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我在弄清楚我应该如何进行数据库查询以使光标选择正确的信息时遇到了一些麻烦。

我的数据库结构如下：http: //i.stack.imgur.com/vPaoD.png（无法嵌入图像，因为缺少代表）

Feed 与 user 是多对多的关系，而 Item 与 user 是一对多的关系。

我想创建一个方法，该方法使用名为 getUsers(Feed feed) 的方法返回特定提要中的所有用户或项目。

我的数据库代码是： public class DatabaseHelper extends SQLiteOpenHelper {

// Database static variables
private static final int DATABASE_VERSION = 1;
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";
private static final String USER_COLUMN_USERID = "userid";
private static final String USER_COLUMN_IMGURL = "ProfileImageURL";
private 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_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_TEXT
            + " TEXT," + ITEM_COLUMN_TIMESTAMP + " TEXT,"
            + 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!
    }

    // db.close();
}

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());
    // 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_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.insert(TABLE_ITEM, null, temp);

    }
    db.setTransactionSuccessful();
    db.endTransaction();
    // db.close();
}

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() {
    SQLiteDatabase db = getWritableDatabase();
    db.delete(TABLE_ITEM, 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());
        db.insert(TABLE_USER, null, temp);
    }
    db.setTransactionSuccessful();
    db.endTransaction();
}

public Cursor getAllUsers() {

    Cursor c = db.query(TABLE_USER, new String[] { USER_COLUMN_ID,
            USER_COLUMN_USERNAME }, null, null, null, null, null);
    return c;
}

public Cursor getUsers(Feed feed) {

    return null;
}

}

我试图在网上搜索有关如何“动态”查询的信息，但没有找到任何东西。：/

我的猜测是：Cursor c = db.rawQuery("SELECT * FROM Item WHERE userID = (some argument to select all users from FeedUser table)");

任何人都知道有关如何进行此类查询的任何有用链接？

最好的问候拉瓦

4

1 回答 1

2

您可以使用这样的查询：

SELECT *
FROM Item
WHERE userID IN (SELECT userID
                 FROM FeedUser
                 WHERE feedID = ?)

但是加入会更有效：

SELECT Item.field1, Item.field2, ...
FROM Item JOIN FeedUser
  ON Item.userID = FeedUser.userID
于 2012-10-11T13:15:49.043 回答