时间：2021-07-01 10:21:17 帮助过：2人阅读
from sqlalchemy import Table, Column, Integer, ForeignKey
from sqlalchemy.orm import relationship
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
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<br>class Parent(Base):
__tablename__ = ‘parent‘
id = Column(Integer, primary_key=True)
children = relationship("Child")
class Child(Base):
__tablename__ = ‘child‘
id = Column(Integer, primary_key=True)
parent_id = Column(Integer, ForeignKey(‘parent.id‘))
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To establish a bidirectional relationship in one-to-many, where the “reverse” side is a many to one, specify an additional relationship() and connect the two using therelationship.back_populates parameter:
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class Parent(Base):
__tablename__ = ‘parent‘
id = Column(Integer, primary_key=True)
children = relationship("Child", back_populates="parent")
class Child(Base):
__tablename__ = ‘child‘
id = Column(Integer, primary_key=True)
parent_id = Column(Integer, ForeignKey(‘parent.id‘))
parent = relationship("Parent", back_populates="children")
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Child will get a parent attribute with many-to-one semantics.
Alternatively, the backref option may be used on a single relationship() instead of usingback_populates:
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class Parent(Base):
__tablename__ = ‘parent‘
id = Column(Integer, primary_key=True)
children = relationship("Child", backref="parent")
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附，原生sql join查询
几个Join的区别 http://stackoverflow.com/questions/38549/difference-between-inner-and-outer-joins
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select host.id,hostname,ip_addr,port,host_group.name from host right join host_group on host.id = host_group.host_id
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in SQLAchemy
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session.query(Host).join(Host.host_groups).filter(HostGroup.name==‘t1‘).group_by("Host").all()
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group by 查询
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select name,count(host.id) as NumberOfHosts from host right join host_group on host.id= host_group.host_id group by name;
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in SQLAchemy
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from sqlalchemy import func
session.query(HostGroup, func.count(HostGroup.name )).group_by(HostGroup.name).all()
#another example
session.query(func.count(User.name), User.name).group_by(User.name).all() SELECT count(users.name) AS count_1, users.name AS users_name
FROM users GROUP BY users.name
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SqlAlchemy ORM
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