On Feb 13, 2011, at 1:39 PM, Andrey Gladilin wrote:
> I am trying to create a version column which would use values from a
> single postgresql sequence.
>
> record_versions_id_seq = Sequence('record_versions_id_seq')
>
> class TimestampMixin(object):
> created_at = Column(DateTime, default=func.now())
> record_version = Column(Integer, nullable=False,
> default=func.nextval("record_versions_id_seq"))
>
> __mapper_args__ = {
> 'version_id_col': record_version,
> 'version_id_generator': lambda v:
> func.nextval("record_versions_id_seq")
> }
>
> class Team(Base, NameMixin, TimestampMixin):
> __tablename__ = 'teams'
> id = Column(Integer, primary_key=True)
>
> There are other tables like Team inheriting TimestampMixin. And here I
> have two problems:
>
> 1. Decribed code does not work for update. I.e when I update the
> record from Team, the record_version column value is not getting
> changed. So to workaround this problem I have to explicitly specify
> __mapper_args__ in Team class.
if Base or NameMixin is also modifying __mapper_args__, those will override
what TimestampMixin returns. The __mapper_args__ from different mixins need
to be combined manually for the final product. Some background at
http://www.sqlalchemy.org/docs/orm/extensions/declarative.html#combining-table-mapper-arguments-from-multiple-mixins
> 2. Code lambda v: func.nextval("record_versions_id_seq") does not
> work. I guess this code is incorrect, so could you help me to create a
> correct one please?
you'd need to execute the function through a connection, and you can use the
Sequence object directly:
lambda v: some_engine.execute(record_versions_id_seq)
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