Question

我有一个sqlite数据库，它与我的应用程序捆绑在一起作为资产，在我的应用程序首次启动时，数据库将被复制到具有以下代码的设备。

public class DataBaseHelper extends SQLiteOpenHelper {

    // The Android's default system path of your application database.
    private static String DB_PATH = "/data/data/my.apps.namespace/databases/";

    private static String DB_NAME = "DB.sqlite";

    private SQLiteDatabase myDataBase;

    private final Context myContext;

    public DataBaseHelper(Context context) {

        super(context, DB_NAME, null, 1);
        this.myContext = context;
    }

    /**
     * Creates a empty database on the system and rewrites it with your own
     * database.
     * */
    public void createDataBase() throws IOException {

        boolean dbExist = checkDataBase();

        if (dbExist) {
            // do nothing - database already exist
        } else {

            // By calling this method and empty database will be created into
            // the default system path
            // of your application so we are gonna be able to overwrite that
            // database with our database.
            this.getReadableDatabase();

            try {

                copyDataBase();

            } catch (IOException e) {

                throw new Error("Error copying database");

            }
        }

    }

    /**
     * Check if the database already exist to avoid re-copying the file each
     * time you open the application.
     * 
     * @return true if it exists, false if it doesn't
     */
    private boolean checkDataBase() {

        SQLiteDatabase checkDB = null;

        try {
            String myPath = DB_PATH + DB_NAME;
            checkDB = SQLiteDatabase.openDatabase(myPath, null,
                    SQLiteDatabase.OPEN_READONLY);

        } catch (SQLiteException e) {

            // database does't exist yet.

        }

        if (checkDB != null) {

            checkDB.close();

        }

        return checkDB != null ? true : false;
    }

    /**
     * Copies your database from your local assets-folder to the just created
     * empty database in the system folder, from where it can be accessed and
     * handled. This is done by transfering bytestream.
     * */
    private void copyDataBase() throws IOException {

        // Open your local db as the input stream
        InputStream myInput = myContext.getAssets().open(DB_NAME);

        // Path to the just created empty db
        String outFileName = DB_PATH + DB_NAME;

        // Open the empty db as the output stream
        OutputStream myOutput = new FileOutputStream(outFileName);

        // transfer bytes from the inputfile to the outputfile
        byte[] buffer = new byte[1024];
        int length;
        while ((length = myInput.read(buffer)) > 0) {
            myOutput.write(buffer, 0, length);
        }

        // Close the streams
        myOutput.flush();
        myOutput.close();
        myInput.close();

    }

    public void openDataBase() throws SQLException {

        // Open the database
        String myPath = DB_PATH + DB_NAME;
        myDataBase = SQLiteDatabase.openDatabase(myPath, null,
                SQLiteDatabase.OPEN_READWRITE);

    }

    @Override
    public synchronized void close() {

        if (myDataBase != null)
            myDataBase.close();

        super.close();

    }

    @Override
    public void onCreate(SQLiteDatabase db) {

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }

    ....

}

这似乎运行良好，因为我可以访问数据库数据，例如使用方法：

public Category getCategory(int id) {
        openDataBase();
        Cursor cursor = myDataBase.rawQuery(
                "select * from categories where _id = " + id, null);
        cursor.moveToFirst();
        while (!cursor.isAfterLast()) {
            Category cat = cursorToCategory(cursor);
            return cat;
        }
        // make sure to close the cursor
        cursor.close();
        return null;
    }

但是当我想向数据库添加内容时，它似乎没有被添加，我有以下方法

public void addToWordBank(Word currentWord) {
        openDataBase();
        myDataBase.rawQuery("INSERT into wordBank(english) VALUES(?) ",
                new String[] { currentWord.english });
    }

然而，当我使用下面的方法检查时，它总是返回false，

public boolean wordBankHas(Word currentWord) {
        openDataBase();
        Cursor cursor = myDataBase.rawQuery(
                "select * from wordBank where english =? ",
                new String[] { currentWord.english });
        if (cursor.getCount() <= 0) {
            return false;
        }
        return true;
    }

与插入等相关的日志似乎没有任何错误。

Answer 1

您使用rawQuery()代替execSQL()。

rawQuery()仅适用于SELECT 查询 execSQL()用于命令（即：INSERT，UPDATE，DELETE，...）。

项目未添加到数据库中

1 个答案: