override
+ public T mapRow(ResultSet resultSet) {
+ try {
+ final T object = clazz.getDeclaredConstructor().newInstance();
+ final ResultSetMetaData metaData = resultSet.getMetaData();
+ final int columnCount = metaData.getColumnCount();
+ for (int i = 1; i <= columnCount; i++) {
+ fieldsByName.get(
+ metaData.getColumnLabel(i)
+ ).set(
+ object,
+ resultSet.getObject(metaData.getColumnName(i))
+ );
+ }
+ return object;
+ } catch (Exception e) {
+ throw new RowMapException(e);
+ }
+ }
+}

src/main/java/persistence/entity/EntityManager.java

@@ -14,4 +14,6 @@ public interface EntityManager {
  void detach(Object entity);
 
  boolean isDirty(Object entity);
+
+ boolean isNew(Object entity);
 }

src/main/java/persistence/entity/EntityManagerImpl.java

@@ -1,7 +1,6 @@
 package persistence.entity;
 
 import jdbc.JdbcTemplate;
-import jdbc.RowMapperImpl;
 import persistence.sql.dml.DmlBuilder;
 
 import java.util.List;
@@ -31,9 +30,9 @@ public <T> Optional<T> find(Class<T> clazz, Object id) {
 
  @Override
  public void persist(Object entity) {
- final String query = hasEntity(entity)
- ? dml.getUpdateQuery(entity)
- : dml.getInsertQuery(entity);
+ final String query = isNew(entity)
+ ? dml.getInsertQuery(entity)
+ : dml.getUpdateQuery(entity);
  jdbcTemplate.execute(query);
  context.addEntity(entity);
  context.getDatabaseSnapshot(
@@ -70,17 +69,25 @@ public void detach(Object entity) {
 
  @Override
  public boolean isDirty(Object entity) {
- return !hasEntity(entity) || !EntityHelper.equals(
+ return !EntityHelper.equals(
  entity,
  context.getCachedDatabaseSnapshot(new EntityKey<>(entity))
  );
  }
 
+ @Override
+ public boolean isNew(Object entity) {
+ return !find(
+ entity.getClass(),
+ new EntityKey(entity).getEntityId()
+ ).isPresent();
+ }
+
  private <T> Optional<T> findFromDB(EntityKey<T> key) {
  Class<T> clazz = key.getEntityClass();
  List<T> entities = jdbcTemplate.query(
  dml.getFindByIdQuery(clazz, key.getEntityId()),
- new RowMapperImpl<>(clazz)
+ new EntityLoader<>(clazz)
  );
  if (entities.isEmpty()) {
  return Optional.empty();
@@ -91,11 +98,4 @@ private <T> Optional<T> findFromDB(EntityKey<T> key) {
  new EntityKey<>(entity), entity
  ));
  }
-
- private boolean hasEntity(Object entity) {
- return find(
- entity.getClass(),
- new EntityKey(entity).getEntityId()
- ).isPresent();
- }
 }