如何使用 sequelize model.findAll() 获取表的最大值

Question

我有一个用例，必须将对 Products 表所做的每个更改存储为已更改行的版本。所以我的表由如下行组成：

https://i.stack.imgur.com/zXJ8S.png

所以，当我们使用model.findAll() 时，它将返回所有行，包括每行的版本。这对于历史视图来说很好。这里的问题是，我们如何在不返回以前版本（旧更改）的情况下获取表中所有最新版本的行？我有点担心我们可以使用 sequelize max 属性来实现这一点。但不确定如何使用它来实现我的用例。谁能告诉我该怎么做？谢谢

Answer 1

拍续集之前

有几种方法可以解决，尽管子查询是您可以做到的方法之一。

我已经演示了在 where 子句中添加一个带有 max 函数的子查询。

让我们首先在简单的mysql中复制它

mysql> create table product (productId VARCHAR(200), docversion integer, name VARCHAR(200), price integer, location VARCHAR(200));
Query OK, 0 rows affected (1.01 sec)

mysql> insert into product(productID, docversion, name, price, location) VALUES('PID123', 0, 'Chair', 25, 'USA');
Query OK, 1 row affected (0.07 sec)

mysql> insert into product(productID, docversion, name, price, location) VALUES('PID123', 1, 'Chair', 32, 'USA');
Query OK, 1 row affected (0.12 sec)

mysql> insert into product(productID, docversion, name, price, location) VALUES('PID456', 0, 'Table', 39, 'UK');
Query OK, 1 row affected (0.16 sec)

mysql> insert into product(productID, docversion, name, price, location) VALUES('PID456', 1, 'Table', 43, 'Canada');
Query OK, 1 row affected (0.08 sec)

mysql> insert into product(productID, docversion, name, price, location) VALUES('PID123', 2, 'Chair', 29, 'UK');
Query OK, 1 row affected (0.09 sec)

mysql> select * from product;
+-----------+------------+-------+-------+----------+
| productId | docversion | name  | price | location |
+-----------+------------+-------+-------+----------+
| PID123    |          0 | Chair |    25 | USA      |
| PID123    |          1 | Chair |    32 | USA      |
| PID456    |          0 | Table |    39 | UK       |
| PID456    |          1 | Table |    43 | Canada   |
| PID123    |          2 | Chair |    29 | UK       |
+-----------+------------+-------+-------+----------+
5 rows in set (0.00 sec)


mysql> select * from product where  location='USA' AND name='Chair' AND docversion = (select max(docversion) from product where location='USA' AND name='Chair' group by productId);
+-----------+------------+-------+-------+----------+
| productId | docversion | name  | price | location |
+-----------+------------+-------+-------+----------+
| PID123    |          1 | Chair |    32 | USA      |
+-----------+------------+-------+-------+----------+
1 row in set (0.01 sec)

现在将相同的查询转换为 sequelize

product.findAll({
  where: {
      location:{
          [Op.eq]: 'USA',
      },
      name:{
          [Op.eq]: 'Chair',
      },
      docversion:{
          [Op.eq]: sequelize.literal(`select max(docversion) from product where location='USA' AND name='Chair' group by productId`),
      },
  }
})