python – 如何在分配给未映射到SQLAlchemy列的属性时引发异常？
发布时间：2020-12-20 13:29:38 所属栏目：Python 来源：网络整理
导读：使用SQLAlchemy,我发现有时候我错误地键入了一个映射到列的属性的名称,这导致很难捕获错误： class Thing(Base): foo = Column(String)thing = Thing()thing.bar = "Hello" # a typo,I actually meant thing.fooassert thing.bar == "Hello" # works here,as
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使用SQLAlchemy,我发现有时候我错误地键入了一个映射到列的属性的名称,这导致很难捕获错误：
class Thing(Base):
foo = Column(String)
thing = Thing()
thing.bar = "Hello" # a typo,I actually meant thing.foo
assert thing.bar == "Hello" # works here,as thing.bar is a transient attribute created by the assignment above
session.add(thing)
session.commit() # thing.bar is not saved in the database,obviously
...
# much later
thing = session.query(Thing)...one()
assert thing.foo == "Hello" # fails
assert thing.bar == "Hello" # fails,there's no even such attribute
有没有办法配置映射类,因此分配给未映射到SQLAlchemy列的任何内容都会引发异常？ 解决方法
好的,解决方案似乎是覆盖基类的__setattr__方法,这允许我们在设置之前检查属性是否已经存在.
class BaseBase(object):
"""
This class is a superclass of SA-generated Base class,which in turn is the superclass of all db-aware classes
so we can define common functions here
"""
def __setattr__(self,name,value):
"""
Raise an exception if attempting to assign to an atribute which does not exist in the model.
We're not checking if the attribute is an SQLAlchemy-mapped column because we also want it to work with properties etc.
See https://stackoverflow.com/questions/12032260/ for more details.
"""
if name != "_sa_instance_state" and not hasattr(self,name):
raise AttributeError("Attribute %s is not a mapped column of object %s" % (name,self))
super(BaseBase,self).__setattr__(name,value)
Base = declarative_base(cls=BaseBase)
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