这是我的代码:
from sqlalchemy import create_engine, Column, Integer
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker
database_url = 'mysql://some_path'
engine = create_engine(database_url)
Base = declarative_base(engine)
class Users(Base):
__tablename__ = 'Users'
__table_args__ = {'autoload':True}
metadata = Base.metadata
Session = sessionmaker(bind=engine)
session = Session()
它有效,但是...
是否可以在需要时绑定(bind)引擎,而不仅仅是在导入时?所以我可以将此实现包装到类中。
现在,我明白了
class Users(Base):
File "/usr/lib/python2.5/site-packages/SQLAlchemy-0.6.5-py2.5.egg/sqlalchemy/ext/declarative.py", line 1231, in __init__
_as_declarative(cls, classname, cls.__dict__)
File "/usr/lib/python2.5/site-packages/SQLAlchemy-0.6.5-py2.5.egg/sqlalchemy/ext/declarative.py", line 1122, in _as_declarative
**table_kw)
File "/usr/lib/python2.5/site-packages/SQLAlchemy-0.6.5-py2.5.egg/sqlalchemy/schema.py", line 209, in __new__
table._init(name, metadata, *args, **kw)
File "/usr/lib/python2.5/site-packages/SQLAlchemy-0.6.5-py2.5.egg/sqlalchemy/schema.py", line 260, in _init
msg="No engine is bound to this Table's MetaData. "
File "/usr/lib/python2.5/site-packages/SQLAlchemy-0.6.5-py2.5.egg/sqlalchemy/schema.py", line 2598, in _bind_or_error
raise exc.UnboundExecutionError(msg)
sqlalchemy.exc.UnboundExecutionError: No engine is bound to this Table's MetaData. Pass an engine to the Table via autoload_with=<someengine>, or associate the MetaData with an engine via metadata.bind=<someengine>
未指定引擎时:Base = declarative_base()
最佳答案
至少在 SQLAlchemy 0.9 中,您可以使用 DeferredReflection 延迟绑定(bind)。请参阅 Using Reflection with Declarative section of the manual 中的示例.
在那里,您可以找到以下示例(已简化):
from sqlalchemy.ext.declarative import declarative_base, DeferredReflection
Base = declarative_base(cls=DeferredReflection)
class Foo(Base):
__tablename__ = 'foo'
bars = relationship("Bar")
class Bar(Base):
__tablename__ = 'bar'
Base.prepare(e)
e 是引擎。
关于python - 在 SQLAlchemy 中使用 declarative_base 时,如何在需要时绑定(bind)引擎?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/4215920/