使用sqlalchemy中的计算列更新表 [英] update tables with computed columns in sqlalchemy
问题描述
我正在使用SQLalchemy在旧版MSSQL数据库中进行工作,对此我具有声明性映射.
该数据库有几个具有计算列的表.我可以很好地阅读它们,但是(当然)写入计算列是行不通的.但是,当我创建并尝试保存ORM对象时,SQLAlchemy仍尝试在这些列中保存无"值,从而导致错误.
I'm working in a legacy MSSQL database using SQLalchemy, for which I have a declarative mapping.
This database has several tables that have computed columns. I can read them fine, but (of course) writing to a computed column doesn't work. However, when I create and try to save an ORM object, SQLAlchemy still tries to save 'None' values in these columns, resulting in an error.
我在网上找到了一些示例,这些示例应该使用SQLAlchemy的hybrid_property装饰器将特定列设置为只读",但是即使实现了该错误,仍然会出现相同的错误(The column "tlog_real_timehh" cannot be modified because it is either a computed column or is the result of a UNION operator.
).
I have found some examples online that should make specific columns "read-only" by using SQLAlchemy's hybrid_property decorator, but even after implementing that, the same error (The column "tlog_real_timehh" cannot be modified because it is either a computed column or is the result of a UNION operator.
) still comes up.
代码如下-映射:
class transactionlog(Base):
__tablename__ = 'transactionlog'
tlog_id = Column(VARCHAR(length=36), primary_key=True, nullable=False)
tlog_ppl_id = Column(VARCHAR(length=36), ForeignKey('people.ppl_id'))
tlog_evtt_id = Column(VARCHAR(length=5))
tlog_testrun = Column(BIT())
tlog_Data = Column(NVARCHAR(length=300))
tlog_price = Column(DECIMAL(precision=18, scale=2))
tlog_comment = Column(NVARCHAR(length=1000))
_tlog_real_timehh = Column('tlog_real_timehh', INTEGER())
_tlog_real_timemm = Column('tlog_real_timemm', INTEGER())
_tlog_real_timess = Column('tlog_real_timess', INTEGER())
_tlog_fin_booking = Column('tlog_fin_booking', BIT())
@hybrid_property
def tlog_real_timehh(self):
return self._tlog_real_timehh
@tlog_real_timehh.setter
def tlog_real_timehh(self, tlog_real_timehh):
self._tlog_real_timehh = tlog_real_timehh
@hybrid_property
def tlog_real_timemm(self):
return self._tlog_real_timemm
@tlog_real_timemm.setter
def tlog_real_timemm(self, tlog_real_timemm):
self._tlog_real_timemm = tlog_real_timemm
@hybrid_property
def tlog_real_timess(self):
return self._tlog_real_timess
@tlog_real_timess.setter
def tlog_real_timess(self, tlog_real_timess):
self._tlog_real_timess = tlog_real_timess
@hybrid_property
def tlog_fin_booking(self):
return self._tlog_fin_booking
@tlog_fin_booking.setter
def tlog_fin_booking(self, tlog_fin_booking):
self._tlog_fin_booking = tlog_fin_booking
以及应该添加新记录的代码:
and the code that should add a new record:
rem = Transactionlog()
rem.tlog_testrun = 0
rem.tlog_evtt_id = 'rem'
rem.tlog_Data = None
rem.tlog_comment = 'reminder'
rem.tlog_price = 0
db.session.add(rem)
db.session.flush()
我希望hybrid_property代码将计算的字段设为只读,但是似乎SQLAlchemy仍会尝试根据映射代码将其填充到INSERT语句中. (我在查看SQL语句时可以看到这一点.我无法发布该SQL语句,因为我在某种程度上将对象缩写为在StackOverflow上没有任何敏感数据.)
I would expect the hybrid_property code to make the computed fields read-only, but it seems that SQLAlchemy still tries to fill them in the INSERT statement, based on the mapping code. (I can see this when I look at the SQL statement. I cannot post the SQL statement, because I abbreviated the object somewhat to not have any sensitive data on StackOverflow).
问题是,为什么SQLAlchemy仍然尝试为tlog_real_timehh,tlog_real_timemm,tlog_real_timess和tlog_fin_booking插入值,并且如何防止这种情况发生?
The question is, why does SQLAlchemy still try to insert values for tlog_real_timehh, tlog_real_timemm, tlog_real_timess and tlog_fin_booking, and how can I prevent this?
感谢您可以给我任何指导.
埃里克
Thanks for any pointers you can give me.
Erik
推荐答案
标签 FetchedValue
:
Label server-generated columns with a FetchedValue
:
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
class A(Base):
__tablename__ = 'a'
id = Column(Integer, autoincrement=False, primary_key=True)
firstname = Column(String(50))
lastname = Column(String(50))
fullname = Column(String(100), FetchedValue())
e = create_engine("mssql+pyodbc://scott:tiger@ms_2005", echo=True)
Base.metadata.drop_all(e)
e.execute("""
CREATE TABLE a (
id INTEGER PRIMARY KEY,
firstname VARCHAR(50),
lastname VARCHAR(50)
)
""")
e.execute("ALTER TABLE a ADD fullname AS firstname + ' ' + lastname")
sess = Session(e)
sess.add_all([
A(id=1, firstname='ed', lastname='jones'),
A(id=2, firstname='wendy', lastname='smith'),
A(id=3, firstname='jack', lastname='bean')
])
sess.commit()
assert [
fname for fname, in
sess.query(A.fullname).order_by(A.id)
] == ['ed jones', 'wendy smith', 'jack bean']
e.execute("DROP TABLE a")
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