SQLite 数据库查询 Android

Question

我在我的 Android 应用上查询 SQLite 数据库时遇到问题。我使用this tutorial 来设置我的数据库助手类。

我做了一个简单的查询函数：

public Cursor queryDB(String Query,String[] args){  

Cursor cursor = myDataBase.rawQuery(Query, args);

return cursor;

然后我这样称呼它：

 String[] testarg = {"Denver Bake"};
 myDataBase.getReadableDatabase();
 Cursor results = myDataBase.queryDB("SELECT * FROM Recipes WHERE r_name = ?", testarg);

我得到的错误是：

 E/AndroidRuntime(30483): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.dbtest/com.example.dbtest.MainActivity}: android.database.sqlite.SQLiteException: no such table: Recipes: , while compiling: SELECT * FROM Recipes WHERE r_name = ?

我知道Recipes 表确实存在于我的数据库中，因为它出现在本教程的SQLite 数据库浏览器中。我已经尝试了教程 cmets 中的一些建议，但我仍然遇到同样的错误，我不确定现在该怎么做。

先谢谢了。

这是我的创作

public void createDataBase() throws IOException{
    boolean dbExist = checkDataBase();
    if(dbExist){
            //do nothing - database already exist
    }else{

        this.getReadableDatabase();
        try {
            copyDataBase();
            } catch (IOException e) {

            throw new Error("Error copying database");
            }
    }
}

这是我的复制代码：

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();
}

最后，我的资产文件夹中确实有我的数据库。错误信息告诉我数据库中的表不存在。

Answer 1

您必须在浏览器中创建自己的 SQLite 数据库，并将此数据库复制到项目的 assets 文件夹中：

1. 在浏览器中创建数据库。
2. 复制数据库
3. 粘贴到您的资产文件夹中。
4. 创建一些扩展 SQLiteOpenHelper 类的 dbhelper 类，并将数据库从 assets 文件夹中复制出来，以便应用可以访问它：

public class DbHelper extends SQLiteOpenHelper {

    // The Android's default system path of your application database.
    private static String PACKAGENAME = "com.SVLL";
    private static String DB_PATH = "/data/data/" + PACKAGENAME + "/databases/";
    private static String DB_NAME = "SVLL.sqlite";

    private static final String TAG = "DbHelper";
    private SQLiteDatabase myDataBase;

    private final Context myContext;

    /**
     * Constructor Takes and keeps a reference of the passed context in order to
     * access to the application assets and resources.
     * 
     * @param context
     */
    public DbHelper(final 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 final void createDataBase() throws IOException {

        final boolean dbExist = checkDataBase();
        SQLiteDatabase db_Read = null;
        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.
            // 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.
            // db_Read = this.getReadableDatabase(DB_Internal);
            db_Read = this.getReadableDatabase();
            db_Read.close();

            copyDataBase();

        }
    }

    /**
     * Restore whole database without any data
     * 
     * @throws IOException
     */
    public final void RestoreDatabase() throws IOException {
        SQLiteDatabase db_Read = this.getReadableDatabase();
        db_Read.close();

        copyDataBase();
        Log.i(TAG, "Database REstored");
    }

    /**
     * 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() {
        final File dbFile = new File(DB_PATH + DB_NAME);
        return dbFile.exists();
    }

    /**
     * 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.
     * 
     * @throws IOException
     * */
    private void copyDataBase() throws IOException {

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

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

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

        // transfer bytes from the inputfile to the outputfile
        final 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 final SQLiteDatabase openDataBase() {
        // Open the database
        final String myPath = DB_PATH + DB_NAME;
        if (myDataBase != null && myDataBase.isOpen()) {
            myDataBase.close();
        }
        return myDataBase = SQLiteDatabase.openDatabase(myPath, null,
                SQLiteDatabase.OPEN_READWRITE);

    }

    @Override
    public final synchronized void close() {
        if (myDataBase != null)
            myDataBase.close();
        super.close();
    }

    @Override
    public void onCreate(final SQLiteDatabase arg0) {
    }

    @Override
    public void onUpgrade(final SQLiteDatabase arg0, final int arg1,
            final int arg2) {
    }

}

Answer 2

CL 非常正确。我的复制代码是正确的，它没有被正确调用。我最终做的是草率，但我从查询代码而不是我的创建数据库中调用了 copyDataBase()。我知道愚蠢和低效，但它现在有效。

Answer 3

试试这个：

public class DBAdapter {

private static final String TAG = "[ DBAdapter ]";  
private static final String KEY_TOU_ID = "tournamentid";    
private static final String KEY_TEAM_ID = "teamid"; 
private static final String KEY_INNINGS_ID = "inningsid";
private static final int DATABASE_VERSION = 1;
private static final String DATABASE_NAME = "YourDbName";   
private static final String INNINGS_LIST_TABLE = "inningslist";



private static final String INNINGS_TABLE = "create table "
        + INNINGS_LIST_TABLE + "(" + KEY_INNINGS_ID
        + " integer primary key autoincrement," + KEY_GAME_ID + " integer,"
        + KEY_TEAM_ID + " integer," + KEY_TOU_ID + " integer);";

private DatabaseHelper DBhelper;
private SQLiteDatabase db;
private ProgressDialog pd;

public DBAdapter(Context ctx) {
    DBhelper = new DatabaseHelper(ctx);
}

private static class DatabaseHelper extends SQLiteOpenHelper {

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

    @Override
    public void onCreate(SQLiteDatabase db) {



        Log.i(TAG, "INNINGS TABLE" + INNINGS_LIST_TABLE);

        db.execSQL(INNINGS_TABLE);

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        Log.w(TAG, "Upgrading database from version " + oldVersion + " to "
                + newVersion + ", which will destroy all old data");
        db.execSQL("DROP TABLE IF EXISTS titles");
        onCreate(db);
    }
}

public DBAdapter open() {
    try {
        db = DBhelper.getWritableDatabase();
    } catch (SQLiteException sql) {
        sql.printStackTrace();
    }
    return this;
}

public boolean isCreated() {
    if (db != null) {
        return db.isOpen();
    }

    return false;
}

public boolean isOpen() {
    return db.isOpen();
}

public void close() {
    DBhelper.close();
    db.close();
}

}