I'm working on an Android App that use SQLCipher, ORMLite for Android to handle to POJO storing with SQLite and Jackson for parsing.
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?
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);
}
}
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);
}
}
Here is how I use it in an Activity:
CategoriesDAO.getInstance().addOrUpdate(categories);
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() {
}
}
and then
GenericDao<EntityCategories> foo = GenericDao.getInstance(EntityCategories.class);
foo.addOrUpdate(....);
That's the way I like to use Ormlite DAO's:
CRUDOperator:
public interface CRUDOperator<T> {
void create(T obj);
void update(T obj);
void delete(T obj);
}
Repo:
public interface Repo<T> extends CRUDOperator<T>{
Optional<T> queryForId(Integer id);
ObservableList<T> queryForAll();
...
}
OrmliteRepo:
public class OrmliteRepo<T> implements Repo<T> {
protected Dao<T, Integer> dao;
protected OrmliteRepo(Dao<T, Integer> dao) {
this.dao = dao;
}
public ObservableList<T> queryForAll() throws SQLException {
List<T> results = dao.queryForAll();
return Validators.isNullOrEmpty(results) ? FXCollections.observableArrayList() : FXCollections.observableArrayList(results);
}
public Optional<T> queryForId(Integer id) throws SQLException {
T result = dao.queryForId(id);
return Optional.ofNullable(result);
}
@Override
public void create(T obj) throws SQLException {
dao.create(obj);
}
@Override
public void update(T obj) throws SQLException {
dao.update(obj);
}
@Override
public void delete(T obj) throws SQLException {
dao.delete(obj);
}
}
YourRepo:
public class YourRepo extends OrmliteRepo<YourModel> {
public YourRepo(Dao<YourModel, Integer> dao) {
super(dao);
}
}
RepoService:
public interface RepoService {
<T> Repo<T> get(Class<T> dataClass);
}
BaseRepoService:
public class BaseRepoService implements RepoService {
private RepoFactory repoFactory;
private Map<Class<?>, Repo<?>> repoCache;
public BaseRepoService(RepoFactory repoFactory) {
this.repoFactory = repoFactory;
repoCache = new HashMap<>();
}
@Override
public <T> Repo<T> get(Class<T> dataClass) {
@SuppressWarnings("unchecked")
Repo<T> repo = (Repo<T>) repoCache.get(dataClass);
if (repo == null) {
repo = createRepo(dataClass);
repoCache.put(dataClass, repo);
}
return repo;
}
private <T> Repo<T> createRepo(Class<T> dataClass) {
return repoFactory.createRepo(dataClass);
}
}
RepoFactory:
public interface RepoFactory {
public <T> Repo<T> createRepo(Class<T> dataClass);
}
OrmliteRepoFactory:
public class OrmliteRepoFactory implements RepoFactory {
private DbAccess dbAccess;
private final Map<Class<?>, Supplier<OrmliteRepo<?>>> suppliers;
public OrmliteRepoFactory(DbAccess dbAccess) {
this.dbAccess = dbAccess;
suppliers = new HashMap<>();
suppliers.put(YourModel.class, () -> new YourRepo(getDao(YourModel.class)));
}
private <T> Dao<T, Integer> getDao(Class<T> modelClass) {
return dbAccess.getDaoImplementation(modelClass);
}
@Override
@SuppressWarnings("unchecked")
public <T> OrmliteRepo<T> createRepo(Class<T> dataClass) {
return (OrmliteRepo<T>) suppliers.get(dataClass).get();
}
}
DbAccess:
public interface DbAccess {
<T, R> R getDaoImplemantation(Class<T> dataClass);
}
OrmliteDbAccess:
public class OrmliteDbAccess implements DbAccess{
@Override
public <T, R> R getDaoImplementation(Class<T> objectClass) {
R dao = null;
try {
dao = DaoManager.createDao(connectionSource, objectClass);
} catch (SQLException e) {
LOGGER.error("Error getting dao for class {}; {}", objectClass, e);
}
return dao;
}
}
Now all you need to do is add the suppliers for your repos to the repoFactory and make YourRepo.class extend OrmliteRepo.class. If I need some additional behaviour for a specific repo, I put it in that repo implementation.
When you have an instance of RepoService:
RepoService repoService = new BaseRepoService(ormliteRepoFactory);
you can access your repo like this:
Repo<YourModel> repo = repoService.get(YourModel.class);