realized function to get order items by order id

src/main/java/com/app/bookstore/controller/OrderController.java

@@ -4,8 +4,10 @@
 import com.app.bookstore.dto.order.OrderResponseDto;
 import com.app.bookstore.dto.order.UpdateOrderRequestDto;
 import com.app.bookstore.model.Order;
+import com.app.bookstore.model.OrderItem;
 import com.app.bookstore.model.User;
 import com.app.bookstore.service.order.OrderService;
+import com.app.bookstore.service.order.item.OrderItemService;
 import io.swagger.v3.oas.annotations.Operation;
 import io.swagger.v3.oas.annotations.tags.Tag;
 import java.util.List;
@@ -26,6 +28,7 @@
 @Tag(name = "Order management", description = "Endpoints for managing orders")
 public class OrderController {
     private final OrderService orderService;
+    private final OrderItemService orderItemService;
 
     @PreAuthorize("hasRole('ROLE_USER')")
     @PostMapping
@@ -57,8 +60,8 @@ public OrderResponseDto updateStatus(
             summary = "Get all items by order id",
             description = "Retrieve all OrderItems for a specific order"
     )
-    public Object getAllById(@PathVariable Long id) {
-        return null;
+    public List<OrderItem> getAllById(@PathVariable Long id) {
+        return orderItemService.getAllById(id);
     }
 
     @PreAuthorize("hasRole('ROLE_USER')")

src/main/java/com/app/bookstore/repository/order/item/OrderItemRepository.java

@@ -0,0 +1,15 @@
+package com.app.bookstore.repository.order.item;
+
+import com.app.bookstore.model.OrderItem;
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.Query;
+
+import java.util.List;
+
+public interface OrderItemRepository extends JpaRepository<OrderItem, Long> {
+    @Query("SELECT oi FROM OrderItem oi "
+            + "JOIN FETCH oi.order "
+            + "JOIN FETCH oi.book "
+            + "WHERE oi.order.id = :id")
+    List<OrderItem> findAllById(Long id);
+}

src/main/java/com/app/bookstore/service/order/OrderService.java

@@ -4,6 +4,7 @@
 import com.app.bookstore.dto.order.OrderResponseDto;
 import com.app.bookstore.dto.order.UpdateOrderRequestDto;
 import com.app.bookstore.model.Order;
+
 import java.util.List;
 
 public interface OrderService {

src/main/java/com/app/bookstore/service/order/OrderServiceImpl.java

@@ -6,15 +6,19 @@
 import com.app.bookstore.exception.EntityNotFoundException;
 import com.app.bookstore.mapper.OrderMapper;
 import com.app.bookstore.model.Order;
+import com.app.bookstore.model.OrderItem;
 import com.app.bookstore.repository.order.OrderRepository;
 import java.util.List;
+
+import com.app.bookstore.repository.order.item.OrderItemRepository;
 import lombok.RequiredArgsConstructor;
 import org.springframework.stereotype.Service;
 
 @Service
 @RequiredArgsConstructor
 public class OrderServiceImpl implements OrderService {
     private final OrderRepository orderRepository;
+    private final OrderItemRepository orderItemRepository;
     private final OrderMapper orderMapper;
 
     @Override

src/main/java/com/app/bookstore/service/order/item/OrderItemService.java

@@ -0,0 +1,10 @@
+package com.app.bookstore.service.order.item;
+
+import com.app.bookstore.model.OrderItem;
+
+import java.util.List;
+
+public interface OrderItemService {
+
+    List<OrderItem> getAllById(Long id);
+}

src/main/java/com/app/bookstore/service/order/item/OrderItemServiceImpl.java

@@ -0,0 +1,20 @@
+package com.app.bookstore.service.order.item;
+
+import com.app.bookstore.model.OrderItem;
+import com.app.bookstore.repository.order.OrderRepository;
+import com.app.bookstore.repository.order.item.OrderItemRepository;
+import lombok.RequiredArgsConstructor;
+import org.springframework.stereotype.Service;
+
+import java.util.List;
+
+@Service
+@RequiredArgsConstructor
+public class OrderItemServiceImpl implements OrderItemService {
+    private final OrderItemRepository orderItemRepository;
+
+    @Override
+    public List<OrderItem> getAllById(Long id) {
+        return orderItemRepository.findAllById(id);
+    }
+}