如何为postgres编写DELETE CASCADE？

Question

我正在为postgres手动构建DELETE CASCADE语句。

我有一个'交易'和'切片'表，相关如下：

    Table "public.slice"
  Column  | Type | Modifiers 
----------+------+-----------
 id       | text | not null
 name     | text | 
Referenced by:
    TABLE "transaction" CONSTRAINT "transaction_slice_id_fkey" FOREIGN KEY (slice_id) REFERENCES slice(id)
 Table "public.transaction"
  Column  | Type | Modifiers 
----------+------+-----------
 id       | text | not null
 slice_id | text | 
Referenced by:
    TABLE "classification_item" CONSTRAINT "classification_item_transaction_id_fkey" FOREIGN KEY (transaction_id) REFERENCES transaction(id)
Table "public.classification_item"
     Column     | Type | Modifiers 
----------------+------+-----------
 id             | text | not null
 transaction_id | text | 
Foreign-key constraints:
    "classification_item_transaction_id_fkey" FOREIGN KEY (transaction_id) REFERENCES transaction(id)

假设我想要删除名称为“my_slice”的切片引用的所有事务和classification_items。 我需要写什么？

=# delete from classification_item where transaction_id= #...? 
=# delete from transaction where slice_id= #...? 
=# delete from slice where name='my_slice';

Answer 1

Postgres外键支持CASCADE删除：

slice_id integer REFERENCES slice(id) ON DELETE CASCADE

等等

Answer 2

万一你不能做别人的建议：

begin;
delete from classification_item where transaction_id in (select id from "transaction" where slice_id = (select id from slice where name = 'my_slice'));
delete from "transaction" where slice_id in (select id from slice where name='my_slice');
delete from slice where name='my_slice';
commit;

Answer 3

它是在表中定义的soemthing而不是DELETE Query。 示例（查看order_id）：

CREATE TABLE order_items (
    product_no integer REFERENCES products ON DELETE RESTRICT,
    order_id integer REFERENCES orders ON DELETE CASCADE,
    quantity integer,
    PRIMARY KEY (product_no, order_id)
);

Answer 4

您应该使用CASCADE删除，即使您继承了数据库模式，也应该可以这样做。 您只需修改约束以将CASCADE删除添加到模式：

1. 删除并重新创建约束以添加CASCADE删除：

    ALTER TABLE ONLY "transaction" DROP CONSTRAINT transaction_slice_id_fkey; ALTER TABLE ONLY "transaction" ADD CONSTRAINT transaction_slice_id_fkey FOREIGN KEY (slice_id) REFERENCES slice(id) ON DELETE CASCADE; ALTER TABLE ONLY "classification_item" DROP CONSTRAINT classification_item_transaction_id_fkey; ALTER TABLE ONLY "classification_item" ADD CONSTRAINT classification_item_transaction_id_fkey FOREIGN KEY (transaction_id) REFERENCES transaction(id) ON DELETE CASCADE; 

2. 现在，以下查询不仅会从表slice删除my_slice记录，还会从表transaction和classification_item引用它的所有记录：

    DELETE FROM slice WHERE name='my_slice'; 

即使原始模式由像SQLAlchemy这样的对象关系映射器创建，该过程也会起作用。 但是，在这种情况下，每当架构更改或重新创建时，请务必重新应用该“补丁”。 只有当它不能自动实现时，它毕竟不是一个好主意......

Answer 5

可以通过设置约束属性“On delete”= CASCADE将其委派给DBMS。 请看一个例子 。