changed made clearer

src/main/java/com/yusufsezer/App.java

@@ -8,6 +8,7 @@
 import com.yusufsezer.util.JPAUtils;
 import com.yusufsezer.util.JavaFXUtils;
 import jakarta.persistence.EntityManager;
+import java.util.List;
 import javafx.application.Application;
 import javafx.fxml.FXMLLoader;
 import javafx.scene.Scene;
@@ -56,7 +57,12 @@ public void init() throws Exception {
                     entityManager.persist(task);
                 }
             }
+
             entityManager.getTransaction().commit();
+
+            Category foundCategory = categoryService.find(1L);
+            List<Task> tasks = foundCategory.getTasks();
+            tasks.forEach(System.out::println);
         }
 
         @Override

src/main/java/com/yusufsezer/contract/DialogControllerBase.java

@@ -7,4 +7,5 @@ public interface DialogControllerBase<T> {
     public abstract T edit(T entity);
 
     public abstract void set(T entity);
+
 }

src/main/java/com/yusufsezer/controller/MainController.java

@@ -6,9 +6,12 @@
 import com.yusufsezer.controller.dialog.TaskDialogController;
 import com.yusufsezer.model.Category;
 import com.yusufsezer.model.Task;
+import com.yusufsezer.service.CategoryService;
+import com.yusufsezer.service.TaskService;
 import com.yusufsezer.util.DummyDataUtils;
 import com.yusufsezer.util.JPAUtils;
 import java.net.URL;
+import java.util.List;
 import java.util.Optional;
 import java.util.ResourceBundle;
 import javafx.collections.FXCollections;
@@ -80,7 +83,8 @@ public void initialize(URL url, ResourceBundle rb) {
     void onAddNewCategory(MouseEvent event) {
         Optional<Category> result = CategoryDialogController.createAddCategoryDialog();
         if (result.isPresent()) {
-            JPAUtils.getCategoryService().create(result.get());
+            CategoryService categoryService = JPAUtils.getCategoryService();
+            categoryService.create(result.get());
             loadCategories();
         }
     }
@@ -91,7 +95,8 @@ void onKeyTaskReleased(KeyEvent event) {
         if (isEnterPressed) {
             Optional<Task> result = TaskDialogController.createAddTaskDialog(quickAddTextField.getText());
             if (result.isPresent()) {
-                JPAUtils.getTaskService().create(result.get());
+                TaskService taskService = JPAUtils.getTaskService();
+                taskService.create(result.get());
             }
             quickAddTextField.clear();
         }
@@ -115,7 +120,8 @@ void onMouseEditPressed(MouseEvent event) {
         if (selectedTask != null) {
             Optional<Task> result = TaskDialogController.createEditTaskDialog(selectedTask);
             if (result.isPresent()) {
-                JPAUtils.getTaskService().edit(result.get());
+                TaskService taskService = JPAUtils.getTaskService();
+                taskService.edit(result.get());
             }
         }
     }
@@ -125,7 +131,8 @@ void onMouseRemovePressed(MouseEvent event) {
         Task selectedTask = taskListView.getSelectionModel().getSelectedItem();
         if (selectedTask != null) {
             selectedTask.setDeleted(true);
-            JPAUtils.getTaskService().edit(selectedTask);
+            TaskService taskService = JPAUtils.getTaskService();
+            taskService.edit(selectedTask);
             taskListView.getItems().remove(selectedTask);
             taskListView.getSelectionModel().selectFirst();
         }
@@ -141,7 +148,11 @@ void onShowAbout(MouseEvent event) {
     }
 
     void showCategoryTasks(Category category) {
-        taskListView.getItems().setAll(JPAUtils.getCategoryService().find(category.getId()).getTasks());
+        CategoryService categoryService = JPAUtils.getCategoryService();
+        Long categoryId = category.getId();
+        Category foundCategory = categoryService.find(categoryId);
+        List<Task> categoryTasks = foundCategory.getTasks();
+        taskListView.getItems().setAll(categoryTasks);
     }
 
     void showTaskContent(Task selectedTask) {
@@ -152,7 +163,9 @@ void showTaskContent(Task selectedTask) {
     }
 
     void loadCategories() {
-        categoryListView.getItems().setAll(JPAUtils.getCategoryService().findAll());
+        CategoryService categoryService = JPAUtils.getCategoryService();
+        List<Category> categories = categoryService.findAll();
+        categoryListView.getItems().setAll(categories);
     }
 
 }

src/main/java/com/yusufsezer/controller/custom/TaskCellController.java

@@ -39,4 +39,5 @@ protected void updateItem(Task task, boolean empty) {
             setGraphic(null);
         }
     }
+
 }

src/main/java/com/yusufsezer/controller/dialog/CategoryDialogController.java

@@ -43,8 +43,7 @@ public static Optional<Category> createAddCategoryDialog() {
         return dialog.showAndWait();
     }
 
-    public static Optional<Category>
-            createEditCategoryDialog(Category category) {
+    public static Optional<Category> createEditCategoryDialog(Category category) {
         String title = JavaFXUtils.getBundleMessage("dialog.categoryEditTitle");
         String headerText = JavaFXUtils.getBundleMessage("dialog.categoryEditHeaderText");
         String fxml = "category";

src/main/java/com/yusufsezer/model/Category.java

@@ -19,6 +19,7 @@ public class Category extends BaseEntity implements Serializable {
 
     private String color;
     private String name;
+
     @Lob
     @Column(length = 1000)
     private String description;

src/main/java/com/yusufsezer/model/Task.java

@@ -21,6 +21,7 @@ public enum Status {
 
     private Status status;
     private String name;
+
     @Lob
     @Column(length = 1000)
     private String description;

src/main/java/com/yusufsezer/util/DialogUtils.java

@@ -14,7 +14,8 @@ public static <T extends BaseEntity> Dialog<T> createCustomDialog(String title,
         Dialog<T> dialog = new Dialog<>();
         dialog.setTitle(title);
         dialog.setHeaderText(headerText);
-        dialog.getDialogPane().setContent(JavaFXUtils.<Node>loadCustomFXML(DIALOG_FOLDER, fxml, controller));
+        Node node = JavaFXUtils.<Node>loadCustomFXML(DIALOG_FOLDER, fxml, controller);
+        dialog.getDialogPane().setContent(node);
         dialog.getDialogPane().getButtonTypes().addAll(ButtonType.OK, ButtonType.CLOSE);
         return dialog;
     }

src/main/java/com/yusufsezer/util/JPAUtils.java

@@ -13,6 +13,8 @@ public class JPAUtils {
     private static final String PERSISTENCE_UNIT_NAME = "YSTodoFXPU";
     private static EntityManagerFactory entityManagerFactory;
     private static EntityManager entityManager;
+    private static CategoryService categoryService;
+    private static TaskService taskService;
 
     static {
         try {
@@ -31,11 +33,17 @@ public static EntityManager getEntityManager() {
     }
 
     public static CategoryService getCategoryService() {
-        return new CategoryService(getEntityManager());
+        if (categoryService == null) {
+            categoryService = new CategoryService(getEntityManager());
+        }
+        return categoryService;
     }
 
     public static TaskService getTaskService() {
-        return new TaskService(getEntityManager());
+        if (taskService == null) {
+            taskService = new TaskService(getEntityManager());
+        }
+        return taskService;
     }
 
 }