商店產品的類表繼承：如何下訂單

Question

我想創建一個電子商務/商店系統，我決定在基於this great answer的SQL設計中選擇類表繼承設計。

現在我有如下表結構：

product (id [PK], name, description) 
product_shirt (id [PK], product_id [FK], color, size, stock, price) 
product_ring (id [PK], product_id [FK], size, stock, price) 
// maybe coming more 

這適用於網站上的產品的代表。但如果我想訂購一些產品，這將如何工作？

如果我有一張表用於我的產品，我可以將product_id作爲外鍵分配給關係表，但對於多個表，這似乎不再可行了。類表繼承有可能嗎？

我已經看了很多，大多數答案/教程似乎集中在產品的表示，但不是在客戶的秩序。

Answer 1

落場product_id從product_shirt和product_ring，使他們的id領域都主鍵和外鍵product.id。

您的order_item表將包含product.id的外鍵。

當您需要按給定順序提取有關產品的信息時，請僅通過連接進行查詢，並將其添加到product。當您需要特定產品的完整詳細信息時，還可以根據實際產品類型加入product_shirt或product_ring。

---

例子：

-- red XL shirt: product #1 
INSERT INTO product VALUE (1, 'Red XL shirt', 'What a lovely shirt'); 
INSERT INTO product_shirt VALUE (1, 'XL', 'red', 1, 12); 

-- blue S shirt: product #2 
INSERT INTO product VALUE (2, 'Blue S shirt', 'How nice a shirt'); 
INSERT INTO product_shirt VALUE (2, 'S', 'blue', 1, 12); 

-- small ring: product #3 
INSERT INTO product VALUE (3, 'Small ring', 'One to rule them all'); 
INSERT INTO product_ring VALUE (3, 'S', 1, 5); 

-- customer orders a "Blue S shirt" and a "Small ring": 
INSERT INTO order_item VALUES (
    1, -- order_number 
    2, -- product_id 
    1, -- quantity 
), (
    1, -- order_number 
    3, -- product_id 
    1, -- quantity 
); 

-- overview of the basket 
SELECT * FROM order_item 
JOIN product ON product.id = order_item.product_id 
WHERE order_number = 1; 

-- details of the basket contents 
-- -- this will only show details pertaining to products of type "shirt", if any 
SELECT * FROM order_item 
JOIN product ON product.id = order_item.product_id 
JOIN product_shirt ON product_shirt.id = product.id 
WHERE order_number = 1; 

-- -- this will only show details pertaining to products of type "ring", if any 
SELECT * FROM order_item 
JOIN product ON product.id = order_item.product_id 
JOIN product_ring ON product_ring.id = product.id 
WHERE order_number = 1; 

-- notice you cannot UNION these results as we expect a different number of columns 
-- your application classes are expected to handle these differences