SQLAlchemy使用笔记--SQLAlchemy ORM(二)
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参考:
http://docs.sqlalchemy.org/en/rel_1_0/orm/tutorial.html#building-a-relationship
http://docs.sqlalchemy.org/en/rel_1_0/orm/tutorial.html#working-with-related-objects
建立表之间带关系
建立外建
在address添加user的外键
from sqlalchemy import ForeignKey, Column, String, Integerfrom sqlalchemy.orm import relationshipclass User(Base): __tablename__ = 'users' id = Column(Integer, primary_key=True) name = Column(String) fullname = Column(String) password = Column(String)class Address(Base): __tablename__ = 'addresses' id = Column(Integer, primary_key=True) email_address = Column(String, nullable=False) user_id = Column(Integer, ForeignKey('users.id')) user = relationship('User', backref=backref('addresses', order_by=id))
relationship中的backref参数使用形式:
backref="addresses" #直接使用表名的字符串backref=backref('addresses') #使用backref函数backref=backref('addresses', order_by=id)) #brackref函数可以添加参数,详见http://docs.sqlalchemy.org/en/rel_1_0/orm/backref.html#backref-arguments
可以使用user.addresses 从user获取address 和,使用address.users 虫address获取user
backref 会在User跟Address上都加上关系,它本质是:
from sqlalchemy import Integer, ForeignKey, String, Columnfrom sqlalchemy.ext.declarative import declarative_basefrom sqlalchemy.orm import relationshipBase = declarative_base()class User(Base): __tablename__ = 'user' id = Column(Integer, primary_key=True) name = Column(String) addresses = relationship("Address", back_populates="user")class Address(Base): __tablename__ = 'address' id = Column(Integer, primary_key=True) email = Column(String) user_id = Column(Integer, ForeignKey('user.id')) user = relationship("User", back_populates="addresses")
relationship中的
添加
>>> jack.addresses = [... Address(email_address='jack@google.com'),... Address(email_address='j25@yahoo.com')]
获取
>>> jack.addresses[1]<Address(email_address='j25@yahoo.com')>>>> jack.addresses[1].user<User(name='jack', fullname='Jack Bean', password='gjffdd')>
commit
session.add(jack)session.commit()
address 会自动的添加
one to many 关系
class Parent(Base): __tablename__ = 'parent' id = Column(Integer, primary_key=True) children = relationship("Child", backref="parent")class Child(Base): __tablename__ = 'child' id = Column(Integer, primary_key=True) parent_id = Column(Integer, ForeignKey('parent.id'))
many to one 关系
class Parent(Base): __tablename__ = 'parent' id = Column(Integer, primary_key=True) child_id = Column(Integer, ForeignKey('child.id')) child = relationship("Child", backref="parents")class Child(Base): __tablename__ = 'child' id = Column(Integer, primary_key=True)
one to one 关系
from sqlalchemy.orm import backrefclass Parent(Base): __tablename__ = 'parent' id = Column(Integer, primary_key=True) child_id = Column(Integer, ForeignKey('child.id')) child = relationship("Child", backref=backref("parent", uselist=False))class Child(Base): __tablename__ = 'child' id = Column(Integer, primary_key=True)
many to many 关系
需要一个中间表和在relatonship 添加secondary参数
association_table = Table('association', Base.metadata, Column('left_id', Integer, ForeignKey('left.id')), Column('right_id', Integer, ForeignKey('right.id')))class Parent(Base): __tablename__ = 'left' id = Column(Integer, primary_key=True) children = relationship("Child", secondary=association_table, backref="parents")class Child(Base): __tablename__ = 'right' id = Column(Integer, primary_key=True)
这样在child添加删除parent或者parent添加删除child时,无需对中间表进行操作,直接添加删除即可。
parent.children.append(child)child.parents.append(parent)
也可以 使用类来创建中间表,这样可以在中间表中保存一些其他的信息。但是就不能想前面一样自动对中间表进行操作。
class Association(Base): __tablename__ = 'association' left_id = Column(Integer, ForeignKey('left.id'), primary_key=True) right_id = Column(Integer, ForeignKey('right.id'), primary_key=True) extra_data = Column(String(50)) child = relationship("Child", back_populates="parents") parent = relationship("Parent", back_populates="children")class Parent(Base): __tablename__ = 'left' id = Column(Integer, primary_key=True) children = relationship("Association", back_populates="parent")class Child(Base): __tablename__ = 'right' id = Column(Integer, primary_key=True) parents = relationship("Association", back_populates="child")
join 操作
可以使用Query.join()
>>> session.query(User).join(Address).\... filter(Address.email_address=='jack@google.com').\... all()[<User(name='jack', fullname='Jack Bean', password='gjffdd')>]
在User上可以直接使用join(Address) 因为只有一个外建在User和Address之间,其他join形式:
query.join(Address, User.id==Address.user_id) # explicit conditionquery.join(User.addresses) # specify relationship from left to rightquery.join(Address, User.addresses) # same, with explicit targetquery.join('addresses') # same, using a string
使用外链接
query.outerjoin(User.addresses) # 默认是左外连接。
当query中有多个实体点使用,使用join默认join追左边的那个,
例如:
query = session.query(User, Address).join(User) # 报错query = session.query(Address, User).join(User) # 正确
如果想自定使用join那个表,可以使用select_form
query = Session.query(User, Address).select_from(Address).join(User)
alias 别名
如果想join自己,可以使用别名
from sqlalchemy.orm import aliasedadalias1 = aliased(Address)adalias2 = aliased(Address)for username, email1, email2 in \ session.query(User.name, adalias1.email_address, adalias2.email_address).\ join(adalias1, User.addresses).\ join(adalias2, User.addresses).\ filter(adalias1.email_address=='jack@google.com').\ filter(adalias2.email_address=='j25@yahoo.com'): print(username, email1, email2)
使用子查询
直接看官方文档的例子:
>>> from sqlalchemy.sql import func>>> stmt = session.query(Address.user_id, func.count('*').\... label('address_count')).\... group_by(Address.user_id).subquery()>>> for u, count in session.query(User, stmt.c.address_count).\... outerjoin(stmt, User.id==stmt.c.user_id).order_by(User.id):... print(u, count)<User(name='ed', fullname='Ed Jones', password='f8s7ccs')> None<User(name='wendy', fullname='Wendy Williams', password='foobar')> None<User(name='mary', fullname='Mary Contrary', password='xxg527')> None<User(name='fred', fullname='Fred Flinstone', password='blah')> None<User(name='jack', fullname='Jack Bean', password='gjffdd')> 2
使用EXISTS
看官方文档的例子:
>>> from sqlalchemy.sql import exists>>> stmt = exists().where(Address.user_id==User.id)SQL>>> for name, in session.query(User.name).filter(stmt):... print(name)jack
等价于:
>>> for name, in session.query(User.name).\... filter(User.addresses.any()):... print(name)jack
user.addresses 可以像user中其他属性一样在filter使用==、!=、any等等。
query.filter(Address.user == someuser)query.filter(Address.user != someuser)query.filter(Address.user == None)query.filter(User.addresses.contains(someaddress))query.filter(User.addresses.any(Address.email_address == 'bar'))# also takes keyword arguments:query.filter(User.addresses.any(email_address='bar'))query.filter(Address.user.has(name='ed'))session.query(Address).with_parent(someuser, 'addresses')
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