使用SQLite处理POJO的DAO创建更好的模式 [英] Better pattern to handle DAO creation for POJO using SQLite

问题描述

我正在使用使用 SQLCipher ， Android的 ORMLite 的Android应用程序，以处理使用SQLite和 Jackson 存储的POJO进行解析

I'm working on an Android App that use SQLCipher, ORMLite for Android to handle to POJO storing with SQLite and Jackson for parsing.

我想知道是否会有更好的模式，我正在使用（由 stayforit ）获取与给定的Entity类对应的DAO。我有超过30个Entity类，我不断添加一些时间，每次，我必须创建一个与前一个类似的DAO类。我如何推广使用泛型类？

I'm wondering if there would be a better pattern that the one i'm using (Recommended by stayforit) to get the DAO corresponding to the Entity class given. I have over 30 Entity class and I keep adding some over the time and each time, I have to create a DAO class that looks exactly the same as the previous one. How could I generalize using a generic class?

这是我的DbManager类：

Here is my DbManager class:

public class DbManager {
    private static DbManager instance;
    private CipherDbHelper dbHelper;
    private SecureSharedPreferences settings;

    private DbManager() {

    }

    private DbManager(Context context, String password) {
        SQLiteDatabase.loadLibs(context);
        dbHelper = new CipherDbHelper(context, password);
    }

    public static void init(Context context, String password) {
        instance = new DbManager(context, password);
    }

    public static DbManager getInstance() {
        if (instance == null) {
            Log.e("DbManager", "DbManager is null");
        }
        return instance;
    }

    public <D extends Dao<T, String>, T> D getDAO(Class<T> clz) throws SQLException {
        return dbHelper.getDao(clz);
    }
}

这是一个我需要的经常性DAO类的例子生成每次我在项目中添加POJO实体时：

Here is an example of a recurrent DAO class I need to generate each time I add a POJO entity to my project:

public class CategoriesDAO extends BaseDAO<EntityCategories> {
    private static CategoriesDAO instance;

    private CategoriesDAO() {
    }

    public synchronized static CategoriesDAO getInstance() {
        if (instance == null) {
            instance = new CategoriesDAO();
        }
        return instance;
    }

    @Override
    public Dao<EntityCategories, String> getDAO() throws SQLException, java.sql.SQLException {
        return DbManager.getInstance().getDAO(EntityCategories.class);
    }
}

这是我如何在一个活动中使用它： / p>

Here is how I use it in an Activity:

CategoriesDAO.getInstance().addOrUpdate(categories);

推荐答案

您可以将POJO daos的实例存储在在BaseDao本身或子类中映射，然后使用未经检查的转换来提取它。

You could store the instances of your POJO daos in a map either inside your BaseDao itself or in a subclass and then use an unchecked cast to extract it out.

public class GenericDao<T> extends BaseDao<T>  {

  private static class InstanceHolder {
      static final Map<Class<?>, GenericDao<?>> INSTANCES = new HashMap<>();
  }

  public static synchronized <T> GenericDao<T> getInstance(Class<T> clazz) {
      GenericDao<T> dao = (GenericDao<T>)InstanceHolder.INSTANCES.get(clazz);
      if (dao == null) {
        dao = new GenericDao<T>();
        InstanceHolder.INSTANCES.put(clazz, dao);
      }
      return dao;
  }

  private GenericDao() {
  }
}

然后

    GenericDao<EntityCategories> foo = GenericDao.getInstance(EntityCategories.class);
    foo.addOrUpdate(....);

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