Question

我有一个名为'products3'的表，其中包含列'id'，'type'，'width'，'length'，'thickness'，'quantity'..（按顺序）而不是'type'所有其他列都是'int' 我希望选择数量并通过过滤其他列上的数据来返回它。方法'findproduct'中的游标在if条件中返回false或NULL，即使数据存在于表中我使用DB浏览器浏览SQLite !!请帮忙

    public class MyDBHandler extends SQLiteOpenHelper {

    int s;
    private static final int DATABASE_VERSION = 1;
    private static final String DATABASE_NAME = "productDB3.db";
    private static final String TABLE_PRODUCTS = "products3";

    public static final String COLUMN_ID = "_id";
    public static final String COLUMN_TYPE = "type";
    public static final String COLUMN_QUANTITY = "quantity";
    public static final String COLUMN_WIDTH = "width";
    public static final String COLUMN_LENGTH = "length";
    public static final String COLUMN_THICK = "thick";

    public MyDBHandler(Context context, String name,
                       SQLiteDatabase.CursorFactory factory, int version) {
        super(context, DATABASE_NAME, factory, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String CREATE_PRODUCTS_TABLE = "CREATE TABLE " +
                TABLE_PRODUCTS + "("
                + COLUMN_ID + " INTEGER PRIMARY KEY autoincrement," + COLUMN_TYPE
                + " TEXT," + COLUMN_WIDTH + " INTEGER," + COLUMN_LENGTH + " INTEGER," + COLUMN_THICK + " INTEGER,"
                + COLUMN_QUANTITY + " INTEGER" + ")";
        db.execSQL(CREATE_PRODUCTS_TABLE);

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion,
                          int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_PRODUCTS);
        onCreate(db);

    }

    public void addProduct(String type,int width,int length,int thick,int quant) {


        ContentValues values = new ContentValues();
        values.put(COLUMN_TYPE,type);
        values.put(COLUMN_WIDTH,width);
        values.put(COLUMN_LENGTH,length);
        values.put(COLUMN_THICK,thick);
        values.put(COLUMN_QUANTITY,quant);

        SQLiteDatabase db = this.getWritableDatabase();

        db.insert(TABLE_PRODUCTS, null, values);
        db.close();
    }

    public int findProduct(String type,int width,int length,int thick) {

        String query = "SELECT quantity FROM products3 WHERE type='" + type +"' AND width=" + width + " AND length=" +
                length+" AND thick=" + thick + ";";
        SQLiteDatabase db = this.getWritableDatabase();

        if (cursor.moveToFirst()) {

            cursor.moveToFirst();

           s=cursor.getInt(0);

            cursor.close();
            return s;
        }
        db.close();
        return 0;
       }

    public boolean deleteProduct(String type,int width,int length,int thick) {



        SQLiteDatabase db = this.getWritableDatabase();
        db.execSQL("DELETE FROM products3 WHERE type='" + type +"' and width=" + width + " and length=" +
                length+" and thick=" + thick );
        db.close();
           }
}

Answer 1

如果您在调试SQL查询时遇到问题，Android会提供一个方便的方法DatabaseUtils.dumpCursorToString()，将整个Cursor格式化为String。然后，您可以将转储输出到LogCat并查看查询结果。

cursor.moveToFirst（）返回false，即使表中存在数据

1 个答案: