如何更新我的库存数据库以在客户下订单后自行减少

Question

是时候再问一下万能的堆栈溢出问题了。所以我的问题是我正在 TKINTER 中开发，并在应用程序的一个数据库中实施和集成了 2 tables。我希望我的 table 产品在购物篮 table 上下订单后更新，并且在 self.data_entry 方法被调用后发生。问题是当我的 stock_update 方法运行时，它会更新数据库，但会擦除其他产品的库存价值。我只是想知道我的 stock_update 方法是否有错误的语法来更新 sql.

之前运行

product_id	product_name	stock
1	product1	60
1	product2	60

之后

product_id	product_name	stock
1	product1	59
1	product2	NULL

class 数据库处理程序：

def data_entry(self, cust_id, prod_id, prod_name, delivery_type, quantity, delivery_cost, price, subtotal):
    print("Data Entry Method is called")
    connection = sqlite3.connect("anothertrial.db")
    cursor = connection.cursor()
    # YA "value" in the following line should be "values"
    insert_query = "INSERT INTO basket(cust_id, product_id,  prod_name, delivery_type, quantity, delivery_cost, price, subtotal) VALUES(?,?,?,?,?,?,?,?)"
    cursor.execute(insert_query,
                   (cust_id, prod_id, prod_name, delivery_type, quantity, delivery_cost, price, subtotal))
    connection.commit()
    connection.close()
    print("Data Entry Method is finished")
def connection(self):
    print("Database is now connected")
    db_conn = sqlite3.connect("anothertrial.db")
    cursor = db_conn.cursor()
    my_query = "CREATE TABLE IF NOT EXISTS basket(order_id INTEGER PRIMARY KEY AUTOINCREMENT, cust_id TEXT, product_id INTEGER, prod_name TEXT, delivery_type TEXT, quantity TEXT, delivery_cost TEXT, price TEXT, subtotal TEXT, FOREIGN KEY (product_id) REFERENCES products(product_id)) "
    cursor.execute(my_query)
    db_conn.commit()
    db_conn.close()
    print("Database connection is finished")

def product_connection(self):
    print("Product Table Creation Method")
    db_connect = sqlite3.connect("anothertrial.db")
    cursor = db_connect.cursor()
    product_table_creation = "CREATE TABLE IF NOT EXISTS products(product_id INTEGER PRIMARY KEY AUTOINCREMENT, " \
                             "product_name TEXT, stock INTEGER)"
    cursor.execute(product_table_creation)
    db_connect.commit()
    db_connect.close()
    print("Product Table has been created")

def stock_update(self):
    print("Stock Update Method")  # I use Print to Test My Method If It Will Run
    db_connect = sqlite3.connect("anothertrial.db")
    cursor = db_connect.cursor()
    stock_update_query = "UPDATE products SET stock = stock - (SELECT quantity FROM basket WHERE " \
                         "basket.product_id = " \
                         "products.product_id) "
    cursor.execute(stock_update_query)
    db_connect.commit()
    db_connect.close()
    print("Stock Updated")  # I use Print to Test My Method If It Will Run


def add_item(self):
    global total
    global delivery_charge
    global chosen_item_id
    product_id_dict = {"Gundam": 1, "Starwars": 2, "Paw Patrol": 3, "Peppa Pig": 4, "Cars Disney": 5,
                       "Teddy Bear": 6}
    item_dict = {"": 0, "Gundam": 10, "Starwars": 20, "Paw Patrol": 30, "Peppa Pig": 15, "Cars Disney": 15,
                 "Teddy Bear": 10}

    delivery_dict = {"Free Delivery": 0, "Standard": 2, "Express": 5}

    delivery_type = self.delivery_opt_var.get()
    item = self.product_name_var.get()
    price = (self.prod_cost_var.get())
    qty = self.quantity_var.get()

    for product, cost in item_dict.items():
        for delivery, charge in delivery_dict.items():
            for selected_product, prod_id in product_id_dict.items():
                if item == product and delivery == delivery_type and item == selected_product:
                    chosen_item_id = prod_id
                    delivery_charge = charge
                    price = cost
                    total = round(price * qty + delivery_charge, 2)

    self.product_id_var.set(chosen_item_id)
    self.prod_cost_var.set(price)
    self.delivery_charge_var.set(delivery_charge)
    self.subtotal_var.set(total)

    self.customer_basket.data_entry(self.order_cust_id_var.get(),
                                    self.product_id_var.get(),
                                    self.product_name_var.get(),
                                    self.delivery_opt_var.get(),
                                    self.quantity_var.get(),
                                    self.delivery_charge_var.get(),
                                    self.prod_cost_var.get(),
                                    self.subtotal_var.get())

Answer 1

我修改了查询。希望这项工作：

stock_update_query = "UPDATE products SET stock = stock - (SELECT quantity FROM basket WHERE " \
                     "basket.product_id = " \
                     "products.product_id) " \
                     "WHERE EXISTS (SELECT quantity " \
                     "FROM basket "\
                     "WHERE product_id = products.product_id)"

如何更新我的库存数据库以在客户下订单后自行减少

How do I update my stock database to reduce itself once a customer orders

python

sql

sqlite

tkinter

tk