Question

我的数据库出现了一些问题，一旦我尝试从数据库中获取某些内容或将某些内容写入数据库，我就会将其实施到我的应用中。我还发现导致崩溃的线路，但我真的不知道如何解决它。

以下是我的数据库代码+错误消息

public class DatabaseHelper extends SQLiteOpenHelper {

    // Logcat tag
    private static final String LOG = "DatabaseHelper";

    // Database Version
    private static final int DATABASE_VERSION = 1;

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

    // Table Names
    private static final String TABLE_DRIVE = "drive";
    private static final String TABLE_ROUTE = "route";
    private static final String TABLE_CAR = "car";
    private static final String TABLE_FUEL = "fuel";
    private static final String TABLE_FUELCALC = "fuelcalc";

    // Drive
    private static final String KEY_DRIVE_ID = "did";
    private static final String KEY_DRIVE_BEGIN = "begin";
    private static final String KEY_DRIVE_END = "end";
    private static final String KEY_DRIVE_CAR = "car";

    // Route
    private static final String KEY_ROUTE_ID = "rid";
    private static final String KEY_ROUTE_DATE = "date";
    private static final String KEY_ROUTE_LATITUDE = "latitude";
    private static final String KEY_ROUTE_LONGITUDE = "longitude";
    private static final String KEY_ROUTE_DRIVE = "drive";

    // Car
    private static final String KEY_CAR_ID = "cid";
    private static final String KEY_CAR_NAME = "name";
    private static final String KEY_CAR_MARQUE = "marque";
    private static final String KEY_CAR_FUEL = "fuel";

    // Fuel
    private static final String KEY_FUEL_ID = "fid";
    private static final String KEY_FUEL_FUEL = "fuel";


    // Table Create Statements
    // Drive table create statement
    private static final String CREATE_TABLE_DRIVE = "CREATE TABLE "
            + TABLE_DRIVE + "(" 
            + KEY_DRIVE_ID + " INTEGER PRIMARY KEY AUTOINCREMENT," 
            + KEY_DRIVE_BEGIN + " TEXT,"
            + KEY_DRIVE_END + " TEXT," 
            + KEY_DRIVE_CAR + " INTEGER," 
            + " FOREIGN KEY (" + KEY_DRIVE_CAR 
            + ") REFERENCES " + TABLE_CAR + " (" + KEY_CAR_ID + ")" + ");";

    // Route table create statement
    private static final String CREATE_TABLE_ROUTE = "CREATE TABLE "
            + TABLE_ROUTE + "(" 
            + KEY_ROUTE_ID + " INTEGER PRIMARY KEY AUTOINCREMENT," 
            + KEY_ROUTE_DATE + " TEXT," 
            + KEY_ROUTE_LATITUDE + " TEXT," 
            + KEY_ROUTE_LONGITUDE + " TEXT," 
            + KEY_ROUTE_ID + " INTEGER," 
            + " FOREIGN KEY (" + KEY_ROUTE_DRIVE 
            + ") REFERENCES " + TABLE_DRIVE + " (" + KEY_DRIVE_ID + ")" + ");";

    // Car table create statement
    private static final String CREATE_TABLE_CAR = "CREATE TABLE " 
            + TABLE_CAR + "(" 
            + KEY_CAR_ID + " INTEGER PRIMARY KEY AUTOINCREMENT,"
            + KEY_CAR_NAME + " TEXT," 
            + KEY_CAR_MARQUE + " TEXT,"
            + KEY_CAR_FUEL + " INTEGER," 
            + " FOREIGN KEY (" + KEY_CAR_FUEL
            + ") REFERENCES " + TABLE_FUEL + " (" + KEY_FUEL_ID + ")" + ");";

    // Fuel table create statement
    private static final String CREATE_TABLE_FUEL = "CREATE TABLE "
            + TABLE_FUEL + "(" + KEY_FUEL_ID
            + " INTEGER PRIMARY KEY AUTOINCREMENT," + KEY_FUEL_FUEL + " TEXT"
            + ");";

    // FuelCalc table create statement
    // TODO

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

    @Override
    public void onOpen(SQLiteDatabase db) {
        super.onOpen(db);
        if (!db.isReadOnly()) {
            // Enable foreign key constraints
            db.execSQL("PRAGMA foreign_keys=ON;");
        }
    }

    @Override
    public void onCreate(SQLiteDatabase db) {

        // creating required tables
        db.execSQL(CREATE_TABLE_FUEL);
        db.execSQL(CREATE_TABLE_CAR);
        db.execSQL(CREATE_TABLE_DRIVE); This one and the one the line below are the cause of the crashes i think
        db.execSQL(CREATE_TABLE_ROUTE);

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // on upgrade drop older tables
        db.execSQL("DROP TABLE IF EXISTS " + CREATE_TABLE_FUEL);
        db.execSQL("DROP TABLE IF EXISTS " + CREATE_TABLE_CAR);
        db.execSQL("DROP TABLE IF EXISTS " + CREATE_TABLE_DRIVE);
        db.execSQL("DROP TABLE IF EXISTS " + CREATE_TABLE_ROUTE);

        // create new tables
        onCreate(db);
    }


    // close database
    public void closeDB() {
        SQLiteDatabase db = this.getReadableDatabase();
        if (db != null && db.isOpen())
            db.close();
    }
}

错误日志，

01-23 13:12:33.530: E/SQLiteOpenHelper(880): Couldn't open routeLogBook for writing (will try read-only):
01-23 13:12:33.530: E/SQLiteOpenHelper(880): android.database.sqlite.SQLiteException: Can't downgrade database from version 2 to 1

Answer 1

android.database.sqlite.SQLiteException: Can't downgrade database from version 2 to 1

当您的代码尝试使用版本1打开数据库时，您的设备有一个版本为2的数据库文件。您不提供onDowngrade()回调，因此会抛出异常。

只需删除旧数据库即可创建新数据库。卸载应用程序将删除数据库文件。

无法打开数据库进行写入

1 个答案: