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SQLAlchemy actively applied column defaults
from datetime import datetime
from sqlalchemy import Column, DateTime, Integer, Text, func, inspect
from sqlalchemy.ext.declarative import as_declarative, declared_attr
from sqlalchemy.sql.functions import Function
def defaults_included_constructor(instance, **kwds):
mapper = inspect(instance).mapper
for column in mapper.columns:
if (default := column.default) is not None:
if not isinstance(default.arg, Function) and not callable(default.arg):
attr = mapper.get_property_by_column(column)
kwds.setdefault(attr.key, default.arg)
for attr, value in kwds.items():
setattr(instance, attr, value)
class Base:
def __tablename__(cls):
return cls.__name__.lower()
class User(Base):
id = Column(Integer, primary_key=True)
name = Column(Text)
email = Column(Text)
role = Column("role_name", Text, default="user")
created_at = Column(DateTime,
updated_at = Column(DateTime, default=datetime.utcnow)
def main():
john = User(name="John")
assert john.role == "user"
assert john.created_at is None
assert john.updated_at is None
print("John has a default role of 'user', pre-flush")
claire = User(name="Claire", role="admin")
assert claire.role == "admin"
print("Claire has a non-default role of 'admin', pre-flush")
if __name__ == "__main__":
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