一个在SQLite数据库Android的增量领域 [英] Increment the field by one in sqlite database android

问题描述

我有它重新presents店为我的比赛一个表的数据库。问题是，当我使用的方法来购买它并没有一个递增的价值，但只是将其设置为零。那么，如何可以通过提高各一个，它被称为特定ID时间递增ItemNumberOfPurchases的值的方法？这是我的code这一点。

 公共类MonsterTapDatabase扩展SQLiteOpenHelper {
静态最后弦乐DBNAME =MonsterTapDb;
静态最终诠释版本= 1;
静态最后弦乐tTableName =商店;
静态最后弦乐fItemID =项目ID;
静态最后弦乐fItemName =了itemname;
静态最后弦乐fItemNumberOfPurchases =NumberOfPurchases;
静态最后弦乐fItemIsLocked =IsItemLocked;


公共MonsterTapDatabase（上下文的背景下）{
    超（背景下，数据库名，空，版本）;
}

@覆盖
公共无效的onCreate（SQLiteDatabase sqLiteDatabase）{
    sqLiteDatabase.execSQL（CREATE TABLE IF NOT EXISTS+ tTableName +（+
            fItemID +INTEGER PRIMARY KEY，+
            fItemName +TEXT+
            fItemNumberOfPurchases +INT+
            fItemIsLocked +TEXT+
            ））;
    ContentValues​​ CV =新ContentValues​​（）;
    cv.put（fItemID，1）;
    cv.put（fItemName，住）;
    cv.put（fItemNumberOfPurchases，0）;
    cv.put（fItemIsLocked，真）;
    sqLiteDatabase.insert（tTableName，空，CV）;
    cv.put（fItemID，2）;
    cv.put（fItemNameHardmode）;
    cv.put（fItemNumberOfPurchases，0）;
    cv.put（fItemIsLocked，真）;
    sqLiteDatabase.insert（tTableName，空，CV）;
    cv.put（fItemID，3）;
    cv.put（fItemName，反向）;
    cv.put（fItemNumberOfPurchases，0）;
    cv.put（fItemIsLocked，真）;
    sqLiteDatabase.insert（tTableName，空，CV）;
    cv.put（fItemID，4）;
    cv.put（fItemName，反转Hardmode）;
    cv.put（fItemNumberOfPurchases，0）;
    cv.put（fItemIsLocked，真）;
    sqLiteDatabase.insert（tTableName，空，CV）;
}

@覆盖
公共无效onUpgrade（SQLiteDatabase sqLiteDatabase，诠释我，诠释I1）{
    sqLiteDatabase.execSQL（DROP TABLE IF EXISTS+ tTableName）;
    的onCreate（sqLiteDatabase）;
}
公共无效报价（INT ID）{

    SQLiteDatabase MYDB = this.getWritableDatabase（）;
    myDB.execSQL（UPDATE+ tTableName +
            SET+ fItemNumberOfPurchases += IFNULL（+ fItemNumberOfPurchases +，0）1+
            WHE​​RE+ fItemID +=+ ID）;
    myDB.close（）;

}
公共无效lockItem（INT ID）{
    SQLiteDatabase MYDB = this.getWritableDatabase（）;
    ContentValues​​ CV =新ContentValues​​（）;
    cv.put（fItemIsLocked，假）;
    myDB.update（tTableName，CV，fItemID +=？，新的String [] {将String.valueOf（ID）}）;
}
公共字符串isPurchased（INT ID）{
    SQLiteDatabase MYDB = this.getReadableDatabase（）;
    的String [] MYSEARCH =新的String [] {将String.valueOf（ID）};
    光标myCursor = myDB.rawQuery（选择+ fItemIsLocked +FROM+ tTableName +WHERE+ fItemID +=？，MYSEARCH）;
    myCursor.moveToFirst（）;
    INT指数= myCursor.getColumnIndex（fItemID）;
    字符串myAnswer = myCursor.getString（指数）;
    myCursor.close（）;
    返回myAnswer;
}
公众诠释numberOfLives（）{
    INT ID = 1;
    SQLiteDatabase MYDB = this.getReadableDatabase（）;
    的String [] MYSEARCH =新的String [] {将String.valueOf（ID）};
    光标myCursor = myDB.rawQuery（选择+ fItemNumberOfPurchases +FROM+ tTableName +WHERE+ fItemID +=？，MYSEARCH）;
    myCursor.moveToFirst（）;
    INT指数= myCursor.getColumnIndex（fItemNumberOfPurchases）;
    myCursor.close（）;
    返回指数;
}
 

}

解决方案

1. 您正在使用 fItemNumberOfPurchases 而不是 fItemID ;
2. 为什么你对子级比较有不平等ID？
3. 如果 fItemNumberOfPurchases 是 NULL ，运算与数字总是返回 NULL ，这可能与 IFNULL 处理。

修正：

  SQLiteDatabase MYDB = this.getWritableDatabase（）;
myDB.execSQL（UPDATE+ tTableName +
    SET+ fItemNumberOfPurchases += IFNULL（+ fItemNumberOfPurchases +，0）1+
    WHE​​RE+ fItemID +=+ ID）;
myDB.close（）;
 

I have a database with a table which represents Shop for my game. The problem is, that when I use the method to purchase it doesn't increment the value by one but just sets it to zero. So how can I improve the method to increment the value of ItemNumberOfPurchases by one each time it's called for specific ID ? Here is my code for this.

public class MonsterTapDatabase extends SQLiteOpenHelper {
static final String dbName = "MonsterTapDb";
static final int version = 1;
static final String tTableName = "Shop";
static final String fItemID = "ItemID";
static final String fItemName = "ItemName";
static final String fItemNumberOfPurchases = "NumberOfPurchases";
static final String fItemIsLocked = "IsItemLocked";


public MonsterTapDatabase(Context context) {
    super(context, dbName, null, version);
}

@Override
public void onCreate(SQLiteDatabase sqLiteDatabase) {
    sqLiteDatabase.execSQL("CREATE TABLE IF NOT EXISTS "+tTableName+" (" +
            fItemID + " INTEGER PRIMARY KEY , " +
            fItemName + " TEXT , " +
            fItemNumberOfPurchases + " INT, " +
            fItemIsLocked + " TEXT" +
            ")");
    ContentValues cv = new ContentValues();
    cv.put(fItemID, 1);
    cv.put(fItemName, "Lives");
    cv.put(fItemNumberOfPurchases, 0);
    cv.put(fItemIsLocked, "true");
    sqLiteDatabase.insert(tTableName, null, cv);
    cv.put(fItemID, 2);
    cv.put(fItemName, "Hardmode");
    cv.put(fItemNumberOfPurchases, 0);
    cv.put(fItemIsLocked, "true");
    sqLiteDatabase.insert(tTableName, null, cv);
    cv.put(fItemID, 3);
    cv.put(fItemName, "Reversed");
    cv.put(fItemNumberOfPurchases, 0);
    cv.put(fItemIsLocked, "true");
    sqLiteDatabase.insert(tTableName, null, cv);
    cv.put(fItemID, 4);
    cv.put(fItemName, "Reversed Hardmode");
    cv.put(fItemNumberOfPurchases, 0);
    cv.put(fItemIsLocked, "true");
    sqLiteDatabase.insert(tTableName, null, cv);
}

@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {
    sqLiteDatabase.execSQL("DROP TABLE IF EXISTS " + tTableName);
    onCreate(sqLiteDatabase);
}
public void purchase(int ID){

    SQLiteDatabase myDB = this.getWritableDatabase();
    myDB.execSQL("UPDATE " + tTableName+
            " SET "+fItemNumberOfPurchases+"=IFNULL("+fItemNumberOfPurchases+",0)+1"+
            " WHERE "+fItemID+"="+ID);
    myDB.close();

}
public void lockItem(int ID){
    SQLiteDatabase myDB = this.getWritableDatabase();
    ContentValues cv = new ContentValues();
    cv.put(fItemIsLocked, false);
    myDB.update(tTableName, cv, fItemID+"=?", new String []{String.valueOf(ID)});
}
public String isPurchased(int ID){
    SQLiteDatabase myDB = this.getReadableDatabase();
    String[] mySearch = new String[]{String.valueOf(ID)};
    Cursor myCursor = myDB.rawQuery("SELECT "+ fItemIsLocked +" FROM "+ tTableName +" WHERE "+ fItemID +"=?",mySearch);
    myCursor.moveToFirst();
    int index = myCursor.getColumnIndex(fItemID);
    String myAnswer = myCursor.getString(index);
    myCursor.close();
    return myAnswer;
}
public int numberOfLives(){
    int ID = 1;
    SQLiteDatabase myDB = this.getReadableDatabase();
    String[] mySearch = new String[]{String.valueOf(ID)};
    Cursor myCursor = myDB.rawQuery("SELECT "+ fItemNumberOfPurchases +" FROM "+ tTableName +" WHERE "+ fItemID +"=?",mySearch);
    myCursor.moveToFirst();
    int index = myCursor.getColumnIndex(fItemNumberOfPurchases);
    myCursor.close();
    return index;
}

}

解决方案

1. You are using fItemNumberOfPurchases instead of fItemID;
2. Why whould you compare a ID with a inequality?
3. If fItemNumberOfPurchases is NULL, arithmetic with numbers will always return NULL, which may be handled with IFNULL.

Corrected:

SQLiteDatabase myDB = this.getWritableDatabase();
myDB.execSQL("UPDATE " + tTableName+
    " SET "+fItemNumberOfPurchases+"=IFNULL("+fItemNumberOfPurchases+",0)+1"+
    " WHERE "+fItemID+"="+ID);
myDB.close();

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