SQLAlchemy:如何使用join删除

Question

我无法用SQLAlchemy做这样的事情:

DELETE a FROM a INNER JOIN b ON b.`aId` = a.`Id` WHERE `b`.`xxx` = ?;

正如这里的帖子:SQLAlchemy:在MySQL上使用自联接创建删除查询

我已经很难在SQLAlchemy中使用join进行删除.

所以我现在这样做:

session.execute('DELETE a FROM a INNER JOIN b ON b.`aId` = a.`Id` WHERE `b`.`xxx` = %d;'%xxx)

但它只是让我很烦恼:SQL注入事物等等.

有没有办法使用SQLAlchemy来解决这个问题？谢谢!

Answer 1

这是我的做法：

map_ids = session.query(Table1.map_id). \
    filter(Table1.xxxx == 'xxx_value')

q = session.query(Table2). \
    filter(Table2.map_id.in_(map_ids.subquery()))

q.delete(synchronize_session=False)

这里的关键是您通过查找必须删除的 id 来创建子查询。然后使用“in_”运算符选择要删除的记录。'synchoronize_session=False' 将在不更新会话的情况下执行查询。这提供了最佳的性能提升。

Answer 2

SQLAlchemy 1.2 及更高版本支持某些方言的多表删除（在编写 Postgresql、MySQL 和 Microsoft SQL Server 时）：

In [18]: a = table('a', column('x'))

In [19]: b = table('b', column('x'))

In [20]: c = table('c', column('x'), column('y'))

In [21]: a.delete().\
    ...:     where(a.c.x == b.c.x).\
    ...:     where(b.c.x == c.c.x).\
    ...:     where(c.c.y == 1)
Out[21]: <sqlalchemy.sql.dml.Delete object at 0x7f3577d89160>

In [22]: print(_.compile(dialect=mysql.dialect()))
DELETE FROM a USING a, b, c WHERE a.x = b.x AND b.x = c.x AND c.y = %s

同样使用 aSession和 Declarative：

In [2]: class Foo(Base):
   ...:     __tablename__ = 'foo'
   ...:     id = Column(Integer, primary_key=True)

In [3]: class Bar(Base):
   ...:     __tablename__ = 'bar'
   ...:     id = Column(Integer, primary_key=True)
   ...:     foo_id = Column(ForeignKey(Foo.id))
   ...:     

In [4]: class Baz(Base):
   ...:     __tablename__ = 'baz'
   ...:     id = Column(Integer, primary_key=True)
   ...:     bar_id = Column(ForeignKey(Bar.id))
   ...:     val = Column(Integer)
   ...:     

In [5]: session.query(Foo).\
   ...:     filter(Foo.id == Bar.foo_id,
   ...:            Bar.id == Baz.bar_id,
   ...:            Baz.val == 1).\
   ...:     delete(synchronize_session=False)
   ...:            

哪个会发出

DELETE FROM foo USING foo, bar, baz
WHERE foo.id = bar.foo_id AND bar.id = baz.bar_id AND baz.val = %(val_1)s