如何為postgres編寫DELETE CASCADE？

Question

我正在為postgres手動構建DELETE CASCADE語句。

我有一個'交易'和'切片'表，相關如下：

    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)

假設我想要刪除名稱為“my_slice”的切片引用的所有事務和classification_items。 我需要寫什么？

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

Answer 1

Postgres外鍵支持CASCADE刪除：

slice_id integer REFERENCES slice(id) ON DELETE CASCADE

等等

Answer 2

萬一你不能做別人的建議：

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

它是在表中定義的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

您應該使用CASCADE刪除，即使您繼承了數據庫模式，也應該可以這樣做。 您只需修改約束以將CASCADE刪除添加到模式：

1. 刪除並重新創建約束以添加CASCADE刪除：

    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. 現在，以下查詢不僅會從表slice刪除my_slice記錄，還會從表transaction和classification_item引用它的所有記錄：

    DELETE FROM slice WHERE name='my_slice'; 

即使原始模式由像SQLAlchemy這樣的對象關系映射器創建，該過程也會起作用。 但是，在這種情況下，每當架構更改或重新創建時，請務必重新應用該“補丁”。 只有當它不能自動實現時，它畢竟不是一個好主意......

Answer 5

可以通過設置約束屬性“On delete”= CASCADE將其委派給DBMS。 請看一個例子 。