我正在建立一个sqlite数据库，该数据库将存储有关产品的信息。是时候将新项添加到数据库了。当我确信应该存在该表列时，第一表列出现错误，提示不存在任何此类表列。我目前的问题是问题在于onCreate（）。我是sqlite的新手，正在为其他人着手工作，如果我忽略了一些基本知识，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;
}
}
这是我得到的错误
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)
答案 0 :(得分：1)
我认为您提供的代码没有任何问题。
这将复制您的代码，并在MainActivity中使用以下代码：-
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()
);
}
}
}
在日志中产生以下结果（如预期）：-
04-20 07:21:16.291 10005-10005/? D/ITEMFROMLIST: Item Name is tjastjtjjta
Initial Price = 0.0
Current Price = 1372.0450878788292
Price Change = 1372.0450878788292]n]tURL = tuarhwrqhh
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，但并未删除数据库（通过卸载应用程序来实现，删除应用程序的数据或增加数据库版本（删除表并重新创建表）。
删除数据库的原因是 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。
如果用于开发的设备具有可使用的/已启用的备份管理器，并且应用程序的清单中包含android:allowBackup="true"，则可能会还原该应用程序的数据，从而有效地避免了卸载应用程序或清除应用程序的操作数据。将清单更改为使用android:allowBackup="false"可以解决此类问题。
在这种情况下，增加数据库版本也将起作用，因为它不依赖于要删除的数据库。而是在调用 onUpgrade 方法时起作用，此DROP是表，并调用 onCreate 方法。
我还建议对 getAllItems 方法（注释解释）进行一些更改，例如：-
/** 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;
}