我有以下代码想要更新：
In [147]: dff = pd.crosstab(df.Item, df.User)
In [148]: dff = dff.dot(dff.T)
In [149]: np.fill_diagonal(dff.values, 0)
In [150]: dff
Out[150]:
Item 1 2 3
Item
1 0 1 1
2 1 0 0
3 1 0 0
在测试中，我使用def add_electricity_reading(
*, period_usage, period_started_at, is_estimated, customer_pk
):
from sqlalchemy.dialects.postgresql import insert
values = dict(
customer_pk=customer_pk,
period_usage=period_usage,
period_started_at=period_started_at,
is_estimated=is_estimated,
)
insert_stmt = insert(ElectricityMeterReading).values(**values)
do_update_stmt = insert_stmt.on_conflict_do_update(
constraint=ElectricityMeterReading.__table_args__[0].name,
set_=dict(
period_usage=period_usage,
period_started_at=period_started_at,
is_estimated=is_estimated,
)
)
conn = DBSession.connection()
conn.execute(do_update_stmt)
return DBSession.query(ElectricityMeterReading).filter_by(**dict(
period_usage=period_usage,
period_started_at=period_started_at,
customer_pk=customer_pk,
is_estimated=is_estimated,
)).one()
def test_updates_existing_record_for_started_at_if_already_exists():
started_at = datetime.now(timezone.utc)
existing = add_electricity_reading(
period_usage=0.102,
customer_pk=customer.pk,
period_started_at=started_at,
is_estimated=True,
)
started_at = existing.period_started_at
reading = add_electricity_reading(
period_usage=0.200,
customer_pk=customer.pk,
period_started_at=started_at,
is_estimated=True,
)
# existing record was updated
assert reading.period_usage == 0.200
assert reading.id == existing.id
添加现有记录，然后再次执行查询，但更改为period_usage=0.102。当底部的最终查询返回记录时，period_usage仍为0.102。
知道为什么会这样吗？
答案 0 :(得分：0)
此行为在"What does the Session do?"下的“会话基础”中进行了说明，该会话将引用保存到已加载的对象中，该对象称为identity map结构，因此确保每个主键值仅包含1个唯一对象在会话的生存期内一次存在。您可以在自己的代码中使用以下断言来验证这一点：
assert existing is reading
您正在执行的Core插入（或更新）语句不会使会话与数据库中发生的更改保持同步，例如Query.update()。为了获取新值，您可以expire唯一对象的ORM加载状态：
DBSession.expire(existing) # or reading, does not matter
# existing record was updated
assert reading.period_usage == 0.200
assert reading.id == existing.id