error when trying to update sqlite data base in adnroid

i had my data base working but all the records i have inserted were for checking purpose, now i wanted to delete all the tables and creating new ones, so i tryed updating the data base but changing the version. i didnt changed nothing on the create table querys but im getting the foreign key constraint failed (code 787). here is my DBHElper class:

private static final String DATABASE_NAME = "roomatesDB";

    //data base version
    private static final int DATABASE_VERSION = 3;

    //tables name
    public static final String APARTMENT_TABLE = "apartment";
    public static final String ROOMATE_TABLE = "roomate";
    public static final String SHOPCART_TABLE = "shopcart";
    public static final String ITEMS_TABLE = "items";

    //common column
    public static final String APARTMENT_NUMBER_COLUMN = "apartmentNum";

    //roomates table columns
    public static final String FIRST_NAME_COLUMN = "firstName";
    public static final String LAST_NAME_COLUMN = "lastName";
    public static final String PHONE_NUMBER_COLUMN = "phoneNumber";

    //shop cart table columns
    public static final String NUMBER_COLUMN = "number";
    public static final String LIST_NAME_COLUMN = "name";

    //item table
    public static final String PRICE_COLUMN = "price";
    public static final String ITEM_NAME_COLUMN = "name";

    //qeury for creating roomate table
    public static final String CREATE_ROOMATE_TABLE = "CREATE TABLE "
            + ROOMATE_TABLE + "(" + FIRST_NAME_COLUMN + " TEXT, "
            + LAST_NAME_COLUMN + " TEXT, " + PHONE_NUMBER_COLUMN + " TEXT, "
            + APARTMENT_NUMBER_COLUMN + " INTEGER, "
            + "FOREIGN KEY(" + APARTMENT_NUMBER_COLUMN + ") REFERENCES "
            + APARTMENT_TABLE + "(apartmentNum) " + ")";

    //query for crating shop cart table
    public static final String CREATE_SHOPLIST_TABLE = "CREATE TABLE "
            + SHOPCART_TABLE + "(" + NUMBER_COLUMN + " INTEGER PRIMARY KEY,"
            + LIST_NAME_COLUMN + " TEXT, "
            + APARTMENT_NUMBER_COLUMN + " INTEGER, "
            + "FOREIGN KEY(" + APARTMENT_NUMBER_COLUMN + ") REFERENCES "
            + APARTMENT_TABLE + "(apartmentNum) " + ")";

    //query for creating shop item table
    public static final String CREATE_SHOPITEM_TABLE = "CREATE TABLE "
            + ITEMS_TABLE + "(" + ITEM_NAME_COLUMN + " TEXT,"
            + PRICE_COLUMN + " DOUBLE, "
            + NUMBER_COLUMN + " INT, "
            + "FOREIGN KEY(" + NUMBER_COLUMN + ") REFERENCES "
            + SHOPCART_TABLE + "(number) " + ")";

    //query for creating apartment table
    public static final String CREATE_APARTMENT_TABLE = "CREATE TABLE "
            + APARTMENT_TABLE + "(" + APARTMENT_NUMBER_COLUMN + " INTEGER PRIMARY KEY"
            + ")";


    public DBHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);

    }

    public void onConfigure(SQLiteDatabase db) {
        super.onConfigure(db);
        db.setForeignKeyConstraintsEnabled(true);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(CREATE_APARTMENT_TABLE);
        db.execSQL(CREATE_ROOMATE_TABLE);
        db.execSQL(CREATE_SHOPLIST_TABLE);
        db.execSQL(CREATE_SHOPITEM_TABLE);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS " + APARTMENT_TABLE);
        db.execSQL("DROP TABLE IF EXISTS " + ROOMATE_TABLE);
        db.execSQL("DROP TABLE IF EXISTS " + SHOPCART_TABLE);
        db.execSQL("DROP TABLE IF EXISTS " + ITEMS_TABLE);

        onCreate(db);

    }