我正在创建一个具有这种结构的数据库（4 个表）：http: //i.stack.imgur.com/vPaoD.png（由于缺少代表而无法嵌入）
我担心的是这个类的增长速度很快，而且因为它变得如此之大，所以在它中工作不再那么简单了。无论如何我可以重构（=将它分成几个类）我的databaseHelper，使其更简单，更有条理，但仍然易于使用？
公共类 DatabaseHelper 扩展 SQLiteOpenHelper {
// Database static variables
private static final int DATABASE_VERSION = 2;
private static final String DATABASE_NAME = "feedlrDatabase";
// Declaring feed table
private static final String TABLE_FEED = "feed";
private static final String FEED_COLUMN_ID = "_id";
private static final String FEED_COLUMN_NAME = "name";
// Declaring feed-user bridge table
private static final String TABLE_FEEDUSER = "feeduser";
private static final String FEEDUSER_COLUMN_FEED_ID = "feed_ID";
private static final String FEEDUSER_COLUMN_USER_ID = "user_ID";
// Declaring user table
private static final String TABLE_USER = "user";
private static final String USER_COLUMN_ID = "_id";
public static final String USER_COLUMN_USERNAME = "username";
public static final String USER_COLUMN_USERID = "userid";
public static final String USER_COLUMN_IMGURL = "ProfileImageURL";
public static final String USER_COLUMN_SOURCE = "source";
// Declaring item table
private static final String TABLE_ITEM = "item";
public static final String ITEM_COLUMN_ID = "_id";
public static final String ITEM_COLUMN_ITEMID = "itemid";
public static final String ITEM_COLUMN_TEXT = "text";
private static final String ITEM_COLUMN_TIMESTAMP = "timestamp";
private static final String ITEM_COLUMN_TYPE = "type";
private static final String ITEM_COLUMN_URL = "URL";
private static final String ITEM_COLUMN_IMGURL = "imgURL";
private static final String ITEM_COLUMN_USER_ID = "user_ID";
private SQLiteDatabase db = this.getWritableDatabase();
public DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
public void onCreate(SQLiteDatabase database) {
// @formatter:off
// Creating feed table
database.execSQL("CREATE TABLE " + TABLE_FEED + "(" + FEED_COLUMN_ID
+ " INTEGER PRIMARY KEY AUTOINCREMENT," + FEED_COLUMN_NAME
+ " TEXT UNIQUE" + ")");
// Creating feed-user bridge table
database.execSQL("CREATE TABLE " + TABLE_FEEDUSER + "("
+ FEEDUSER_COLUMN_FEED_ID + " INT NOT NULL,"
+ FEEDUSER_COLUMN_USER_ID + " INT NOT NULL" + ")");
// Creating user table
// TODO Should username be the unique idenifier of a user?!
database.execSQL("CREATE TABLE " + TABLE_USER + "(" + USER_COLUMN_ID
+ " INTEGER PRIMARY KEY AUTOINCREMENT," + USER_COLUMN_USERNAME
+ " TEXT NOT NULL," + USER_COLUMN_USERID + " TEXT UNIQUE,"
+ USER_COLUMN_IMGURL + " TEXT," + USER_COLUMN_SOURCE
+ " TEXT NOT NULL" + ")");
// Creating item table
database.execSQL("CREATE TABLE " + TABLE_ITEM + "(" + ITEM_COLUMN_ID
+ " INTEGER PRIMARY KEY AUTOINCREMENT," + ITEM_COLUMN_ITEMID
+ " INT UNIQUE," + ITEM_COLUMN_TEXT + " TEXT,"
+ ITEM_COLUMN_TIMESTAMP + " DATETIME," + ITEM_COLUMN_TYPE
+ " TEXT," + ITEM_COLUMN_URL + " TEXT," + ITEM_COLUMN_IMGURL
+ " TEXT," + ITEM_COLUMN_USER_ID + " INT NOT NULL" + ")");
// @formatter:on
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// Temporarily drops all tables
db.execSQL("DROP TABLE IF EXISTS " + TABLE_FEED);
db.execSQL("DROP TABLE IF EXISTS " + TABLE_FEEDUSER);
db.execSQL("DROP TABLE IF EXISTS " + TABLE_USER);
db.execSQL("DROP TABLE IF EXISTS " + TABLE_ITEM);
onCreate(db);
}
public void addFeed(Feed feed) {
ContentValues temp = new ContentValues();
temp.put(FEED_COLUMN_NAME, feed.getTitle());
try {
db.insertOrThrow(TABLE_FEED, null, temp);
} catch (SQLiteConstraintException e) {
Log.d("ERROR", "Inserted feed is not UNIQUE!");
// TODO Apply listener to notify the user that the feed name already
// exists!
}
}
public void removeFeed(Feed feed) {
String title = feed.getTitle();
long id = getFeedID(feed);
removeFeedBridge(id);
db.delete(TABLE_FEED, FEED_COLUMN_NAME + "=?", new String[] { title });
}
public ArrayList<String> listFeeds() {
final ArrayList<String> feeds = new ArrayList<String>();
Cursor c = db.rawQuery("SELECT * FROM " + TABLE_FEED, null);
while (c.moveToNext()) {
String s = c.getString(1);
feeds.add(s);
}
c.close();
return feeds;
}
public long getFeedID(Feed feed) {
String feedTitle = feed.getTitle();
SQLiteDatabase db = this.getReadableDatabase();
Cursor c = db.query(TABLE_FEED, new String[] { FEED_COLUMN_ID },
FEED_COLUMN_NAME + "=?", new String[] { feedTitle }, null,
null, null);
c.moveToNext();
Long id = Long.parseLong(c.getString(0));
c.close();
return id;
}
public long getUserID(User user) {
long id = user.getId();
SQLiteDatabase db = this.getReadableDatabase();
Cursor c = db.query(TABLE_USER, new String[] { USER_COLUMN_ID },
USER_COLUMN_ID + "=?", new String[] { id + "" }, null, null,
null);
c.moveToNext();
Long id1 = Long.parseLong(c.getString(0));
c.close();
return id1;
}
public ArrayList<String> listUsers() {
final ArrayList<String> users = new ArrayList<String>();
Cursor c = db.rawQuery("SELECT * FROM " + TABLE_USER, null);
while (c.moveToNext()) {
String s = c.getString(1);
users.add(s);
}
return users;
}
public void addUserToFeed(User user, Feed feed) {
long FeedID = getFeedID(feed);
long UserID = addUser(user);
// Add bridge connection
if (UserID != -1) {
addFeedUserBridge(FeedID, UserID);
}
}
public long addUser(User user) {
// TODO Check if the user already exists!!
ContentValues temp = new ContentValues();
temp.put(USER_COLUMN_USERNAME, user.getUserName());
temp.put(USER_COLUMN_USERID, user.getId());
temp.put(USER_COLUMN_IMGURL, user.getProfileImageURL());
temp.put(USER_COLUMN_SOURCE, "Twitter");
// TODO implement source on user?
long userID = db.insert(TABLE_USER, null, temp);
return userID;
}
public void addFeedUserBridge(long feedID, long userID) {
ContentValues temp = new ContentValues();
temp.put(FEEDUSER_COLUMN_FEED_ID, feedID);
temp.put(FEEDUSER_COLUMN_USER_ID, userID);
db.insert(TABLE_FEEDUSER, null, temp);
}
public void removeUserFromFeed(Feed feed, User user) {
long feedID = getFeedID(feed);
long userID = getUserID(user);
removeFeedUserBridge(feedID, userID);
}
private void removeUser(User user) {
long id = user.getId();
db.delete(TABLE_USER, USER_COLUMN_ID + "=?", new String[] { id + "" });
}
private void removeFeedUserBridge(long feedID, long userID) {
db.delete(TABLE_FEEDUSER, FEEDUSER_COLUMN_FEED_ID + "=?" + " and "
+ FEEDUSER_COLUMN_USER_ID + "=?", new String[] { feedID + "",
userID + "" });
}
public ArrayList<String> listFeedUser() {
final ArrayList<String> feeduser = new ArrayList<String>();
Cursor c = db.rawQuery("SELECT * FROM " + TABLE_FEEDUSER, null);
while (c.moveToNext()) {
feeduser.add(c.getString(0) + " " + c.getString(1));
}
c.close();
return feeduser;
}
private void removeFeedBridge(Long id) {
db.delete(TABLE_FEEDUSER, FEEDUSER_COLUMN_FEED_ID + "=?",
new String[] { id + "" });
}
public void updateUser(long userID) {
// TODO implement this method
}
public void addListOfItems(List<? extends Item> itemList) {
db.beginTransaction();
for (Item i : itemList) {
ContentValues temp = new ContentValues();
temp.put(ITEM_COLUMN_ITEMID, i.getId());
temp.put(ITEM_COLUMN_TEXT, i.getText());
temp.put(ITEM_COLUMN_TIMESTAMP, i.getTimestamp());
temp.put(ITEM_COLUMN_TYPE, i.getText());
temp.put(ITEM_COLUMN_URL, i.getURL());
temp.put(ITEM_COLUMN_IMGURL, i.getIMGURL());
temp.put(ITEM_COLUMN_USER_ID, i.getUser().getId());
db.insertWithOnConflict(TABLE_ITEM, null, temp, SQLiteDatabase.CONFLICT_IGNORE);
}
db.setTransactionSuccessful();
db.endTransaction();
}
public List<User> getUsersInFeed(Feed feed) {
List<User> users = new ArrayList<User>();
Cursor c = db
.rawQuery("SELECT * FROM " + TABLE_USER + " WHERE "
+ USER_COLUMN_USERID + " IN (SELECT "
+ FEEDUSER_COLUMN_USER_ID + " FROM " + TABLE_FEEDUSER
+ " WHERE " + FEEDUSER_COLUMN_FEED_ID + " = "
+ getFeedID(feed) + ")", null);
c.moveToFirst();
while (!c.isAfterLast()) {
users.add(new User(c.getLong(c.getColumnIndex(USER_COLUMN_USERID)),
c.getString(c.getColumnIndex(USER_COLUMN_USERNAME))));
c.moveToNext();
}
return users;
}
public Cursor getAllItems() {
Cursor c = db.query(TABLE_ITEM, new String[] { ITEM_COLUMN_ID,
ITEM_COLUMN_TEXT, ITEM_COLUMN_TIMESTAMP, ITEM_COLUMN_TYPE,
ITEM_COLUMN_URL, ITEM_COLUMN_IMGURL, ITEM_COLUMN_USER_ID },
null, null, null, null, null);
// db.close();
return c;
}
public long getItemTableSize() {
SQLiteDatabase database = this.getReadableDatabase();
long l = DatabaseUtils.queryNumEntries(database, TABLE_ITEM);
// database.close();
return l;
}
public void clearItemTable() {
db.delete(TABLE_ITEM, null, null);
}
public void clearUserTable() {
db.delete(TABLE_USER, null, null);
}
public void clearFeeds() {
db.delete(TABLE_FEED, null, null);
db.delete(TABLE_FEEDUSER, null, null);
}
public void addUsers(List<? extends User> users) {
db.beginTransaction();
for (User u : users) {
ContentValues temp = new ContentValues();
temp.put(USER_COLUMN_USERNAME, u.getUserName());
temp.put(USER_COLUMN_USERID, u.getId());
temp.put(USER_COLUMN_SOURCE, u.getSource());
db.insertWithOnConflict(TABLE_USER, null, temp, SQLiteDatabase.CONFLICT_IGNORE);
}
db.setTransactionSuccessful();
db.endTransaction();
}
public Cursor getAllUsers() {
Cursor c = db.query(TABLE_USER, new String[] { USER_COLUMN_ID,
USER_COLUMN_USERNAME, USER_COLUMN_USERID }, null, null, null,
null, null);
return c;
}
public Cursor getItems(Feed feed) {
Cursor c = db.rawQuery("SELECT * FROM " + TABLE_ITEM
+ " WHERE " + ITEM_COLUMN_USER_ID
+ " IN (SELECT " + FEEDUSER_COLUMN_USER_ID
+ " FROM " + TABLE_FEEDUSER
+ " WHERE " + FEEDUSER_COLUMN_FEED_ID
+ " = " + getFeedID(feed)
+ ") ORDER BY " + ITEM_COLUMN_TIMESTAMP + " DESC", null);
return c;
}
}
最好的问候拉瓦