Android SQLite - 主键 - 插入表

Question

我正处于为我的 Android 应用程序创建数据库的最后阶段，但是，我似乎无法让我的主键递增。这是我设置它的代码，

public class DatabaseHandler extends SQLiteOpenHelper {

    // All Static variables
    // Database Version
    private static final int DATABASE_VERSION = 17;

    // Database Name
    private static final String DATABASE_NAME = "journeyManager";

    // Contacts table name
    public static final String TABLE_JOURNEY = "journey";

    // Contacts Table Columns names
    private static final String KEY_P = "key";
    private static final String KEY_ID = "id";
    private static final String KEY_DIST = "distance";
    private static final String KEY_MPG = "mpg";
    private static final String KEY_COST = "cost";

    public DatabaseHandler(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    // Creating Tables
    @Override
    public void onCreate(SQLiteDatabase db) {
        String CREATE_JOURNEY_TABLE = "CREATE TABLE " + TABLE_JOURNEY + "("
                + KEY_P + " INTEGER PRIMARY KEY," + KEY_ID + " TEXT," + KEY_DIST + " TEXT,"
                + KEY_MPG + " TEXT," + KEY_COST + " TEXT )";
        db.execSQL(CREATE_JOURNEY_TABLE);
    }

    // Upgrading database
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // Drop older table if existed
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_JOURNEY);

        // Create tables again
        onCreate(db);
    }

    /**
     * All CRUD(Create, Read, Update, Delete) Operations
     */

    // Adding new contact
    void addJourneyData(Journey journey) {
        SQLiteDatabase db = this.getWritableDatabase();

        ContentValues values = new ContentValues();
        values.put(KEY_P, journey.getpKey());
        values.put(KEY_ID, journey.getId());
        values.put(KEY_DIST, journey.getDistance()); // Contact Name
        values.put(KEY_MPG, journey.getMpg()); // Contact Phone
        values.put(KEY_COST, journey.getCost()); // Contact Phone

        // Inserting Row
        db.insert(TABLE_JOURNEY, null, values);
        db.close(); // Closing database connection
    }

    // Getting single contact
    Journey getJourney(int id) {
        SQLiteDatabase db = this.getReadableDatabase();

        Cursor cursor = db.query(TABLE_JOURNEY, new String[] { KEY_P + KEY_ID + 
                KEY_DIST, KEY_MPG, KEY_COST }, KEY_P + "=?",
                new String[] { String.valueOf(id) }, null, null, null, null);
        if (cursor != null)
            cursor.moveToFirst();

        Journey journey = new Journey();
        journey.setPkey(Integer.parseInt(cursor.getString(0)));
        journey.setId(String.valueOf(cursor.getString(1)));
        journey.setMpg(String.valueOf(cursor.getString(2)));
        journey.setDistance(String.valueOf(cursor.getString(3)));
        journey.setCost(String.valueOf(cursor.getString(4)));
        // return contact
        return journey;
    }

    // Getting All Contacts
    public List<Journey> getAllJourneys() {
        List<Journey> journeyList = new ArrayList<Journey>();
        // Select All Query
        String selectQuery = "SELECT  * FROM " + TABLE_JOURNEY;

        SQLiteDatabase db = this.getWritableDatabase();
        Cursor cursor = db.rawQuery(selectQuery, null);

        // looping through all rows and adding to list
        if (cursor.moveToFirst()) {
            do {
                Journey journey = new Journey();
                journey.setPkey(Integer.parseInt(cursor.getString(0)));
                journey.setId(String.valueOf(cursor.getString(1)));
                journey.setMpg(String.valueOf(cursor.getString(2)));
                journey.setDistance(String.valueOf(cursor.getString(3)));
                journey.setCost(String.valueOf(cursor.getString(4)));
                // Adding contact to list
                journeyList.add(journey);
            } while (cursor.moveToNext());
        }

        // return contact list
        return journeyList;
    } 
}

这是我通过另一个 Activity 的按钮将详细信息添加到数据库的地方，

db.addJourneyData(new Journey(1,timeStamp, distanceLabel, mpgAnswer, pplAnswer));

我到了要点，它将添加第一个，但从那时起它会说主键不是唯一的 - 因此它不会更新数据库。

此外，我希望数据按降序排列，为此，我使用 DESC，但我应该将其放置在何处？

如有任何帮助，我们将不胜感激

非常感谢，

Answer 1

要使数据库自动为您生成主键，只需不要自己指定即可。从插入代码中删除这一行:

values.put(KEY_P, journey.getpKey());

可以从insert()的返回值中获取生成的id .

Also, I want the data to be in descending order, to do this, I use DESC, but where shall I place this?

假设这适用于执行 rawQuery() 的 getAllJourneys()，只需在 SQL 中直接添加 ORDER BY:

String selectQuery = "SELECT  * FROM " + TABLE_JOURNEY + " ORDER BY " + KEY_P + " DESC";