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,以下查询不仅会删除my_slice表中的记录,还会删除表中的slice所有记录transaction并classification_item引用它:

   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......