Mysql 在SQLAlchemy中设计数据库模式时,我需要多久使用一次;背景参考“;?
我来自Django世界,从来没有“背景”。我所做的就是定义外键 就这样Mysql 在SQLAlchemy中设计数据库模式时,我需要多久使用一次;背景参考“;?,mysql,database,orm,schema,sqlalchemy,Mysql,Database,Orm,Schema,Sqlalchemy,我来自Django世界,从来没有“背景”。我所做的就是定义外键 就这样 为什么要使用backref?要了解backref,请检查给定的示例 from sqlalchemy import create_engine, ForeignKey from sqlalchemy.ext.declarative import declarative_base from sqlalchemy.orm import relationship, backref from sqlalchemy import Col
为什么要使用backref?要了解backref,请检查给定的示例
from sqlalchemy import create_engine, ForeignKey
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship, backref
from sqlalchemy import Column, Integer, String
from sqlalchemy import Table, Text
engine = create_engine('mysql://root:ababab@localhost/alctest',
echo=False)
Base = declarative_base()
class User(Base):
__tablename__ = 'users'
id = Column(Integer, primary_key = True)
name = Column(String(100))
fullname = Column(String(100))
password = Column(String(100))
def __init__(self, name, fullname, password):
self.name = name
self.fullname = fullname
self.password = password
def __repr__(self):
return "<User('%s','%s', '%s')>" % (self.name, self.fullname, self.password)
class Address(Base):
__tablename__ = 'addresses'
id = Column(Integer, primary_key = True)
email_address = Column(String(100), nullable=False)
#foreign key, must define relationship
user_id = Column(Integer, ForeignKey('users.id'))
user = relationship("User", backref = backref('addresses',order_by=id))
但是如果您将使用backref
,那么当您访问该属性时,sqlalchemy将运行此查询
现在在我们的示例中,如果您要访问userobject.addresses
,那么它将运行查询
SELECT * FROM addresses WHERE user_id = userobject.id
在用户
模型中没有类似地址
的属性。这将由backref
从地址
模型的用户
属性设置。
SELECT * FROM addresses WHERE user_id = userobject.id