你很有可能don't需要发出两次提交;使用 sqlalchemy 会话的主要原因之一是它了解对象如何相互关联,并将以正确插入数据并正确表示所需结构的方式对其插入进行排序。这主要通过relationship
构造。这是一个简单的例子:
>>> from sqlalchemy import *
>>> from sqlalchemy.orm import *
>>> from sqlalchemy.ext.declarative import declarative_base
>>> Base = declarative_base()
>>> class A(Base):
... __tablename__ = "a_table"
... id = Column(Integer, primary_key=True)
...
>>> class B(Base):
... __tablename__ = "b_table"
... id = Column(Integer, primary_key=True)
... a_id = Column(Integer, ForeignKey(A.id))
... a = relationship(A)
...
>>> my_a = A()
>>> my_b = B()
>>> my_b.a = my_a
>>>
最重要的部分是我们声明之间的关系A
and B
通过B.a
。为了充分利用这一点,重要的是通过此关系属性来表达每个实例之间的关系,并让 sqlalchemy 负责设置a_id
列本身。
>>> engine = create_engine("sqlite:///:memory:")
>>> Base.metadata.create_all(engine)
>>> engine.echo = True
>>> Session = sessionmaker(engine)
>>>
>>> session = Session()
>>> session.add(my_a)
>>> session.add(my_b)
>>>
>>> session.commit()
With echo=True
,输出看起来有点像这样:
2011-09-16 17:19:22,367 INFO sqlalchemy.engine.base.Engine.0x...ed50 BEGIN (implicit)
2011-09-16 17:19:22,368 INFO sqlalchemy.engine.base.Engine.0x...ed50 INSERT INTO a_table DEFAULT VALUES
2011-09-16 17:19:22,368 INFO sqlalchemy.engine.base.Engine.0x...ed50 ()
2011-09-16 17:19:22,369 INFO sqlalchemy.engine.base.Engine.0x...ed50 INSERT INTO b_table (a_id) VALUES (?)
2011-09-16 17:19:22,369 INFO sqlalchemy.engine.base.Engine.0x...ed50 (1,)
2011-09-16 17:19:22,369 INFO sqlalchemy.engine.base.Engine.0x...ed50 COMMIT
请注意,my_a
对象被插入,sqlalchemy 读取分配的主键并将其用于插入my_b
.