Java 未创建或识别Android SQLite表列。我错过了什么？

我正在建立一个sqlite数据库，它将存储有关产品的信息。将新项目添加到数据库时。当我确信第一个表列应该存在时，第一个表列出现错误，表示不存在这样的表列。我目前的想法是，问题在于onCreate。我是sqlite的新手，正在为其他人做这件事，如果我忽略了一些基本的东西，请原谅

public class itemDB extends SQLiteOpenHelper {
    /**Information*/
    private static final int DATABASE_VERSION = 1;
    private static final String DATABASE_NAME = "ProductInfoDB";
    private static final String TABLE_NAME = "ProductInfo_Table";
    public static final String COL_PRODUCTNAME = "ProductName";
    public static final String COL_INITIALPRICE = "InitialPrice";
    public static final String COL_CURRENTPRICE = "CurrentPrice";
    public static final String COL_PRICECHANGE = "PriceChange";
    public static final String COL_ITEMWEBPAGE = "ItemWebPage";

    /** Constructor */
    public itemDB(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    /**Creates the table
     * @param db Takes the database and creates a table on it
     * */
    @Override
    public void onCreate(SQLiteDatabase db) {
        String table =("CREATE TABLE IF NOT EXISTS " + TABLE_NAME + "( "
                + COL_PRODUCTNAME  +  " TEXT PRIMARY KEY,"
                + COL_INITIALPRICE +  " REAL,"
                + COL_CURRENTPRICE +  " REAL,"
                + COL_PRICECHANGE  +  " REAL,"
                + COL_ITEMWEBPAGE  +  " TEXT " + ") ");
        db.execSQL(table);
    }
    /**needed for database
     * Checks if table exists or not
     * */
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
        onCreate(db);
    }
    /** This method adds items to the table of the database
     * @param item, takes an item and gets its info, then places it on the table of the database
     * */
    public void addItem(Item item) {
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues contentValues = new ContentValues();
        contentValues.put(COL_PRODUCTNAME,item.getName());
        contentValues.put(COL_INITIALPRICE,item.getPriceInitial());
        contentValues.put(COL_CURRENTPRICE,item.getPriceCurrent());
        contentValues.put(COL_PRICECHANGE,item.getPriceChange());
        contentValues.put(COL_ITEMWEBPAGE,item.getUrl());
        db.insert(TABLE_NAME,null ,contentValues);
        db.close();
    }
    /** Methods aids in updating items on database
     * */
    public void updateItem(String oldName, Item item){
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues values = new ContentValues();

        values.put(COL_PRODUCTNAME,item.getName());
        values.put(COL_INITIALPRICE,item.getPriceInitial());
        values.put(COL_CURRENTPRICE,item.getPriceCurrent());
        values.put(COL_PRICECHANGE,item.getPriceChange());
        values.put(COL_ITEMWEBPAGE,item.getUrl());

        db.update(TABLE_NAME, values, COL_PRODUCTNAME + " = ?", new String[]{oldName});
        db.close();

    }
    /** This method returns all the items found on the table of the database,
     * recurses the table and returns a list of items
     * */
    public List<Item> getAllItems() {
        List<Item> items = new ArrayList<>();
        String selectQuery = "SELECT * FROM " + TABLE_NAME;
        SQLiteDatabase db = this.getReadableDatabase();
        Cursor cursor = db.rawQuery(selectQuery, null);
        if(cursor.getCount() > 0) {
            if (cursor.moveToFirst()) {
                do {
                    String itemName = cursor.getString(0);
                    double initialP = cursor.getDouble( 1);
                    double currentP = cursor.getDouble(2);
                    double priceC = cursor.getDouble(3);
                    String itemUrl = cursor.getString(4);

                    Item holder = new Item(itemName, initialP, currentP, priceC, itemUrl);
                    items.add(holder);
                } while (cursor.moveToNext());
            }
        }
        return items;
    }
}

以下是我得到的错误

2019-04-19 14:14:55.490 11936-11936/edu.package E/SQLiteLog: (1) table ProductInfo_Table has no column named ProductName
2019-04-19 14:14:55.500 11936-11936/edu.packageE/SQLiteDatabase: Error inserting ProductName=tjastjtjjta PriceChange=0.0 CurrentPrice=1372.0450878788292 InitialPrice=1372.0450878788292 ItemWebPage=tuarhwrqhh
    android.database.sqlite.SQLiteException: table ProductInfo_Table has no column named ProductName (code 1): , while compiling: INSERT INTO ProductInfo_Table(ProductName,PriceChange,CurrentPrice,InitialPrice,ItemWebPage) VALUES (?,?,?,?,?)
        at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method)
        at android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:895)
        at android.database.sqlite.SQLiteConnection.prepare(SQLiteConnection.java:506)
        at android.database.sqlite.SQLiteSession.prepare(SQLiteSession.java:726)
        at android.database.sqlite.SQLiteProgram.<init>(SQLiteProgram.java:58)
        at android.database.sqlite.SQLiteStatement.<init>(SQLiteStatement.java:31)
        at android.database.sqlite.SQLiteDatabase.insertWithOnConflict(SQLiteDatabase.java:1580)
        at android.database.sqlite.SQLiteDatabase.insert(SQLiteDatabase.java:1453)
        at edu.utep.cs.cs4330.homework3.itemDB.addItem(itemDB.java:68)
        at edu.utep.cs.cs4330.homework3.MainActivity.addItem(MainActivity.java:262)
        at edu.utep.cs.cs4330.homework3.EntryDialog$1.onClick(EntryDialog.java:66)
        at com.android.internal.app.AlertController$ButtonHandler.handleMessage(AlertController.java:164)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:154)
        at android.app.ActivityThread.main(ActivityThread.java:6313)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:872)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:762)

---

我认为您提供的代码没有任何问题

即复制代码并在Main活动中使用以下内容：-

public class MainActivity extends AppCompatActivity {

    itemDB ItemDBHlpr;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        ItemDBHlpr = new itemDB(this);
        Item myItem = new Item("tjastjtjjta",0.0,1372.0450878788292,1372.0450878788292,"tuarhwrqhh");
        ItemDBHlpr.addItem(myItem);
        List<Item> myItemList = ItemDBHlpr.getAllItems();
        for (Item i: myItemList) {
            Log.d("ITEMFROMLIST",
                    "Item Name is " + i.getName() +
                            "\n\tInitial Price = " + String.valueOf(i.getPriceInitial()) +
                            "\n\tCurrent Price = " + String.valueOf(i.getPriceCurrent()) +
                            "\n\tPrice Change = " + String.valueOf(i.getPriceChange()) +
                            "]n]tURL = " + i.getUrl()
            );
        }
    }
}

可能的问题 因此，问题很可能是应用程序已运行，然后进行了更改，将ProductName添加到表的定义中，但数据库未被删除。通过卸载应用程序、删除应用程序的数据或（在您的情况下）增加数据库版本，会删除表并重新创建表

删除数据库之所以有效，是因为onCreate方法仅在创建数据库时自动运行

增加数据库版本号会导致调用onUpgrade方法。这将删除并重新创建表

另一个原因 如果用于开发的设备有一个工作/启用的备份管理器，并且应用程序的清单有android:allowBackup=true，则有可能恢复应用程序的数据，从而有效地取消卸载应用程序或清除应用程序的数据。将清单更改为使用android:allowBackup=false可以克服这些问题

在这种情况下，增加数据库版本也会起作用，因为它不依赖于要删除的数据库。相反，它在调用onUpgrade方法时起作用，这个DROP是表，而调用onCreate方法

注：这取决于在本问题中相应编码的onUpgrade。 附加的 我还建议对getAllItems方法进行一些修改，注释解释如下：-

/** This method returns all the items found on the table of the database,
 * recurses the table and returns a list of items
 * */
public List<Item> getAllItems() {
    List<Item> items = new ArrayList<>();
    //String selectQuery = "SELECT * FROM " + TABLE_NAME; //<<<<<<<<<< COMMENTED OUT not needed as query method builds the SQL
    SQLiteDatabase db = this.getReadableDatabase();
    //Cursor cursor = db.rawQuery(selectQuery, null);
    // Generally recommended to use the query Convenience method rate than rawQuery
    Cursor cursor = db.query(TABLE_NAME,null,null,null,null,null,null);

    // No Need to do multiple checks for the same i.e. moveTo will return false if the move cannot be made
    //  if no rows then moveToNext returns false so loop ended
    //  if at last row then moveToNext will return false thus loop ended
    while (cursor.moveToNext()) {
                // Rather than hard coding offsets (which could change over time)
                // better to get the offset according to the column name
                String itemName = cursor.getString(cursor.getColumnIndex(COL_PRODUCTNAME));
                double initialP = cursor.getDouble( cursor.getColumnIndex(COL_INITIALPRICE));
                double currentP = cursor.getDouble(cursor.getColumnIndex(COL_CURRENTPRICE));
                double priceC = cursor.getDouble(cursor.getColumnIndex(COL_PRICECHANGE));
                String itemUrl = cursor.getString(cursor.getColumnIndex(COL_ITEMWEBPAGE));
                //Item holder = new Item(itemName, initialP, currentP, priceC, itemUrl); // No need for intermediate Item
                items.add(new Item(itemName, initialP, currentP, priceC, itemUrl)); //<<<<<<<<<< CHANGED
    }
    return items;
}

---

您可能更改了列的名称。从设备上卸载应用程序，然后重新运行以重新创建表。@对于PAS，仍然会出现相同的错误。是否可以尝试增加数据库版本以查看是否有帮助？请检查清单。你有这个属性吗：android:allowBackup=true？@forpas是的，它已经存在了。很好的解释，迈克！我在想这样的事情。我认为AndroidManifest.xml中的allowBackup=true实际上是造成问题的原因。旧的数据库文件没有被删除。@ReazMurshed我从来没有遇到过这个问题，总是使用默认值true，但我通常只使用模拟器。现在看看这方面。

/** This method returns all the items found on the table of the database,
 * recurses the table and returns a list of items
 * */
public List<Item> getAllItems() {
    List<Item> items = new ArrayList<>();
    //String selectQuery = "SELECT * FROM " + TABLE_NAME; //<<<<<<<<<< COMMENTED OUT not needed as query method builds the SQL
    SQLiteDatabase db = this.getReadableDatabase();
    //Cursor cursor = db.rawQuery(selectQuery, null);
    // Generally recommended to use the query Convenience method rate than rawQuery
    Cursor cursor = db.query(TABLE_NAME,null,null,null,null,null,null);

    // No Need to do multiple checks for the same i.e. moveTo will return false if the move cannot be made
    //  if no rows then moveToNext returns false so loop ended
    //  if at last row then moveToNext will return false thus loop ended
    while (cursor.moveToNext()) {
                // Rather than hard coding offsets (which could change over time)
                // better to get the offset according to the column name
                String itemName = cursor.getString(cursor.getColumnIndex(COL_PRODUCTNAME));
                double initialP = cursor.getDouble( cursor.getColumnIndex(COL_INITIALPRICE));
                double currentP = cursor.getDouble(cursor.getColumnIndex(COL_CURRENTPRICE));
                double priceC = cursor.getDouble(cursor.getColumnIndex(COL_PRICECHANGE));
                String itemUrl = cursor.getString(cursor.getColumnIndex(COL_ITEMWEBPAGE));
                //Item holder = new Item(itemName, initialP, currentP, priceC, itemUrl); // No need for intermediate Item
                items.add(new Item(itemName, initialP, currentP, priceC, itemUrl)); //<<<<<<<<<< CHANGED
    }
    return items;
}