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正しい情報を選択するカーソルを取得するためにデータベースクエリを作成する方法を理解するのに苦労しています。

私のデータベースは次のように構成されています: http://i.stack.imgur.com/vPaoD.png (担当者がいないため画像を埋め込むことができません)

Feed は user と多対多の関係を持ち、 Item は user と 1 対多の関係を持ちます。

getUsers(Feed feed) というメソッドを使用して、特定のフィードにあるすべてのユーザーまたはアイテムを返すメソッドを作成したいと考えています。

私のデータベース コードは次のとおりです。 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;
}

}

クエリを「動的」にする方法に関する情報を Web で検索しようとしましたが、何も見つかりませんでした。:/

Cursor c = db.rawQuery("SELECT * FROM Item WHERE userID = (FeedUser テーブルからすべてのユーザーを選択する引数)");

そのようなクエリを作成する方法に関する役立つリンクを知っている人はいますか?

よろしくラワ

4

1 に答える 1

2

次のようなクエリを使用できます。

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

ただし、結合の方が効率的です。

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