After failing to use vars to change db.Model(flask-sqlalchemy) value I solved it by using
setattr
instead, but after reading doc still don't get the difference betweenvars
andsetattr
.
这是我尝试过的
变量
失败
代码
from flask_sqlalchemy import SQLAlchemy
db = SQLAlchemy()
def set_option_parameters(var, option_keys, options):
for option_key in options:
if option_key in option_keys and options[option_key] is not None:
vars(var)[option_key] = options[option_key]
# setattr(var, option_key, options[option_key])
class Application(db.Model):
id = db.Column(db.BigInteger(), primary_key=True, autoincrement=True)
name = db.Column(db.VARCHAR(20), nullable=False)
...
def __init__(self, options):
option_keys = set(["name"])
set_option_parameters(self, option_keys, options)
def modification(self, options):
modifiable = set(["name"])
set_option_parameters(self, modifiable, options)
vars(var)[option_key] = options[option_key]
在初始化 Application
对象时工作正常,但在 中失败修改
(名称
未更改)。
日志/测试
我尝试在db.session.commit()
之前打印application.__dict__
,它确实被修改了!
application = Application.query.filter_by(id=args["id"]).first()
# args["name"] is not None
app.logger.info(f"Before: {application.__dict__}")
application.modification(args)
app.logger.info(f"After: {application.__dict__}")
db.session.commit()
输出
[2019-02-27 11:22:59,209] INFO in equipmentbaseapplicationhandler: Before:{'_sa_instance_state': <sqlalchemy.orm.state.InstanceState object at 0x7f718ac2b588>, 'id': 9, 'name': 'old_name'}
[2019-02-27 11:22:59,209] INFO in equipmentbaseapplicationhandler: After:{'_sa_instance_state': <sqlalchemy.orm.state.InstanceState object at 0x7f718ac2b588>, 'id': 9, 'name': 'new_name'}
但是当我 checkin mysql时,它不起作用
setattr
成功
然后我在函数 set_option_parameters
中更改为 setattr(var, option_key, options[option_key])
。
它在初始化和修改中都运行良好,并且 application.__dict__
的输出是相同的!
最佳答案
From the docs对于变量
:
Objects such as modules and instances have an updateable dict attribute; however, other objects may have write restrictions on their dict attributes (for example, classes use a types.MappingProxyType to prevent direct dictionary updates).
查看 SQLAlchemy 源代码(例如 here ),访问时返回 some_model.__dict__
的副本是一种常见模式,而不是返回 __dict__
本身。因此,您可能会更新副本而不是原始版本。否则,即使字典发生变化,字典也可能被属性本身覆盖。
setattrs
是正确的模式,并且更明确。
关于python - `vars` 和 `setattr` 和有什么区别?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/54897575/