java - 域类中的 ForeignCollection 初始化

Question

我有一个具有多对多关系的域对象。Menu可以有很多Categories，Category也可以有很多Menus。Menu负责Categories。

我为我的应用程序进行了相当分层的设计，域类与DAO-s （我有一个特殊的同步类用于访问工厂和存储库类并保持关系同步）和应用程序层（我在那里使用服务，例如AddMenuService所有逻辑存在）。

例如我创建了一个Menu和Category对象。通过特殊的 appender 类将此类别添加到菜单中。然后我同步对象（验证，检查对象是否存在于数据库中或创建一个新对象，如果需要，调用其他同步类，比较不同的对象并保存或更新它们）。类别只能通过 MenuSyncro 添加。

Menu m1 = new Menu("Menu for vegetarians");
Category cat1 = new Category("Drinks");

m1.getAppender().addCategory(cat1);

MenuSyncro ms = new MenuSyncro();
ms.synchronize(menu1);

我知道我可以使用，但是有没有什么方法可以在类和类中Dao.getEmptyForeignCollection(String fieldName);初始化而无需先访问 DAO 对象，因为我不断收到异常，因为这些集合没有初始化？ForeginCollection<MenuCategory> categories;MenuForeignCollection<MenuCategory> menus;CategoryNullReference

课程

菜单类

@DatabaseTable(tableName = "MENUS")
public class Menu
{
   private final static String ID_FIELD_NAME = "ID";
   private final static String NAME_FIELD_NAME = "NAME";

   @DatabaseField(generatedId = true, columnName = ID_FIELD_NAME)
   private int id;

   @DatabaseField(columnName = NAME_FIELD_NAME, canBeNull = false, unique = true, useGetSet = true)
   private String name;

   @ForeignCollectionField(eager = false)
   private ForeignCollection<MenuCategory> categories;

   @ForeignCollectionField(eager = false)
   private ForeignCollection<LocationMenu> locations;

   private MenuAppender appender;

   public Menu()
   {
      // for ORMLite
   }

   public Menu(String name)
   {
      this.name = name;
   }

   public int getId() { return id; }
   public String getName() { return name; }
   public void setName(String name) { this.name = name; }

   public ArrayList<Category> getCategories()
   {
      ArrayList<Category> categoriesList = new ArrayList<Category>();

      if (categories != null)
         for (MenuCategory menuCategory : categories)
            categoriesList.add(menuCategory.getCategory());

      return categoriesList;
   }

   public ForeignCollection<LocationMenu> getLocations()
   {
      return locations;
   }

   public MenuAppender getAppender()
   {
      if (appender== null)
         appender= new MenuAppender(this);

      return appender;
   }
}

类别.class

@DatabaseTable(tableName = "CATEGORIES")
public class Category
{
   private final static String ID_FIELD_NAME = "ID";
   private final static String NAME_FIELD_NAME = "NAME";

   @DatabaseField(generatedId = true, columnName = ID_FIELD_NAME)
   private int id;

   @DatabaseField(columnName = NAME_FIELD_NAME, canBeNull = false, unique = true, useGetSet = true)
   private String name;

   @ForeignCollectionField(eager = false)
   private ForeignCollection<MenuCategory> menus;

   public Category()
   {
      // for ORMLite
   }

   public Category(String name)
   {
      this.name = name;
   }

   public int getId() { return id; }
   public String getName() { return name; }
   public void setName(String name) { this.name = name; }

   public ArrayList<Menu> getMenus()
   {
      ArrayList<Menu> menusList = new ArrayList<Menu>();

      if (menus != null)
         for (MenuCategory menuCategory : menus)
            menusList.add(menuCategory.getMenu());

      return menusList;
   }

}

MenuCategory.class

   @DatabaseTable(tableName = "MENUS_CATEGORIES")
   public class MenuCategory
   {
      private final static String ID_FIELD_NAME = "ID";
      private final static String MENUS_ID_FIELD_NAME = "MENUS_ID";
      private final static String CATEGORIES_ID_FIELD_NAME = "CATEGORIES_ID";

      @SuppressWarnings("unused")
      @DatabaseField(generatedId = true, columnName = ID_FIELD_NAME)
      private int id;

      @DatabaseField(foreign = true, columnName = MENUS_ID_FIELD_NAME, canBeNull = false, foreignAutoCreate = true, foreignAutoRefresh = true)
      private Menu menu;

      @DatabaseField(foreign = true, columnName = CATEGORIES_ID_FIELD_NAME, canBeNull = false, foreignAutoCreate = true, foreignAutoRefresh = true)
      private Category category;

      public MenuCategory()
      {
         // for ORMLite
      }

      public MenuCategory(Menu menu, Category category)
      {
         this.menu = menu;
         this.category = category;
      }

      public Menu getMenu()
      {
         return menu;
      }

      public void setMenu(Menu menu)
      {
         this.menu = menu;
      }

      public Category getCategory()
      {
         return category;
      }

      public void setCategory(Category category)
      {
         this.category = category;
      }
   }

预先感谢，邪恶的

Answer 1

只需调用<lazyCollection>.iterator()就足以正确初始化您的集合。