Question

我在SQLite中创建了一个表，我想在用户可以将该值添加到表之前检查该值是否存在。请检查下面的代码：

//check if value exists

Cursor checkIfExist = shoppingListDB.rawQuery("SELECT *    FROM "+ selected_spinner + " WHERE " + "ITEM_NAME  = " + "'" + add_tems + "'", null);

if (checkIfExist == null) {
    String insert_data="INSERT INTO " +   selected_spinner + " (ITEM_NAME,SHOP_LIST,NUMB_ITEMS) VALUES " + "('" + add_tems + "'," + "'" + add_shop + "'," + "'" + add_quantity + "'" + ")";
    shoppingListDB.execSQL(insert_data);
} else 
    Toast.makeText(getBaseContext(), " " + add_tems + " Exists", Toast.LENGTH_LONG).show();

Answer 1

试试这种方式，

Cursor checkIfExist = shoppingListDB.rawQuery("SELECT *    FROM "+ selected_spinner + " WHERE " + "ITEM_NAME  = " + "'" + add_tems + "'", null);

checkIfExist.moveToFirst(); 

        if ( checkIfExist.getCount() > 0 ) 
        {
            String insert_data="INSERT INTO " +   selected_spinner + " (ITEM_NAME,SHOP_LIST,NUMB_ITEMS) VALUES " + "('" + add_tems + "'," + "'" + add_shop + "'," + "'" + add_quantity + "'" + ")";
            shoppingListDB.execSQL(insert_data);

        } 
        else 
        {
            Toast.makeText(getBaseContext(), " " + add_tems + " Exists", Toast.LENGTH_LONG).show();
        }

Answer 2

执行else子句是因为Cursor对象永远不会为null。 rawQuery（）总是返回一个Cursor对象。因此，您需要测试sql查询是否影响了一行或多行：

if(checkIfExist.moveToFirst()){
    //value exist
}else{
    //value does not exist
}

如果Cursor为空（doc）

，

moveToFirst（）将返回false

Answer 3

这是一个实施问题。您可以更改方法，以使用List

中的所有对象返回Database

类似的东西：

public List<Item> getAllItems() {
    List<Item> items = new LinkedList<Item>();

    // 1. build the query
    String query = "SELECT  * FROM " + selected_spinner;

    // 2. get reference to writable DB
    SQLiteDatabase db = this.getWritableDatabase();
    Cursor cursor = db.rawQuery(query, null);

    // 3. go over each row, build item and add it to list
    Item item = null;
    if (cursor.moveToFirst()) {
        do {
            item = new Item ((cursor.getString(1)), cursor.getString(2));
            item .setId(Integer.parseInt(cursor.getString(0)));
            // Add item to items
            items.add(item);
        } while (cursor.moveToNext());
    }

    Log.d("getAllItems()", items.toString());

    // return items
    return items;
}

然后，您可以调用该方法：

boolean valueExist = false;

private List<String> nameOfItems = new ArrayList<String>();

private static List<Item> itemList = null;

DataBaseHelper db = new DataBaseHelper(this);

itemList = db.getAllItems();

db.close();

if(itemList .size() != 0){
    for(Item i : itemList ){
        nameOfItems .add(i.getName());
    }
}

最后检查值是否存在......

if(nameOfItems.contains(//Any String that you might want to check){
    valueExist = true;
}

检查SQLite中是否存在值。如果存在，则提醒用户该值存在

3 个答案: