在 SQLAlchemy 中定义表时，如何将函数(依赖于其他列的表达式)定义为列的默认值? [英] How to define a function(expression dependant on other columns) as a default value to a column while defining table in SQLAlchemy?

问题描述

如何向SQLAlchemy表中的某列添加一个函数/表达式，该函数/表达式将参数作为其他列作为默认值?例如:我想将 c 定义为 2*x(其他列)的列；它应该保存在数据库中(也可以在其他表中).在这种情况下可以使用@hybrid_property 装饰器吗?

How to add a function/expression which takes arguments as other columns as a default value to a column in the table of SQLAlchemy? For example: I want to define c as a column which is 2*x(other column);which should be saved in the database(could be in other table too). Can @hybrid_property decorator be used in this context?

from sqlalchemy import Column, Integer
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import Session, aliased
from sqlalchemy.ext.hybrid import hybrid_property, hybrid_method
from sqlalchemy import create_engine
from sqlalchemy import MetaData
from sqlalchemy.orm import sessionmaker


engine = create_engine('sqlite:///Helloworld.db', echo=False)
Session = sessionmaker(bind=engine)
metadata = MetaData(engine)
Base = declarative_base()

class HelloWorld(Base):
    __tablename__ = 'helloworld'
    pm_key = Column(Integer, primary_key=True)
    x = Column(Integer, nullable=False)
    c = Column(Integer,default=2*x)

Base.metadata.create_all(engine)

推荐答案

这是可能的.下面我只是添加了一段代码，你可以试试.更多我认为 this帮助你.

It is possible. Below I'am just adding a piece of code you can try . For more I think this will help you.

def mydefault(context):
    return context.current_parameters.get('X')

class HelloWorld(Base):
    __tablename__ = 'helloworld'
    pm_key = Column(Integer, primary_key=True)
    x = Column(Integer, nullable=False)
    c = Column(Integer,default=mydefault)

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