done

src/main/java/com/kalyshev/yan/computer/model/Computer.java

@@ -76,6 +76,7 @@ public class Computer {
         return "Computer{" +
                 "id=" + id +
                 ", modelName='" + modelName + '\'' +
+                ", serialNum='" + serialNum + '\'' +
                 '}';
     }
 }

src/main/java/com/kalyshev/yan/monitor/service/MonitorService.java

@@ -1,6 +1,9 @@
 package com.kalyshev.yan.monitor.service;
 
 import com.kalyshev.yan.computer.model.Computer;
+import jakarta.persistence.TypedQuery;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
 import org.springframework.util.StringUtils;
@@ -10,9 +13,11 @@ import jakarta.persistence.EntityManager;
 import jakarta.persistence.EntityNotFoundException;
 import jakarta.persistence.PersistenceContext;
 import java.util.List;
+import java.util.Objects;
 
 @Service
 public class MonitorService {
+    private static final Logger log = LoggerFactory.getLogger(MonitorService.class);
     @PersistenceContext
     private EntityManager em;
 
@@ -72,12 +77,9 @@ public class MonitorService {
 
     @Transactional
     public Computer getComputer(Long id) {
-        List<Computer> computers = em.createQuery("select s from Computer").getResultList();
-        for (int i = 0; i < computers.size(); i++){
-            if (computers.get(i).getMonitor().getId() == id) {
-                return computers.get(i);
-            }
-        }
-        return null;
+        Computer computer = em.createQuery("select s from Computer s where s.monitor.id = :id", Computer.class)
+                .setParameter("id", id)
+                .getSingleResult();
+        return computer;
     }
 }

src/test/java/com/kalyshev/yan/JpaComputerTests.java

@@ -43,7 +43,7 @@ public class JpaComputerTests {
         final Computer computer = computerService.addComputer("Computer", "w7894572", monitor.getId(), cabinet.getId());
         log.info(computer.toString());
         Assertions.assertNotNull(computer.getId());
-        Assertions.assertNull(computer.getCabinet());
+        Assertions.assertEquals(cabinet, computer.getCabinet());
     }
     @Test
     void testComputerDelete() {

src/test/java/com/kalyshev/yan/JpaMonitorTests.java

@@ -73,6 +73,7 @@ public class JpaMonitorTests {
         computerService.deleteAllComputers();
         Monitor monitor = monitorService.addMonitor("Asus");
         Computer computer = computerService.addComputer("Model", "6sfv4", monitor.getId(), null);
+        log.info(computer.toString());
         Computer fetchedComputer = monitorService.getComputer(monitor.getId());
         Assertions.assertEquals(computer, fetchedComputer);
     }