我需要执行下一个查询：
DELETE FROM <table_name>
ORDER BY <column_name> DESC LIMIT 1
我尝试：
query = session.query(MyTable)
query.order_by(MyTable.my_column.desc()).limit(1).delete()
error: Can't call Query.update() or Query.delete() when order_by() has been called
我目前的方式（我想摆脱循环）：
query = session.query(MyTable)
for item in query.order_by(MyTable.my_column.desc()).limit(1).all():
query.filter(MyTable.id == item.id).delete()
由于您正在处理 ORM 对象，因此您只需检索“最后一个”项目然后将其删除：
# ORM class for demo
class Team(Base):
__tablename__ = "team"
id = Column(Integer, primary_key=True)
name = Column(String(50))
rank = Column(Integer)
def __repr__(self):
return f"<Team(id={self.id}, name='{self.name}', rank={self.rank})>"
Base.metadata.drop_all(engine)
Base.metadata.create_all(engine)
# test data
with Session(engine) as session:
session.add_all(
[
Team(name="Oilers", rank=3),
Team(name="Flames", rank=1),
Team(name="Canucks", rank=2),
]
)
session.commit()
# demo code
with Session(engine) as session:
last_place_team = session.execute(
select(Team).order_by(Team.rank.desc()).limit(1)
).scalar()
print(last_place_team) # <Team(id=1, name='Oilers', rank=3)>
session.delete(last_place_team)
session.commit()
"""SQL code:
2021-04-25 14:08:16,251 INFO sqlalchemy.engine.Engine DELETE FROM team WHERE team.id = ?
2021-04-25 14:08:16,252 INFO sqlalchemy.engine.Engine [generated in 0.00073s] (1,)
"""
本文收集自互联网，转载请注明来源。
如有侵权，请联系 [email protected] 删除。
我来说两句