On Jul 21, 2011, at 2:11 AM, Fayaz Yusuf Khan wrote:
> Hi,
> I have this declarative table model:
> http://paste.pound-python.org/show/9857/
The short answer is you can't do it that way right now. The "user" and
"timestamp" columns of C can't get assigned to the Table by declarative because
they've already been instrumented by the mapping of the Timeline class - the
columns generated on the TMixin class are replaced by the instrumented versions
of Timeline.
You'd have to forego the usage of mixins here or have C() use a mixin that
isn't in the hierarchy of Timeline.
Ticket #2226 is added to see if this can be fixed.
> ==========================================================
> from sqlalchemy import Column, String, ForeignKeyConstraint, Integer
> from sqlalchemy.ext.declarative import declarative_base, declared_attr
>
>
> class TableName(object):
> @declared_attr
> def __tablename__(cls):
> return cls.__name__
>
>
> Base=declarative_base(cls=TableName)
>
>
> class TMixin(object):
>
> @declared_attr
> def user(cls):
> return Column(String, primary_key=True)
>
> @declared_attr
> def timestamp(cls):
> return Column(Integer, autoincrement=False, primary_key=True)
>
>
> class Timeline(TMixin, Base):
>
> snaptype = Column(Integer, primary_key=True, autoincrement=False)
>
> __mapper_args__ = {'polymorphic_on': snaptype}
>
>
> class CMixin(TMixin):
>
> @declared_attr
> def __table_args__(cls):
> return (ForeignKeyConstraint(
> ['user', 'timestamp'],
> ['Timeline.user', 'Timeline.timestamp']),)
>
> @declared_attr
> def __mapper_args__(cls):
> return {'polymorphic_identity': CMixin.__subclasses__().index(cls)}
>
>
> class C(CMixin, Timeline):
>
> pass
>
> ==========================================================
>
> But on running this code, I get:
> ==========================================================
> Traceback (most recent call last):
> File "schema.py", line 45, in <module>
> class C(CMixin, Timeline):
> File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/ext/declarative.py",
> line 1129, in __init__
> _as_declarative(cls, classname, cls.__dict__)
> File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/ext/declarative.py",
> line 1027, in _as_declarative
> **table_kw)
> File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/schema.py", line
> 265, in __new__
> table._init(name, metadata, *args, **kw)
> File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/schema.py", line
> 340, in _init
> self._init_items(*args)
> File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/schema.py", line 64,
> in _init_items
> item._set_parent_with_dispatch(self)
> File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/events.py", line
> 227, in _set_parent_with_dispatch
> self._set_parent(parent)
> File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/schema.py", line
> 2010, in _set_parent
> col = table.c[col]
> File "/usr/local/lib/python2.7/dist-
> packages/sqlalchemy/util/_collections.py", line 88, in __getitem__
> return self._data[key]
> KeyError: 'user'
> ==========================================================
>
> I don't get any error if C isn't inheriting from Timeline (ie, no joint-table
> inheritance). What could be wrong here?
>
> sqlalchemy.__version__ = '0.7.1'
>
> And thanks in advance.
>
> --
> Fayaz Yusuf Khan
> Cloud developer and designer
> Dexetra SS, Kochi, India
> fayaz.yusuf.khan_AT_gmail_DOT_com
> fayaz_AT_dexetra_DOT_com
> +91-9746-830-823
> <schema.py>
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