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django orm 更新 model 某个字段为该 model 中某个外键 mode 字段的值。

5 replies • 2019-02-17 22:15:00 +08:00

kingofvir

Jan 24, 2019

有 model A，model B，A.b = ForeignKey(B)，如优雅地设置 A.author = A.b.name.

kingofvir

Jan 25, 2019

自顶

mayorbryant

Jan 25, 2019

难道 A.author = A.b.name 就不优雅了吗

kingofvir

Jan 28, 2019

@mayorbryant 主要是为了数据更新，这样几万条数据更新需要执行几万个 sql

banxi1988

Feb 17, 2019

根据我的理解给出一个使用纯 SQL 的解法，你可以自行翻译成 Django ORM 的写法
针对如下表结构：

```sql
CREATE TABLE `author` (
`id` INTEGER,
`name` TEXT,
PRIMARY KEY(`id`)
);

CREATE TABLE `book` (
`id` INTEGER,
`name` TEXT NOT NULL,
`author_id` INTEGER,
`author_name` TEXT,
PRIMARY KEY(`id`)
);

````

`book.author_name` 是后面加的，要填充其关联的 author 的名称可以使用如下 SQL 语句更新。

```sql
update book set author_name = (select name from author where id = author_id)
```
经过我使用 SQLite 测试是 OK 的。
> Query executed successfully: update book set author_name = (select name from author where id = author_id) (took 0ms, 3 rows affected)