Question

我有Postgres DB，其中包含待处理操作表。枚举操作中的一列，具有枚举状态。我使用标准的python（2.7）枚举，使用AutoNumber（myenum.py）：

class AutoNumber(enum.Enum):
    def __new__(cls):
        value = len(cls.__members__) + 1
        obj = object.__new__(cls)
        obj._value_ = value
        return obj

class MyStatus(AutoNumber):

    INITIAL = ()
    ACCEPTED = ()
    DENIED = ()
    ACK_PENDING = ()
    AUTHORIZED = ()
    ACTIVE = ()
    END = ()
    DELETED = ()
# end enum

该表看起来像（也在myenum.py中）：

Base = declarative_base()

class MyOperation(Base):

    __tablename__ = 'operations'

    id  = Column( Integer, primary_key=True )

    status = Column( Enum(MyStatus) )
    status_message = Column( String )
    status_time = Column( DateTime )

    def __repr__(self):
        return "<MyOperation(%s, %s, %s, %s)>" % \
            ( self.id, self.status, self.status_time, self.status_message )
# end class

一般来说这很好用。在定义MyStatus（myoper.py）的相同文件中，我可以更改状态并将其保存回数据库，并且工作正常：

def checkOper( oper ):
    oper.status = MyStatus.DENIED
    oper.status_message = "failed check (internal)"
    oper.status_time = datetime.datetime.utcnow()

以下是我如何称呼它（在myoper.py内）

    checkOper( oper )
    session.add(oper)
    session.commit()

这都在同一个文件中（myoper.py）。

但是，如果我将oper对象传递给外部函数，并且IT更改状态，那么我会得到sqlalchemy.exc.StatementError。

这是外部函数（myoper_test.py）：

import datetime
from myoper import MyStatus

def extCheckOper( oper ):
    oper.status = MyStatus.DENIED
    oper.status_message = "failed check (external)"
    oper.status_time = datetime.datetime.utcnow()

以下是我如何称呼它（来自myoper.py）：

    from myoper_test import extCheckOper
    extCheckOper( oper )
    session.add(oper)
    session.commit()

这是堆栈跟踪：

Traceback (most recent call last):
  File "./myoper.py", line 120, in <module>
    session.commit()
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/session.py", line 906, in commit
    self.transaction.commit()
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/session.py", line 461, in commit
    self._prepare_impl()
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/session.py", line 441, in _prepare_impl
    self.session.flush()
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/session.py", line 2177, in flush
    self._flush(objects)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/session.py", line 2297, in _flush
    transaction.rollback(_capture_exception=True)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/util/langhelpers.py", line 66, in __exit__
    compat.reraise(exc_type, exc_value, exc_tb)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/session.py", line 2261, in _flush
    flush_context.execute()
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/unitofwork.py", line 389, in execute
    rec.execute(self)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/unitofwork.py", line 548, in execute
    uow
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/persistence.py", line 177, in save_obj
    mapper, table, update)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/persistence.py", line 737, in _emit_update_statements
    execute(statement, multiparams)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line 945, in execute
    return meth(self, multiparams, params)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/sql/elements.py", line 263, in _execute_on_connection
    return connection._execute_clauseelement(self, multiparams, params)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line 1053, in _execute_clauseelement
    compiled_sql, distilled_params
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line 1121, in _execute_context
    None, None)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line 1402, in _handle_dbapi_exception
    exc_info
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/util/compat.py", line 203, in raise_from_cause
    reraise(type(exception), exception, tb=exc_tb, cause=cause)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line 1116, in _execute_context
    context = constructor(dialect, self, conn, *args)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/default.py", line 639, in _init_compiled
    for key in compiled_params
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/default.py", line 639, in <genexpr>
    for key in compiled_params
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/sql/sqltypes.py", line 1446, in process
    value = self._db_value_for_elem(value)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/sql/sqltypes.py", line 1354, in _db_value_for_elem
    '"%s" is not among the defined enum values' % elem)
sqlalchemy.exc.StatementError: (exceptions.LookupError) "MyStatus.DENIED" is not among the defined enum values [SQL: u'UPDATE operations SET status=%(status)s, status_message=%(status_message)s, status_time=%(status_time)s WHERE operations.id = %(operations_id)s'] [parameters: [{'status': <MyStatus.DENIED: 6>, 'status_time': datetime.datetime(2017, 10, 18, 20, 22, 44, 350035), 'status_message': 'failed check (external)', 'operations_id': 3}]]

我已尝试检查内部文件和外部文件中的类型，但其方式列为<enum 'MyStatus'>。

我发现，如果我将oper.status分配给枚举.name，那那就可以了：

def extCheckOper( oper ):
    oper.status = MyStatus.AUTHORIZED.name
    oper.status_message = "authorized check (external)"
    oper.status_time = datetime.datetime.utcnow()

但那显然很难看。

所以 - 我做错了什么？ MyStatus在其定义的文件中有什么不同，而不是一个搞乱SQL Alchemy的外部文件？

Answer 1

我将此问题发布到SQL Alchemy邮件列表并得到了答案。 Link to thread

结果发现这个关于python的“问题”之一并没有与SQL Alchemy有任何关系。以下是参考：Executing Main Module Twice。

在这种特殊情况下，当我执行脚本时，MyStatus是使用特定的id（类型上的python句柄）创建的。但是当myoper_test从myoper导入MyStatus时，它是用不同的id创建的。

因此，当extCheckOper将一个MyStatus值分配给status字段时，它是一个不同的 MyStatus而不是SQL Alchemy创建的数据库映射，所以当SQL Alchemy尝试将其保存到DB时， “是”运算符失败，因为（外部）MyStatus与（原始）MyStatus不同。

有几种不同的解决方法。一种方法是不将代码作为main运行（在将 main 代码移出main（）函数后）：

$ python -c "from myoper import main; import sys; main(*sys.argv[1:])" ext_check 1

更好的解决方案是完全避免此问题 - 将外部调用的代码移动到内部测试脚本。 main 中的代码主要位于主脚本内（对不起，无法抗拒...... :-)）。

外部文件

1 个答案: