使用 Python 时“ON DELETE CASCADE”不起作用

Question

在这里，我提供了一个完全可重现的代码，它演示了整个问题。问题是，当我从“父”表中删除行时，不会删除“子”表中的相应行，即使它们具有ON DELETE CASCADE指定的外键。所以这是代码：

>>> import sqlite3
>>> cnx = sqlite3.connect("mytest.db")
>>> cursor = cnx.cursor()
>>> cnx.execute("BEGIN")
<sqlite3.Cursor object at 0x7f0ab0923490>
>>> cursor.execute("CREATE TABLE test_table (id integer)")
<sqlite3.Cursor object at 0x7f0ab0923420>
>>> cursor.execute("CREATE UNIQUE INDEX id_primary ON test_table(id)")
<sqlite3.Cursor object at 0x7f0ab0923420>
>>> cursor.execute("INSERT INTO test_table (id) VALUES (1),(2),(3)")
<sqlite3.Cursor object at 0x7f0ab0923420>
>>> cursor.execute("CREATE TABLE test_table_2(id_fk integer, txt text,  FOREIGN KEY (id_fk) REFERENCES test_table(id) ON DELETE CASCADE)")
<sqlite3.Cursor object at 0x7f0ab0923420>
>>> cursor.execute("INSERT INTO test_table_2 (id_fk, txt) VALUES (1,\"one\"),(2,\"two\"),(3,\"three\")")
<sqlite3.Cursor object at 0x7f0ab0923420>
>>> res = cursor.execute("SELECT * FROM test_table_2")
>>> res
<sqlite3.Cursor object at 0x7f0ab0923420>
>>> for r in res:
...     print(r)
...
(1, 'one')
(2, 'two')
(3, 'three')
>>> cursor.execute("PRAGMA foreign_keys = ON")
<sqlite3.Cursor object at 0x7f0ab0923420>
>>> cursor.execute("DELETE FROM test_table WHERE id = 1")
<sqlite3.Cursor object at 0x7f0ab0923420>
>>> res = cursor.execute("SELECT * FROM test_table_2")
>>> for r in res:
...     print(r)
...
(1, 'one')
(2, 'two')
(3, 'three')

如您所见，我什至在执行PRAGMA foreign_keys = ON之前明确地运行DELETE，但这无济于事。顺便说一句，如果我在sqlite3>提示符下运行这些命令，则一切正常。所以，整个问题出在Python图书馆。

Answer 1

该FOREIGN_KEYS编译是一个交易的无操作里面。

此 pragma 是事务中的 no-op；只有在没有挂起的 BEGIN 或 SAVEPOINT 时，才能启用或禁用外键约束强制执行。